DRAFT
DRAFT FINAL
LINER/LOCATIONAL
ANALYSIS PROJECT
Prepared for:
U.S. Environmental Protection Agency
Solid Waste Branch
401 M Street, S.W.
Washington, D. C.
Prepared by:
Ert«.c Atlantic, Inc.
15 Campus Drive, Suite 100
Somerset, New Jersey 08873
July 1983
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DISCLAIMER
This report has not been reviewed by the U.S. Environmental
Protection Agency and is not approved as an official Agency
publication. The contents do not necessarily reflect the views
and policies of the EPA, nor does mention cif trade names or
canmercial products constitute endorsement or recanmendations
for use.
This report should be cited only as a DRAFT. The report
is one in a series of draft reports developed as part of the
Office of Solid Waste’s Liner/Location Analysis Project.
Because the reports are in draft form, there may be sane
inconsistencies between volumes in the series. EPA is currently
reviewing all the draft reports.
Land Disposal Branch
EPA Office of Solid Waste.
July 1983
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ACKNOWLEDGEMENTS
A number of individuals, agencies and firms were
instrumental in the timely completion of this comprehensive OSW
project. Mr. Robert Tonetti of EPA/OSW as the EPA Program ilana-
ger for the entire project, provided support and guidance in each
area. Mr. James Bachmaier, EPA/OSW, served as the Project Off i-
cer and provided technical coordination and liaison among the
several parts of the project.
The following organizations and individuals contributed
to the successful completion of the project:
EPA Office of Solid Waste, Mr. Glen Galen
Land Disposal Branch Mr. Alessi Otte
EPA Office of Research and Mr. Douglas Amman
Development Mr. Robert Landreth
Mr. Mike Roulier
Anderson-Nichols & Co., Inc. Mr. Anthony Donigian
Mr. Stuart Brown
Arthur D. Little, Inc. Mr. Warren 7. Lyman
Battelle, Pacific Northwest Mr. Steven B. abusaki
Laboratories
E. C. Jordan Company Mr. Dirk Brunner
GCA Corporation
Geraghty & Miller, Inc. Mr. Don Lundy
Illinois State Geological Mr. Robert Griffin
Survey
North Carolina State Dr. Wayne Skaggs
University
Research Triangle Institute Mr. Ralph Ely
Texas A & N University Dr. Kirk Brown
TRW, Energy and Dr. Masood Ghassezni
Environmental Division
U.S. Army Engineer Waterways Mr. Paul Schroeder
Experiment Station
A number of other individuals who contributed in various
ways to this project include the several manufacturing represen-
tatives, contractors and members of the scientific community who
were interviewed and consulted regarding the use and testing of
clay and synthetic liner materials.
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Ertec, Inc., (The Earth Technology Corporation) served
in a review and coordinating capacity in the project, and pre-
pared the three technical interim reports dealing with clay
caps/liners, synthetic caps/liners and the facility/locational
analysis. Mr. Joseph M. Sorge served as Project Manager for
Ertec. Review and report preparation responsibilities were car-
ried out by Mr. Sorge, Dr. Andrew Mills, Dr. James Tracy,
Mr. Joseph Kulikowski, Dr. .Dunstan Chen, Mr. Allen Blodgett,
Mr. Dean Gregg, and Dr. John Catts.
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TABLE OF CONTENTS
PAGE
1.0 EXECUTIVE SUMMARY 1-1
1.1 BACKGROUND 1-1
1.1.1 Part 264 - Interim Final Land Disposal. 1-2
Regulations
1.1.2 Program Objectives 1-3
1.1.3 EPA Response 1-5
1.2 LINER PERFORMANCE CONCLUSIONS 1-6
1.2.1 Clay Cap and Liner Summary 1-6
1.2.2 Synthetic Cap and Liner Summary 1-6
1.2.3 Cap and Liner Conclusions 1-7
1.3 FACILITY/LOCATIONAL ANALYSIS 1-8
1.4 RECOMMENDATIONS 1-10
1.4.1 Regulatory 1-11
1.4.2 Guidance Materials 1-14
1.4.3 Research Recommendations 1-15
2.0 INTRODUCTION 2-1
2.1 BACKGROUND 2-1
2.1.1 Part 264 - Interim Final Land Disposal 2-2
Regulations
2.1.2 Significant Issues Identified by the 2-3
Comments Received
2.1.3 EPA Response 2-6
2.2 OBJECTIVES OF THE PROGRAM 2-7
2.2.1 FMLs and Clay Liners 2-7
2.2.2 Locational Factors 2-8
2.2.3 Specific Goals 2—9
2.3 STUDY APPROACH 2-10
2.3.1 Liner Evaluation Approach 2-10
2.3.2 Facility/Locational Analysis 2-11
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TABLE OF CONTENTS (continued)
Page
3.0 COMPARISON OF CLAY AND SYNTHETIC CAP AND LINER 3-1
SYSTEMS
3.1 INTRODUCTION 3-1
3.2 ADVANTAGES AND DISADVANTAGES OF CLAY AND 3-2
SYNTHETIC LINERS
3.2.1 Advantages and Disadvantages of Clay 3-3
Liner Systems
3.2.2 Advantages and Disadvantages of 3-4
Synthetic Liner Systems
3.3 EFFECTIVE LINER LEAKAGE 3-6
3.3.1 Clay Liner Leakage 3-7
3.3.2 FML Leakage 3-9
3.3.3 Clay and FML Leakage 3-11
3.4 CHEMICAL RESISTANCE OF LINER MATERIALS 3-12
3.4.1 Chemical Resistance of Clay Liners 3-12
3.4.2 Chemical Resistance of FMLs 3-13
3.4.3 Clay and FML Chemical Resistance 3-15
3.5 INSTALLATION PROBLEMS 3-17
3.5.1 Clay Liner Installation 3-17
3.5.2 Synthetic Liner Installation 3-19
3.5.3 Clay and FML Installation 3-20
3.6 FAILURE MODES 3-21
3.6.1 Clay System Failure Modes 3-21
3.6.2 FML Failure Modes 3-23
3.6.3 Clay Liner and FML Failure 3-25
3.7 LONG TERM PERFORMANCE 3-26
3.7.1 Clay System Performance 3-26
3.7.2 Synthetic Liner Performance 3-27
3.7.3 Performance Improvement Projections 3-29
3.8 FML AND CLAY LINER CONCLUSIONS 3-33
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TABLE OF CONTENTS (continued)
Page
4.0 SIGNIFICANCE OF FACILITY AND LOCATIONAL FACTORS IN 4-1
MINIMIZING OR PREVENTING GROUND-WATER CONTAMINATION
4.1 FACTORS AFFECTING MIGRATION RATES 4-2
4.1.1 Facility Factors 4-2
4.1.2 Unsaturated-Zone Factors 4-4
4.1.3 Saturated-Zone Factors 4-6
4.1,4 Factors Not Examined 4-8
4.2 CONTAMINANT MIGRATION 1N THE SELECTED 4-10
LOCATIONAL SETTINGS
4.3 RELATIONSHIP BETWEEN FACILITY SETTINGS 4-12
AND LOCATIONAL SETTINGS
5.0 CONCLUSIONS 5-1
5.1 CONCLUSIONS REGARDING CLAY AND SYNTHETIC 5—i
LINER SYSTEMS
5.2 FACILITY AND LOCATIONAL FACTORS AFFECTING 5-3
LEACHATE MIGRATION
6.0 SIGNIFICANT ISSUES REGARDING LAND DISPOSAL 6-1
OF HAZARDOUS WASTE
6.1 QUALITY ASSURANCE - HOW MUCH IS ENOUGH 6-1
6.2 CONSERVATIVE FACILITY DESIGN 6-2
6.3 FACILITY DESIGNS AND LOCATIONAL FACTORS 6-3
FOR PARTICULARLY HAZARDOUS MATERIALS
6.4 EPA RESOURCE AND MANPOWER COMMITMENT 6-5
6.5 SITE SPECIFIC DESIGN CONSIDERATIONS 6-5
7.0 RECOMMENDATIONS 7-1
7.1 REGULATORY 7-1
7.2 GUIDAI CE MATERIALS 7-4
7.3 RESEARCH RECOMMENDATIONS 7-5
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1 .0 EXECUTIVE SUMMARY
The Environmental Protection Agency, Office of Solid
Waste, initiated an integrated study of current land disposal
technology in response to comments received following publication
of the Interim Final Land Disposal Regulations. - The project
incorporated investigation of the following major task areas:
o Clay Cap and Liner Systems
o Synthetic Cap and Liner Systems
o Facility/Locational Analysis
This report provides a summary of the principal
findings, conclusions, and recommendations developed during the
course of the EPA investigation. The conclusions and recom-
mendations presented are based largely on the professional evalu-
ation by experts of the limited information available on liner
performance and hydrogeologic modeling of hazardous waste manage-
ment facilities.
1 • 1 BACKGROUND
The EPA published the Interim Final Land Disposal regu-
lations on July 26, 1982, and provided a 120-day comment period
for interested parties. The comments received identified three
major issues regarding land disposal of hazardous waste: ques-
tions concerning the potential use of clay liners for disposal
facilities; questions concerning the long term reliability of
flexible membrane liners (FMLs); and, questions regarding the
importance of locational factors in facility design. The f ol-
lowing section provides a brief description of the regulatory
program, the principal comments received, and the project de-
veloped by the EPA to respond to the comments received.
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‘i.l,l Part 264 - Interim Final Land Disposal Regulations
The interim final regulations contain the following
major requirements for surface impoundments, waste piles, and
landfills. The regulations do not currently contain hydrogeo-
logic siting requirements. The requirements differ for disposal
facilities froni those for storage facilities. Surface impound-
inents can be either disposal or storage facilities, landfills are
disposal only, and waste piles are storage only.
o Each disposal facility, either surface impoundment
or landfill, must have a liner that is designed to
prevent waste from passing into the liner; storage
facilities must have a liner designed to prevent
waste migration out of the facility and into the
subsurface soil, ground water or surface water
during the active life of the facility.
o Waste piles and landf ills must have leachate collec-
tion and removal systems (LCRS), as well as r easures
to prevent run-on of liquids into the unit. The
LCRS must be operated during the active life of the
facility, and, for landfills, throughout the post-
closure care period as well.
o Storage impoundments must have all wastes and waste
residues either removed 1 decontaminated, or solidi-
fied at closure. Piles must have all wastes and
waste residues removed or decontaminated at closure.
o Disposal facilities must be closed by covering with
a cap that provides long-term minimization of liquid
migration through the closed facility. The cap must
be at least as impermeable as the bottom liner.
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1.1.2 Program Objectives
The comments received by the EPA following publication
of the regulations served to focus attention on two areas of
concern regarding hazardous waste management facilities. The
first area of concern involved the evaluation of perceived advan-
tages and disadvantages of the use of clay or synthetic liners at
land disposal facilities. The second area identified involved
the assessment of the importance of locational factors to dispo-
sal facility performance and safety. The specific comments re-
ceived regarding these major issues are discussed briefly in the
following sections.
Performance of Cap and Liner Systems
Comments were received contending that clay liners
could be effectively used for containment at disposal facilities.
In short, these commenters stated that clay liners are at least
as effective as synthetic liners for containing hazardous waste.
Further comments were received regarding the expected performance
life of FMLs and the current ability to install acceptable FML
seams in the field. Other commentsreceived relating to liner
performance include the following:
o The use of refined clays as a substitute for synthe-
tic liners.
o The use of soil cement and admix materials in com-
bination with FMLs.
o The extent to which natural soils and clays act to
attenuate leachate.
o The need for liner inspection and quality assurance
programs.
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o Ground-water monitoring exemptions.
o The effects of various facility design specifics.
Locational Factors
Numerous comments were received regarding the impor-
tance of locational factors to hazardous waste management faci-
lity design requirements. A brief summary of the major points
addressed follows:
o Should hazardous waste management facilities be
restricted from aquifer recharge areas and other
locations? What is the risk associated with loca-
ting facilities in various sensitive locations?
o Should the EPA require a minimum depth (perhaps
30 feet) to ground water below a facility?
o Should there be a minimum distance to surface-water
bodies?
o Is there a need for a geotechnical evaluation of the
site area?
o What hydrogeologic settings, if any, are particular-
ly suited to the location of hazardous waste manage-
ment facilities?
o What types of cap and bottom liner requirements are
appropriate for facilities in arid regions?
o What are the difficulties in siting a synthetically-
lined facility below the ground-water table?
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1.1.3 EPA Response
The EPA conducted an evaluation of the comments re-
ceived and designed a broad technical program to respond to the
principal issues identified. The program was organized to con-
solidate available technical information regarding liner design
and installation procedures and to develop the capability to
assess the fate and transport of ].eachate under various design
assumptions. In order to accomplish these objectives, data was
collected in the following areas:
o FML and clay liner design, installation, and main-
tenance procedures;
o Leachate characteristics and quality; and,
o Hydrogeologic fate and transport modeling;
The EPA developed the program using a phased approach.
Essentially, information was obtained from three perspectives:
research results, analytical modeling of facility performance,
and actual performance data from existing facilities. Using this
approach, EPA ensured the incorporation of current theoretical
information as we].l as realistic performance data. The resulting
information was evaluated to assess the practical performance
which can be expected from clay and synthetic liners at hazardous
waste management facilities assuming various design alternatives
and locational settings. The specific response to each comment
received was developed using the resulting information base. A
complete list of the significant comments received and the re-
sponse based on the results of this program are provided in an
Appendix to this report.
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1 .2 LINER PERFORMANCE CONCLUSIONS
The principal conclusions developed as a result of the
investigation of clay and synthetic cap and liner systems are
summarized in the following sections. The conclusions presented
provide the basis for the direct comparison of clay and synthetic
liners in hazardous waste management applications.
1.2.1 Clay Cap and Liner Summary
Clay materials can prOvide an effective barrier to
significant leachate leakage if properly designed, installed, and
maintained. However, all clay materials will permit some leakage
and therefore cannot be used to comply with the current liner
performance standards for disposal facilities. Sufficient ex-
perience is available to allow the construction of stable clay
barrier layers which are adequately protected from physical haz-
ards. However, due to the complexity associated with hazardous
waste management facility construction further refinement of the
methods of general clay barrier construction is required. Chemi-
cal hazards, posed by specific leachate types including concen-
trated acids and strong solvents, over long periods cannot be
adequately predicted using available testing methods. Finally,
the lack of current techniques to accurately measure installed
clay liner permeability raise further questions regarding the
present ability to predict clay liner performance in a hazardous
waste management facility.
1.2.2 Synthetic Cap and Liner Summary
Flexible membrane liner (FML) systems can be used
effectively to control leachate migration from hazardous waste
facilities. However, most synthetic liners will not achieve the
current facility containment goals expressed in the Interim Final
Land Disposal regulations. Well designed synthetic liners may be
penetrated by a very limited number of pinholes and small instal-
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lation holes, and may also leak as a result of vapor transport of
volatile leachate components through the liner systems. Properly
installed and tested synthetic liners will reduce the effective
leachate leakage rate to several orders of magnitude below that
obtainable through the use of well designed soil liners. Several
significant problems remain regarding the use of FML materials in
a hazardous waste environment. The most significant problem
remaining is the projection of the anticipated service life of
synthetic materials. Current experience provides a 10-year data
base for waste disposal applications and a 25-year data base for
other uses. Therefore, synthetic liner service life is currently
based in part on laboratory testing of the rate of change of
liner properties as a result of leachate exposure. Laboratory
test results for specific liner materials indicate potential
performance life of up to 50 to 150 years for some materials.
Conservatively, minimum expected performance life-times of over
25 years are indicated based on experience with FMLs for various
applications, as well as on available accelerated FML test re-
sults.
1.2.3 Cap and Liner Conclusions
In summary, FMLs offer a more effective barrier to
leachate leakage by several orders of magnitude. Clay liners
leak more than properly functioning synthetic liners, but appear
to offer longer stability due primarily to the substantial thick-
ness of installed clay liners in the absence of chemically reac-
tive leachate. Both synthetic and clay liners pose significant
installation complexities, although the problems associated with
each liner type differ significantly. Proper installation of
either liner type requires a high degree of precision and techni-
cal expertise and will require the use of formal quality
assurance procedures if reliability is to be ensured.
Reviewing the results of this study, it appears that
the properties of FMLS and clay liners are complementary. Clay
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liners prov2de additional stability and excellent bedding protec-
tion for synthetic liners. FMLs reduce overall leakage by sev-
eral orders of magnitude over that achievable with clay liners.
The combination of both liner materials would provide a superior
liner system with excellent leak prevention and stability proper-
ties. Based on the comparison of liner properties conducted, the
EPA may wish to consider requiring combiz:ation FML and clay liner
systems for most hazardous waste management facilities.
1.3 FACILITY/LOCATIONAL ANALYSIS
In the course of this analysis, a set of facility
designs/operational conditions, called facility settings, were
identified to represent the range of realistic designs and opera-
ting procedures. These facility settings were analyzed by means
of a computer program. Curves of leachate release versus time
were the primary output from the program for each facility set-
ting. Additionally, a set of hydrogeologic and climatic settings
were assembled, called locational settings, to represent broadly
the range of possible hazardous waste sites. Fourteen locational
settings were analyzed with analytical flow equations and seven
locational settings were analyzed by means of detailed fate
transport modeling. Hydrologic numerical models were used to
simulate fluid flow and contaminant migration in the unsaturated
zone and in the saturated zone.
The results of this overall analysis, even though it
must be considered preliminary, have led to the identification of
those facility and locational factors that ar important in
controlling the release and subsurface migration of leachate.
The most important facility factors, in order of impor-
tance, appear to be: facility type (landfills, impoundment,
etc.), climate, clay-liner permeability, type of FML failure
mode, and the presence and efficient operation of a leachate
collection and removal system. The major unsaturated-zone fac-
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tors identified are thickness of the unsaturated zone (depth to
water table) and the permeability of the unsaturated soil.
Although a number of saturated-zone parameters were determined to
be important, those that exhibited the gr test importance are
the permeability and thickness of the saturated sediment layer
and the position of the facility in the recharge or discharge
zone.
Comparison of the performance of seven locational set-
tings in the model simulations permitted a tentative rank ing of
the settings. Those settings most likely to limit the spread of
contaminants in th.g subsurface were found to be those having:
o Thick, low permeability unsaturated zone in combina-
tion with a low facility release rate;
o Low-permeability saturated sediment over a higher-
permeability bedrock located in a discharge zone;
o Thick, high-permeability unsaturated and saturated
sediments in combination with a low facility release
rate and a low hydraulic gradient; and,
o Thick, low-permeability saturated sediment in a
recharge zone.
Locational settings that are most likely to promote leachate
migration were found to be those having:
o Thin, high-permeability unsaturated zone in combina-
tion with high facility release rates;
o Thin, high-permeability saturated sediment in
combination with a recharge-zone location and
absence of an unsatarated zone; and,
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o Thin, high-permeability saturated sediment overlying
moderate to low permeability bedrock in combination
with a thin unsaturated zone.
From consideration of all the factors, the best com-
bined facility-locational settings would be those which combined
a low release rate with a locational setting involving: a thick,
homogeneous, low-permeability unsaturated zone; a thick, homoge-
neous and extensive low-permeability saturated zone; and, a good
retardation potential. The worst combined facility-locational
settings would consist of the opposite set of characteristics.
However, the vast majority of the possible sites in the country
fall’in between the extremes, and, thus, contain a mix of good
and poor characteristics. The current study revealed that for
some locational settings, it is not possible to distinguish among
the performance of the few facility designs analyzed.
The combination of a low-permeability sediment layer
and a discharge-zone location, or the combination of a semi-arid
climate and a thick unsaturated zone can mask potential perf or-
mance differences among landfill designs representing widely
different levels of leachate control.
The results of the study indicate that, in general,
locational factors and site acceptability are of greater impor-
tance than facility design and operation considerations. Selec-
tion of an acceptable site must come first. However, after the
acceptability of a site has been demonstrated, the protective
ability of the site and vicinity will de 3nd on the type of
facility design and operating procedures selected as appropriate
for the site and the expected waste stream.
1 • 4 RECOMMENDATIONS
The following provides a brief summary of the recommen-
dations developed during the course of this study in the areas of
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regulatory amendments, technical guidance, and the need for fur-
ther’ research. The recommendations provided are based on the
professional judgement of the hazardous waste experts involved in
this project.
1.4.1 Regulatory
The results of the investigation performed indicate
that some regulatory re-evaluation may be warranted. The princi-
pal regulatory amendments recommended include the use of a double
liner, composed of an FML and a clay liner, at disposal facili-
ties; modification of the allowable leachate level above FMLs;
and the incorporation of formal quality assurance requirements.
Other recommendations provided include several minor changes that
could be accomplished directly on the basis of avai) able techni-
cal information, such as clarification of the allowable “de
minimus” liner leakage rate and quantification of the terms
“short-term” and “long-term” performance goals. Several addi-
tional recommendations are provided that will require the comple-
tion of additional research prior to implementation. Possible
changes in the area of locational standards are provided, but
will require further research prior to implementation.
Any approach to the incorporation of location standards
in regulations governing hazardous-waste sites must establish the
goal of integrating facility design and operation with the loca-
tional setting. From the perspective of this st udy, locational
factors and site acceptability are of greater importance for
disposal facilities than design and c peration considerations.
However, once a site has been deemed acceptable, then the level
of environine.’ita. protection provided by the site and vicinity
will be based on the selection of facility design and operating
procedures suitable for the particular site and the expected
waste stream.
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o The objective of containing all leachate emanating
from hazardous waste management facilities during
the active life of the facility should be reviewed
to determine what “de minimus” leakage level would
be acceptable. The level of leakage allowed under
the “de minimus” concept should be set to the mini-
mum leakage expeced from well designed and con-
structed FMLs as well as for clay systems, indepen-
dently.
o A formal quality assurance program covering all
aspects of facility design, installation, operation
and maintenance should be required as part of the
permit process.
o Standard chemical resistance testing procedures and
criteria must be required for both synthetic and
clay materials. “Compatibility” must be defined.
o The requirement to limit leachate rise above the
liner to 30 cm should be modified to allow somewhat
higher leachate head levels for synthetic systems so
that greater protection of the leachate collection
and FML system can be provided. This would result in
minimal leakage increase because FML leak rates are
not primarily dependent on hydrostatic pressure.
Should combination liners be required, an increase
in the allowable leachate level would allow the
installation of a clay be&ing liner above the FML.
The 30 cm allowable leachate level should not be
modified for clay-only systems.
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o Removable coupons of the FML material used at a
particular facility should be required to be placed
in the leachate collection system to enable
verification of chemical resistance testing and
determination of continued FML integrity during
and following operation.
o Leachate levels should be monitored within the waste
management facility during operation and after
closure.
o EPA should consider requiring a double liner system
composed of a clay liner and an FML. The combined
properties of these two materials would signifi-
cantly improve the anticipated performance of cap
and liner systems at many hazardous waste mana ement
facilities.
o The closure period should be extended to allow the
installation of temporary caps in order to allow the
rate of waste subsidence to stabilize prior to in-
stallation of the permanent cap. Le chate cóllec-
tion must continue during this interim period.
o A hydrogeologic assessment of the facility area is
needed prior to permitting in order to provide the
necessary information to assess the fate and :trafls
port of leachate that might escape the facility.
o It is envisaged that two types of locational stan-
dards may be adopted. The first type would lnvolve
those standards for identifying clearly unacceptable
sites. These standards may be viewed as “rejecting
standards”. The second type of locational standards
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would aim to tpair up” each acceptable site with the
facility design/operation scheme most appropriate
for the climatic, hydrogeólogic and waste-stream
conditions.
1.4.2 Guidance Materials
The results of the liner and locational factor study
indicate that further technical guidance would prove beneficial
in several areas t& alleviate misconceptions and improve facility
performance. Recommendations regarding the preparation of addi-
tional guidance material are provided in the areas of: quality
assur ance of hazardous waste management facilities, the specif i-
cation of standard permeability and chemical resistance testing
procedures, and in the identification of specific hydrogeologic
factors of significance to facility design.
o Guidance material should be developed to standardize
chemical resistance testing of both clay and synthe-
tic liner materials. Standardization of testing
protocols, sample preparation, and representative
leathate is required, along with the development of
specific liner material acceptance criteria fo both
types of liner materials.
o Technical guidance should be developed regarding the
acceptability of various hydrological models, and
their appropriate use in the permitting process.
o Technical guidance specifying the minimum require-
ments of an adequate hydrogeologic site investiga-
tion is required. The investigation sh’uld inc1ud
areal density of borings, depth of borings, type and
level of information required from each boring, and
the nature and number of field arid laboratory tests
required.
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o A comprehensive quality assurance program should be
developed to support the permitting of hazardous
waste management facilities. The program may be
designed using other formal EPA quality assurance
progra ns as guidelines.
o For FMLs, additional guidance is requir d to stan-
dardize the use of current liner property testing
methods In projecting ultimate liner serviceability.
o Following the necessary research, guidance speci-
fying the acceptable equipment and procedures for
both field and laboratory testing of clay liner
materials, as well as a means to correlate the two
types of tests should be developed.
1.4.3 Research Recommendations
The results of the liner and locational investigation
indicates a strong need for further research regarding the per-
formance and durability of clay and synthetic liners in the
presence of hazardous waste leachate. The study also indicates a
need for significant further research in facility design modeling
and in the specification and importance of locational factors to
facility design. One of the principal objectives of this inves-
tigation was the identification of areas that are not presently
ur derstood and require further investigation. The following
provides a summary of the principal areas that should be investi-
gated. in support of future regulations and guidance.
o Further research is needed to develop appropriate
testing methods to verify the attainment of design
specifications of manufactured liner materials.
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o A central data base of chemical resistance testing
results should be established for both clay and
synthetic materials.
o Scientific cause-and-effect investigations and docu-
mentation of liner failure at well-designed faci-
lities should be conducted. Succ .ssful facilities
should also be thoroughly investigated.
o Further research is required to improve the standar-
dization of chemical. resistance testing procedures
to allow direct comparison of results between tests.
Research is needed both for FMLs and clay liners.
o An investigation of synthetic and clay liner proper-
ties is warranted to determine specific criteria for
liner chemical resistance determinations.
o Further investigation of the vapor transport mecha-
nism within synthetic materials should be conducted
to determine its significance for specific leachate
types and particular synthetic liner materials.
o Testing methods should be developed to allow liner
resistance monitoring at hazardous waste management
facilities during and after the operational phase of
the facility.
o A research effort should be conducted to ex’ mine the
stability of a conservatively designed waste manage-
ment facility in the presence of upward hydrostatic
for es. Such conditions could result in uplifting
and associated liner failure.
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o Further investigation of the design, construction,
and long-term performance of refined clay materials
for hazardous waste containment should be conducted.
Refined clays offer more homogeneous materials that
can be chemically tested more reliably than unre-
fined clay soils.
o Improved quality control tests for liners should be
developed and better correlation between test re-
sults and actual performance should be pursued.
o Development of more reliable techniques for detec-
ting subtle discontinuities in in-situ clays to
ensure their removal.
o Investigation of improved techniques and equipment
for uniformly distributing water in clay to develop
optimal moisture content.
o Development of improved methods of determining per-
meability both by field tests and by laboratory
tests for clay materials and installed liners.
o Assessment of the effect of dessication cracks on
the rate of infiltration through caps.
o Investigation of the thickness and characteristics
of bedding soil layers needed to protect FMLS.
o Chemical compatibility testing of solvents with clay
liners in single phase solutions comprised of mixed
organics in varying proportions with water is
needed.
o Polymer treated b ntonite should be tested for long-
term chemical resistance.
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o Further sensitivity testing of the HELP model is
required in order to estimate overall model accuracy
and reliability. Field verification of the model
may be warranted following the additional sensi-
tivity testing. Modification of the code is also
recommended so that the present assumption of free
drainage through the bottom liner is changed to
permit assignment of a range of possible soil pore
pressures beneath the liner.
o A complete evaluation of the system of hydrologic
models used to support this study is required in
order to improve the compatability and accuracy of
the various models used in subsequent assessments.
Consideration should also be given to the use of an
alternate integrated unsaturated-saturated hydro-
logic model for future analyses.
o Further investigation of other locational settings
is needed to provide information concerning the
sensitivity of facility performance to minor changes
in locational settings.
o The investigation of various complex locational
settings, which are frequently encountered in the
field, should be conducted.
o An investigation of various methods to estimate
regional recharge rates that are more consistent
with facility leak rates is required to support
subsequent modeling efforts.
o An investigation of the possible mouriding effects
that may occur at the saturated and unsaturated zone
boundary is required.
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o A detailed evaluation of the decay mechanisms that
affect hazardous waste components is needed to
assess the effective decay rate of these materials.
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2.0 INTRODUCTION
The Environmental Protection Agency was authorized
under the Solid Waste Disposal Act, as amended by Subtitle C of
the Resource Conservation and Recovery Act (RCRA) of 1976, to
establish a management system to safely treat, store, arid dispose
of hazardous waste. The EPA investigation of alternative regula-
tory approaches culminated in the publication of the Interim
Final Land Disposal regulations on July 26, 1982. Following
publication of these regulations, EPA established a 120-day corn-
ment period to allow interested individuals the opportunity to
address issues of concern. Based on the comments received and
technical issues identified within the EPA, a project was estab-
lished to collect available land disposal information, assess the
adequacy of the existing data base, and to compare various faci-
lity design alternatives and regulatory approaches. The program
was designed to provide a comparative data base to assess the
performance of flexible membrane liners (FML) versus clay liners
and to address the significance of locational factors in facility
design. This report provides a summary of the principal findings
of this investigation.
2.1 BACKGROUND
The comments received following publication of the
Interim Final Land Disposal regulations identified three major
issues regarding land disposal of hazardous waste: questions
concerning the potential use of clay liners for disposal facili-
ties; questions concerning ‘he long-term reliability of FilLs;
and, questions regarding the importance of locational factors in
facility design. The following section provides a brief descrip-
tion of the regulatory program, the principal comments received,
and the EPA project developed to respond to the comments re-
ceived.
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2.1.1 Part 264 - Interim Final Land Disposal Regulations
The published regulatory approach establishes design,
operation, and ground-water protection standards for the permit-
ting of hazardous waste management facilities. The basic design
and operating standards apply to all new surface iinpaundments,
waste piles, land treatment units, and landfills. The goal of the
design and operating requirements is to minimize the formation
and migration of leachate to the adjacent subsurface soil, ground
water, or surface water. This goal is achieved differently with
respect to different types of units. In this report, the design,
construction, operation, maintenance, and hydrogeologic siting of
surf a e impoundments, waste piles, and landfills are addressed.
The interim final regulations contain the following
major requirements for surface impoundments, waste piles, and
landfills. The regulations do not currehtly contain hydrogeo-
logic siting requirements. The requirements differ for disposal
facilities from those for storage facilities. Impoundments can
be used either as disposal or storage facilities; landfills are
used for disposal only; and, waste piles are used for storage
only.
o Each disposal facility, either impoundment or land-
fill, must have a liner that is designed to prevent
leachate migration into the liner; storage facili-
ties must have a liner designed to prevent leachate
migration through the liner during the active life
of the fa ility.
o Piles and landfills must have leachate collection
and removal systems (LcRS), as well as measures to
prevent run-on of liquids into the unit. The LCRS
for a landfill must be operated during the active
life of the landfill, and through the post-closure
care period.
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o Storage impoundments must have all waste and waste
residues either removed, decontaminated, - or solidi-
fied at closure. Piles must have all waste and
waste residues removed or decontaminated at closure.
o Disposal facilities must be closed by covering with
a cap that provides long-term minimization of liquid
migration through the closed facility. The cap must
be at least as impermeable as the bottom liner.
2.1.2 Significant Issues Identified by the Comments Received
The comments received following publication of the
Interim Final Land Disposal regulations identified several areas
that required further investigation. The comments received were
evaluated by the EPA and organized according to principal issue.
The following section provides a brief discussion of the issues
identified. A specific listing of the comments received and the
responses, based on the results of this study, is provided in the
Appendix of this report.
Performance of Cap and Liner Systems
Comments were received contending that clay liners
could be effectively used for containment at disposal facilities.
These commenters stated that clay liners are at least as effec-
tive as synthetic liners for containing hazardous waste. Further
comments were received regarding the expected performance life of
FMLs and the cvrrent ability to install acceptable FML seams in
the field. Other comments received relating to liner performance
include the following:
o The use of refined clays as a substitute for synthe-
tic liners.
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o The use of soil cement and admix materials in com-
bination with FML’s.
o The extent to which natural soils and clays act to
attenuate leachate.
o The need for liner inspection and quality assurance
programs.
o Ground water monitoring exemptions.
o The effects of various facility design specifics.
Leachate Release
Several commenters questioned the availability of field
techniques required during installation to determine clay and FML
permeability. In addition, questions were raised regarding the
one-foot leachate depth limitation within landfills.
Waste Compatibility
Questions regarding the chemical resistance of clay
liners and FMLs to various waste leachate streams were raised.
Specific information regarding the types of leachate that pose
the greatest risk was stated as being needed.
Liner Field Installation Problems
Several comments were received regarding the effective-
ness of available field installation techniques for synthetic and
clay liners and the need for a more comprehensive quality control
program. Specific questions regarding the installation of syn-
thetic liners addressed the following topics: field seaming,
field seam testing, material handling techniques, and the inter-
action of the liner with the leachate collection system. Ques-
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tions regarding clay liner systems addressed the following
topics: the measurement of permeability in the field, geotech-
nical site studies and compaction techniques.
Failure Modes - Bathtub Effect
The significance of failure modes, particularly “bath-
tub effect” failures, were the topic of several questions. Corn-
menters questioned the need for low permeability caps in arid
areas or for facilities located remotely :frorn all surface water
bodies. Similar comments were received regarding both clay and
FML cap systems.
Locational Factors
Numerous comments were received regarding the impor-
tance of locational factors to hazardous waste management faci-
lity design requirements. A brief summary of the major points
addressed follows:
o Should hazardous waste management facilities be
restricted from aquifer recharge areas and other
locations? What is the risk associated with loca-
ting facilities in various sensitive locations?
o Should the EPA require a minimum depth to ground
water below a facility?
o Should there be a minimum distance to surface-water
bodies?
o Is a geotechnical evaluation of the site area
necessary?
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o What hydrogeologic settings, if any, are particular-
ly suited to the location of hazardous waste manage-
ment facilities?
o What types of cap and bottom liner requirements are
appropriate for facilities in arid regions?
o What are the difficulties in siting a synthetically-
lined facility below the ground-water table?
2.1.3 EPA Response
The EPA evaluated the comments received and designed a
broad technical program to respond to the principal issues iden-
tified. The program was organized to consolidate available tech-
nical information regarding liner design and installation proce-
dures and to develop the capability to assess the fate and trans-
port of leachate under various design assumptions. In order to
accomplish these objectives, a data collection effort was ini-
tiated to gather available information from various research
programs, the liner industry, and existing facility operators.
Data was collected in the following areas:
o FML and clay liner design, installation, and main-
tenance procedures;
o Leachate characteristics and quality; and,
o Hydrogeologic fate and transport modeling;
The EPA developed the program using a phased approach.
Essentially, information was obtained from three perspectives:
research results, analytical modeling of facility performance,
and actual performance data from existing facilities, Using this
approach, EPA ensured the incorporation of current theoretical
information as well as realistic performance data. The resulting
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information was evaluated to assess the practical performance
which can be expected from clay and synthetic liners at hazardous
waste management facilities assuming various design alternatives.
The specific response to each comment received was developed
using the resulting information base. A complete list of the
significant comments received and the response based on the
results of this program are provided in an Appendix to this re-
port.
2.2 OBJECTIO’ES OF THE PROGRAM
The EPA initiated an extensive evaluation of currently
avail’able data on clay and synthetic liner performance and an
investigation of the importance of locational factors on facility
design. The study was conducted in three parts. The first part
was the investigation of all aspects of clay liner system design,
installation, and operation. Part two of the investigation in-
cluded a similar investigation of available information regarding
the anticipated life of synthetic liners (FMLs) within a hazar-
dous waste environment. The final part of the study included the
modeling of various facility designs, under various climate and
hydrog€o].ogic settings to determine the significant transport
mechanisms and ultimate fate of waste leachate after leakage from
a facility.
2.2.1 FMLs and Clay Liners
The first two parts of the EPA study provided a corn-
pärative data base for assessing the relative performance of clay
and synthetic materials. Primary emphasis was placed on the
evaluation of problem areas identified within the comments re-
ceived after publication of the land disposal reg.ilations.
Essentially, the investigation was designed to provide a practi-
cal assessment of liner performance in the following areas:
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o The adequacy of current liner design procedures;
o The adequacy of current liner installation proce-
dures;
o The need for more extensive quality ass jrance re-
quirements;
o The evaluation of chemical resistance testing
methods;
o The need for standard chemical testing procedures;
o The evaluation of the various failure modes asso-
ciated with liners;
o The evaluation of various design assumptions;
o The adequacy of the published regulatory program to
ensure the safety of hazardous waste management
facilities.
2.2.2 Locational Factors
The third part of the EPA program was designed to
provide an initial assessment of the significance of locational
factors with respect to the performance of hazardous waste man-
agement facilities. The program utilized various hydrogeologic
analysis models to project the impact of these facilities on
surrounding areas over a 200 year period. The analysis compara-
tively assessed the importance of the following lc.cational and
design factors to overall facility per ormance.
o The installation of multiple containment liners;
o The installation of leachate collection systems;
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o The significance of local climate;
o Facility cap design and placement;
o The importance of the water table depth below the
facility liner;
o The significance of the hydrogeoLogic-facility set-
ting;
o Aquifer characteristics and their importance;
o Facility proximity to surface water bodies; and,
o The importance of adequate post-closure care
procedures.
2.2.3 Specific Goals
The EPA investigation of liners and locational factors
was designed to provide a practical assessment of hazardous waste
facility performance. This objective required the evaluation of
the adequacy of the present regulations, available technical
guidance material, and a review of further research goals.
Specific elements of this project were developed to:
o Identify areas within the interim final regulation
that require further evaluation and possible revi-
sion;
o Identify areas of facility des. gn, operation, and
maintenance that r quire further technical guidance
based on available data; and
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o Identify those problems of hazardous waste disposal
technology which cannot be resolved based on
existing information and recommend research to
resolve these problem areas.
2.3 STUDY APPROACH
The EPA developed an overall study approach to incor-
porate both actual field information as well as research informa-
tion into the facility performance assessment. Data from exis-
ting facilities was obtained through personal interviews, review
of field reports, and the review of site investigation reports.
Research results were obtained using standard literature survey
techniques, supplemented by personal interviews with key re-
á archers in the hazardous waste field. Documented hydrologic
models were also used to assess the relative importance of
various facility design assumptions and locational settings. The
resulting data base provides a comprehensive summary of existing
information regarding hazardous waste facility performance from
the perspective of facility owners and operators, facility regu-
lators, and technical research experts.
2.3.1 Liner Evaluation Approach
The Environmental Protection Agency recognized the
fragmented nature of available information regarding clay liner
and FML systems and selected an approach designed to consolidate
available information from actual field experience, current re-
search efforts, and the evaluation of various liner design aiter.-
natives. Field data was obtained through interviews with regula-
tory personnel, facility operators, aiid liner construction spe-
cialists. A literature survey was conducted to provide research
results and professional perspective for incorporation into the
liner evaluation data base. Finally, the HELP model was de-
veloped and used to assess the relative meritE of various facili-
ty design alternatives. Overall, the approach selected consoli-
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dated available theoretical, field, and design information to
build a scientific data base to assess the advantages and disad-
vantages of various types of lined hazardous waste management
facilities.
2.3.2 Facility/Locational Analysis
This study represents the first major effort to assess
the overall significance of hydrogeologic loc4tional factors to
the design and performance of hazardous waste management facili-
ties. The method of study involved four aspects:
o Data compilation
o Identificatiopn of representative facility settings
and locational settings
o Selection of analytical and numerical methods of
analysis
o Selection of performance measures.
Data compilation was performed by EPA, the GCA Corporation and
Geraghty & Miller, and involved the collection and evaluation of:
information on facility design and operation; climatic data; and,
hydrogeologic data for representative areas of the country.
Representative facility settings and locational set-
tings were selected for analysis. For the purpose of this study,
a facility setting is defined as a specific combination of compo-
nents of a waste facility including specified permeability values
and other design f?atures, along with a specified set of opera-
ting conditions. A locational setting is defined as a specific
hydrogeologic domain and climate that encompasses the unsaturated
zone and upper saturated zone, and that includes a specified
subsurface flow system.
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Twenty-one facility settings were identified by EPA for
analysis under the study. These covered three facility types -
landfills and disposal and storage surface impoundments - and
included three climatic types and a range of design and operating
features affecting leachate generation, seepage and lateral
drainage. Fourteen locational settings were developed by
Geraghty.& Miller for the study using analytical flcw mbdels, and
seven we e identified specifically for detailed fate and trans-
port modeling. The locational settings differ from one another
primaril y with regard to: location of facility in a recharge or
discharge zone; average recharge rate; thickness of the unsa-
turated zone; relative thickness of the sediment and bedrock
comprising the saturated flow system; and, permeabilities of the
assumed sediment and bedrock units. Parameter values were speci-
fied in detail for each locational setting.
Several methods of analysis were utilized in the study.
EPA’s computer model HELP was used to estimate the release rate
of leachate through the bottom liner of each of the twenty-one
postulated facility settings. Curves of release rate versus time
were generated for each facility setting. The fourteen loca-
tional settings were evaluated by Geraghty & Miller using analy-
tical equations for flow in the unsaturated and saturated zones.
ANCO/Battelle, Pacific Northwest Laboratories performed fate and
transport modeling of the seven locational settings. In this
modeling effort, the computer program PRZM was used for flow and
mass transport modeling in the unsaturated zone. Output in terms
of conthminant loading at the water table was input into the
numerical model CFEST which was used to simulate flow and con-
taminant migration in the saturated zc ne in a 2—D vertical plane.
For each locational setting, the s. mulation period was 200 years,
and the resulting cuntaminant concentrations with respect to
certain performance measures were noted. In all cases, a con-
stant source concentration of 1.0 mg/l was assumed for the
leachate released from each facility.
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The interpretation of the results obtained was compli-
cated by the scope of the overall assessment and the lack of any
previous studIes in this area. The results are useful in making
conclusions about the relative importance of various locational
factors, but are not appropriate for use in an analysis designed
to predict ground-water contamination, or to assess other effects
resulting from various failure modes.
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3.0 COMPARISON OF CLAY AND SYNTHETIC CAP AND LINER SYSTEMS
The objective of the clay and FML studies was to pro-
vide a sufficient information base to al1 w the direct comparison
of expected clay liner and FML performance. In order to achieve
this goal, both studies were conducted using a similar, approach.
The following section provides a description of the general
approach used, and a detailed comparison of the significant
results obtained.
3.1 INTRODUCTION
The investigation of hazardous waste management faci-
lity cap and liner systems was conducted to examine the major
issues identified either by the comments received following pub-
lication of the regulations or internally within the EPA. The
effort was organized into five principal tasks for clay and
synthetic liners. Four of the tasks identified were identical
for both liner types. These included the investigation of fail-
ure mechanisms, installation problems, chemical resistance, and
the modeling of the efficiency of alternative design scenarios.
Permeability testing methods were investigated as the final task
for clay liners. For synthetic liners, the final task evaluated
was the investigation of expected liner performance and service
life. This approach provided a data base for direct comparison
of liner design, installation, and maintenance features for both
clay and synthetic liner materials.
The results presented for clay liner systems assume
that recompacted clay material was used. Similar problems would
occur using in-situ clay materials, however in many cases the
severit’ of the problems identified would be significantly great-
er for in-situ materials. The results presented apply to general
clay materials. The specific aspects of particular clays such as
bentonite or the use of refined clay materials have not been
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addressed in this report. Additional information regarding spe-
cific clay materials are provided in the supporting technical
project reports.
The resulting cap and liner information provides a
basis for further research efforts, the development of additional
technical guidance material, a td the evaluation of potential
regulatory revisions. It should be noted that the resulting
information base represents a preliminary base that, in some
areas, will require further development. Some of the conclusions
reached are tentative due to the lack of complete information
regarding several areas of liner technology, particularly in the
areas’of chemical resistance of liner materials to waste leach-
ate, the importance of locational settings, and the need for a
more comprehensive quality assurance program for hazardous waste
management facilities. The recommendations for further study
define a basic strategy for completing the liner data base deve-
loped during the course of this project. The recommendations
provided and the conclusions reached during the course of this
study are based in many areas on professional judgement rather
than sound scientific information due to the lack of adequate
facility performance data at this time.
3.2 ADVANTAGES AND DISADVANTAGES OF CLAY AND SYNTHETIC LINERS
This section provides a brief summary of the signifi-
cant advantages and disadvantages of each liner type. The re-
mainder of this chapter presents a summary of the significant
results of the study of clay and synthetir liners, and provides a
comparison of the various performance features of both types. A
more detailed description of the technical study results and the
investigative procedures used are provided in the following in-
terim project reports:
Interim I - Clay Cap and Liner Systems
Interim 11 - Synthetic Cap and Liner Systems
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3.2.1 Advantages and Disadvantages of Clay Liner Systems
The most important advantages of the use of clay
materials for the lining of nazardous waste management facilities
are:
o .A considerab’e base of information on clay barrier
design and construction experience is available;
o Clay minerals exhibit varying degrees of self-
healing capacity;
o Clay materials can be installed as a liner using
proven mechanical construction methods for place-
ment and compaction; however, verification of desig
specifications remains a significant problem;
o Clay minerals, when compacted under proper condi-
tions, can achieve low permeability (1O cm/sec);
and,
o Caps constructed of clay materials ‘ an be repaired
and/or replaced relatively easily using available
grading and compaction methods.
The most significant disadvantages of the use of clay
minerals for the lining of hazardous waste management facilities
are:•
o Chemical resistance of clay materials varies by
local cliy type and type of leachate in rather
complex and undetermined ways;
o The permeability of one portion of an installed clay
liner can differ considerably from the permeability
of another portion of the same liner;
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o Clay liners will always experience some leakage due
to their finite permeability, generally greater than
i0 7 cin/sec;
o Long-term effects of liner exposure to hazardous
waste leachate cannot be specifically d termined
using current techniques. Laboratory testing has
suggested that exposure to pure organic chemicals or
strong acids can drastically increase the permeabi-
lity of clay liners;
o Permeability of clay liners cannot be conveniently
measured in the field , laboratory procedures are
not standardized, and field and laboratory results
are not directly comparable;
o Clay liners are subject to desiccation (drying) and
as5ociated cracking;
o Since clay materials are naturally produced, wide
variations in physical and chemical properties occur
based on clay origin;
o Clay liners may be penetrated by burrowing animals
or root systems if unprotected; and,
o The attainment of design specifications during field
installation must be closely monitored or signifi-
cant changes in erformance can be expected.
3.2.2 Advantages and Disadvantages of Synthetic Liners
The following provides a brief list of the most signi-
ficant advantages of synthetic liners:
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o Leachate migration through intact FMLs is prevented
except for gaseous diffusion when certain wastes are
in contact with the liner. Non-volatile materials
can be completely contained;
o Since synthetic materials are manufactured they can
be formulated to exhibit uniform properties under
proper quality assurance control of the manufac-
turing process;
o Synthetic materials, can be selected to provide
flexibility, strength and chemical resistance
properties to meet specific hazardous waste facility
design requirements;
o Leachate leakage through synthetic materials is not
hydraulically driven and is not dependent on the
hydraulic pressure exerted by the waste material and
leachate, unless holes are present;
o The formulation and manufacturing of synthetic liner
materials is well understood, and the technology
required to produce uniform liner materials is
available. If proper precautions are taken, the
present technology is capable of successful liner
installation;
o Synthetic materials can be reinforced to provide
suff cient tensile strength to prevent failure due
to minor subsidence or soil movement; and,
o In service testing methods are available to allow
monitoring of synthetic liner materials during the
operational life of the facility. Monitoring tests
can be defined to reasonably approximate actual
liner conditions.
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Synthetic materials also have several disadvantages
that must be considered in the design of hazardous waste manage-
ment facilities. The most significant disadvantages of synthetic
liners with respect to their use in containment of hazardous
waste leachate are:
o Synthetic barriers are relatively thin membrane
liners that are susceptible to puncture, tearing,
and other types of penetration damage;
o Synthetic materials m y lose tensile strength if
stressed over long periods of time;
o Material properties of some FNLs are affected by
exposure to sunlight, ozone, fluctuating temperature
extremes, and fluctuating loads and pressures;
o The long-term effects of liner exposure to hazardous
waste leachate cannot be specifically determined
using current techniques. Laboratory testing has
shown that exposure to pure chemicals can result in
alteration of the physical and chemical properties
of synthetic liner materials; and,
o The short experience base available for FMLs
(10 years for hazardous waste applications, and
25 years for non-hazardous waste applications) does
not allow verification of liner life projections and
long-term performance goals.
3.3 EFFECTIVE LINER LEAKAGE
The evaluation of the effective leak rate of synthetic
and clay liners is critical to the assessment of liner perfor-
mance. The problem of leak rate testing in the field is compli-
cated by the lack of standard test procedures and the impractical
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nature of current test methods. Resolution of this problem
through further research is critically important to the question
of land disposal reliability and safety.
Leakage through clay liners and FMLs occurs via dif-
ferent mechanisms. Clay liners are essentially soil liners and
are permeable to aqueous leachates. Synthetic liners can be
impermeable to direct leachate leakage. However, installed FMLs
can be expected to have a limited number of pin holes due to the
manufacturing process used or as a result of a small number of
undetected installation mishaps. In addition, some leakage may
occur for specific volatile leacliate components by vapor trans-
port through an FMLS The actual vapor transport rate experienced
by an FML is a function of the composition of the waste material,
the specific interactions involved between the leachate and the
FML, and the rate of permeant removal by the soil below the FML.
At present, there is no established method that has been vali-
dated to determine the effective vapor transport rate through
FMLs in the field. In order to understand liner performance it is
important to understand the implications of gaseous versus liquid
mechanisms to liner leakage. The following section provides a
brief description of these mechanisms and their importance to
clay and FML performance.
3.3.1 Clay Liner Leakage
The permeability of clay liners determines the effec-
tive leak rate of the clay liner system. Other mechanisms may
result in minor leakage, but are considered insignificant when
compared to liner permeability leakage for dilute aqueous per-
ateants. Unfortunately, installed liner permeability cannot be
adequately determined using current laboratory testing me_hods or
available field testing methods. Several potential sources of
error have been identified in laboratory permeability tests for
both saturated and unsaturated clays. Of the possible sources of
error identified, the greatest concern is the use of samples that
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may not be representative of field conditions. Disturbed samples
that are taken for laboratory analysis and repacked in the
various types of apparati will not have the same fabric, struc-
ture, or pore configuration as in their undisturbed state, Addi-
tionally, the use of small samples compounds the problem by
omitting macroscopic variations occurring in the field, such as
sand lenses, fissures, joints, and root holes. Therefore, be-
cause laboratory tests are deficient with respect to monitoring
both microscopic and macroscopic features of in-situ soils, ex-
reme caution is necessary when using laboratory results to
project actual field conditions. Further development of alterna-
tive field testing methods that can be directly compared to
laboratory results is needed. Due to these problems researchers
have attempted to use v arious clay properties, which can be
measured easily, as indicators” ó f installed liner permeability.
The following liner parameters are generally used to verify
attainment of liner design specifications:
o Compaction
o Water content
o Density
The direct measurement of these parameters in the field
provides the best available method of field verifying attainment
of liner design specifications. Clay material selection for use
as a liner material requires a more detailed assessment of liner
characteristics and chemical 1 properties. In general , clay char-
acterization requires the evaluation of cation exchange capacity,
hydration characteristics, plasticity, and porosity. These para-
meters can be measured using available laboratory techniques to
support clay material selection for specific facility applica -
tions.
A fairly extensive base of laboratory and to a lesser
extent field permeability data exists for clay liner systems.
Due to the lack of standard testing procedures and protocols, the
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accuracy of this information base is less than desired. However,
from the review of the information base available, some general
conclusions can be reached. It appears that permeability rates
on the order of 1O cm/sec can be attained through the proper
selection, design, placement, and compaction of clay liner ma-
terials. Results that indicate lower effective permeabilities
for clay liners are considered optimistic, since laboratory re-
sults generally show lower permeabilities than actual field tests
due to sample preparation methods and the testing apparatus used.
It should be noted that permeability in the iO cm/sec range,
requires considerable compactive effort and testing during field
installation. Clay liner permeability of iO cm/sec should be
considered a lower limit to attainable field permeability.
3.3.2 FML Leakage
Leakage through FMLs occurs by inherently different
mechanisms than leakage through clay liners. This is due largely
to the fact that FML’s are thin membranes of long-chain organic
polymeric materials. Since FML’s are thin, they are subject to
puncture holes and installation damage such as faulty seaming.
Further, the chemical nature of the liner material lends itself
to other mechanisms of leakage such as vapor transport. FML
holes are discussed in further detail in Section 3.6, but are
included in this discussion since they must be considered as a
major component of synthetic liner leakage.
Vapor transport will occur through synthetic liners for
all volatile components of a leachate including water. Essen-
tially, this means that organic materials and water will diffuse
through a synthetic liner at some finite rate, while heavy metals
and other non-volatile inorganic materials will not. Basically,
vapor transport refers to the diffusion of gaseous vapor through
a liner material in response to a concentration gradient. There-
fore, the rate of leakage which occurs is not dependent on hy-
draulic pressure (depth of leachate) on the liner. Limited test
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results are available for vapor transport. Based on these re-
sults, vapor transport of pure chemicals in contact with a 30 mu
layer of high density polyethylene (HDPE) produced leakage in the
range of 1 2 to iO— 4 Kg/day/rn 2 for the specific organics tested.
Other FML materials indicated much higher transport rates. As-
suming leachate properties similar to water for comparison pur-
poses, this results in a leak rate ranging from a high of 10—8
to a low of 10 cm/sec.: These results were obtained under
conditions of maximum driving force and are not representative of
hazardous waste liner conditions. Based on the results evaluated
during the course of this study, vapor transport may result in
liner leakage on the order of 10 10 cm/sec for properly selected
FML ak d leachate combinations.
Holes may result from the manufacturing process (pin-
holes), faulty liner seams,: or punctures due to careless instal-
lation. Regardless of the mechanisms involved, a small number of
liner holes will be present in many FMLs. The significance of
liner holes to the assessment of overall leakage depends primar-
ily on the size of the holes present and the permeability of
underlying liner bedding materials. Hypothetically, a liner
which has an effective hole area of one square meter per acre
placed over a soil with a permeability of 1O 4 cm/sec would
result in net leakage of approximately 2.5 x io8 cm/sec. A well
designed liner system installed under an adequate quality assur-
ance program would achieve leak rates several orders of magnitude
less than this value. Therefore, leakage of 2.5 x i0 8 cm/sec
should be considered an unrealistically high upper bound for syn-
thetic liner leakage due to holes. Further substantial leakage
reduction would be achieved if the liner bedding material used
was less pervious than the value of i0 4 cm/sec assumed in the
hypothetical example. Clay bedding ci permeability io 6 cm/sec
would result in net leakage of 2.5 x 10—10 cm/sec.
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3.3.3 Clay and FML Leakage
Considering the effects of vapor transport and the
presence of pin holes in FML’s, the net effective leakage fron a
veil placed and designed FML would be less than 1O °cm/sec, if
the liner were properly designed, selected and inst lied over
well compacted fine clay-bedding material. Similarly, well dqs-
igned clay liners can be expected to achieve leak rates on the
order of iO cm/sec. Therefore, based on the results obtained
through this investigation it can be concluded that the use of
synthetic liners will reduce net. leakage from hazardous waste
management facilities by at least several orders of magnitude if
synthetic materials are properly selected and designed.
Further, since the presence of holes essentially con-
trols the effective leak rate of properly selected synthetic
liners, it would appear that installation of an FML over a clay
bedding layer would provide a significant improvement over either
liner material alone. This is particularly true since clay
provides an excellent bedding material for FML installation.
Various design alternatives were evaluated using the
EPA facility design model referred to as the HELP model. The
results indicate that climate factors are most important in
determining the amount of leakage from a facility, since precipi-
tation provides the basic driving mechanism for leachate genera-
tion and leakage. The facility cap and leachate collection
system provide the most important design features of landfills
for controlling facility leakage, because they control the hydro-
static head on the facility bottom liner. Leakage may be reduced
if FML’s are installed over a clay liner used as bedding material
for the FML. A determination o the effect of using an FML over
a clay system or vice versa was not conducted.
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3.4 CHEMICAL RESISTANCE OF LINER MATERIALS
The evaluation of the chemical resistance of clay and
synthetic liners to hazardous waste leachate is a comple . problem
requiring specific data as to the chemical components of the
leachate as well as the chemical structure of the specific liner
material selected. Clay liner materials exhibit widely varying
chemical properties depending on the type of clay selected and
the particular clay deposit excavated. Similarly, synthetic
materIals exhibit an enormous variation of properties due to the
polymer used and the specific formulation used in liner manufac-
ture. In addition, the specification of leachate components even
for relatively simple waste streams is extremely difficult if not
impossible. Given the essentially unlimited number of potential
chemical combinations available, it is basically impossible to
determine the specific resistance of a given liner material to a
specific waste stream leachate a priori . Therefore, the determi-
nation of the chemical resistance of a specific liner material to
a particular ].eachate requires direct testing of the leach-
ate/liner combination. The following section provides a descrip-
tion of the techniques available to accomplish this testing and
the reliability of the results for synthetic and clay liner
systems.
3.4.1 Chemical Resistance of Clay Liners
The evaluation of the permeability of clay layers in
the presence of leachate requires an understanding of the crys-
talline clay structure and its response to various chemicals.
Basically, clay minerals consist of silicates of aluminum and/or
iron and magnesium, arranged in patt&.rned layers with varying
degrees of water in betwe.. n. Some chemicals, particularly organ-
ic solvents and strong acids displace interlayer water in clay
materials, and can produce volume changes within the structure.
The net effect of these changes may produce either an increase or
decrease in the effective permeability of the clay. Test results
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are available for several classes of materials. In general, the
results indicate that little significant change in clay perrneabi-
lity will result from exposure to dilute organic materials.
However, significant clay permeability increases have been ob-
ser ’ed when clay is exposed to strong organic solvents such as
benzene and xylene or if clay is exposed to strong acid solu-
tions. The results obtained cannot be directly compated, since
procedures and testing equipment used varies by laboratory.
The base of available information regarding the chemi-
cal resistance of clay materials to hazardous waste leachate is
limited, since research efforts addressing this aspect of hazard-
ous w ste management have commenced only recently. Clay liner
resistance testing is currently accomplished using ordinary pe-
rmeation testing devices, adequately protected to prevent instru-
inent damage due to leachate contact. Permeability tests cond-
ucted for pure water and for leachate are compared to estimate
chemical resistance. In order to obtain a time relationship the
testing process is repeated at various time intervals following
exposure of the clay to the leachate. The results generally
indicate a rapid change in permeability, followed by a gradual
stabilization of clay liner permeability. However, specific
chemicals result in significantly increased clay permeability
after stabilization. This has been noted primarily for strong
organic solvents and concentrated acid solutions. An important
result of the research efforts conducted is the short period of
time required for permeability changes to become evident in a
test sample. The results available generally indicate that per-
meability changes occur after the passage of on]y one to two pore
volumes of permeant fluid.
3.4.2 ‘ themical Resistance of FMLS
The assessment of the chemical resistivity of synthetic
liner materials to chemical leachate is conducted indirectly and
the results obtained are subjectively interpreted. Basically, a
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sample of the liner material is tested in the laboratory to
determine it’s unexposed properties. The sample is then either
immersed in a representative leachate or the leachate can be
sealed within a liner material pouch and immersed in water. The
FML material is removed at various intervals and reanalyzed to
determine any significant change in properties which have
occurred. The testing protoco1 used are not standardized be-
tween laboratories and therefore the results obtained cannot be
directly compared. The EPA specified Method 9090 falls short of
the complete specification of test conditions since procedures to
maintain leachate bath temperature and levels are not specified.
The properties of synthetic liners which are used most
frequently as indicators of chemical resistance are: weight
change, dimensional stability and strength parameters. Weight
change provides a definitive indicator of the lack of chemical
resistance of a liner material. Unfortunately, the lack of any
weight change does not necessarily imply acceptable chemical
resistance of the liner. It is generally accepted within the
synthetic liner industry that a measured weight change of more
than 10 percent indicates that the liner is not sufficiently
resistant to the specific leachate tested. Changes ±n liner
strength parameters and the physical dimensions of the samples
are also used as indicators of chemical resistance, however no
generally accepted selection guidance is available.
The lack of synthetic liner testing acceptance criteria
requires the subjective evaluation of the significance of any
noted property changes by the researcher r laboratory involved.
Therefore, chemical resistance results are highly dependent on
the particular . .aboratory involved. Further, the lack of stan-
da dized testtng procedures essentially reduces the credibility
of the results obtained, because the tests cannot be repeated by
other laboratories for verification. The EPA Method 9090 proto-
col provides a firs’ step toward standardization but additional
effort in this area is warranted.
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The evaluation of available FML chemical resistance
testing ind icates that selected synthetic materials are suffi-
ciently resistant to specific leachate types. Further conclu-
sions cannot be developed, since most of the available chemical
resistence test data is considered proprietary and has not been
made public. Further, since FMLs have been used in.hazardous
waste managem nt facilities for the past 10 years only, the
extent o the existing chemical resistance data base is quite
limited. However, there have been no docuemented cases of FML
failure due to chemical degradation reported during this period.
3.4.3 Clay and FML Chemical Resistance
In comparing the available results from the chemical
resistance testing of clay and synthetic materials several ‘ 6iic-
lusions can be drawn. Both clay and synthetic materials appear
to provide chemically stable barriers to most dilute aqueous
leachates. Leachate from particular waste streams pose special
problems for most clay materials and some FMLs. Clay liners are
vulnerable to degradation due to exposure to many pure organic
chemicals, and are particularly vulnerable to strong organic
solvents and concentrated acids. Syv thetic materials can be
selected to specifically resist attack by organics, solvents, and
acids. However, a single FML material resistant to all types of
leachate has not been identified.
The test procedures used for testing both FMLs and
clays suffer from a general lack of protocol standardization, as
well as the absence of clearly defined chemical resistance accep-
tance criteria. As a result, available test results provide a
preliminary basis to project chemical resistance of various liner
materials to specific leachate components. Additional research
is needed to improve this information base to allow a more accu-
rate assessment of liner resistance to chemical attack in both
the ;hort- and the long-term. The available techniques are
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generally considered adequate to estimate the short-term resist-
ance of a specific liner material to a specific waste stream
leachate.
The test results available for clay liner materials
indicate that chemical resistance problems are evidenced early in
the testing program. This indicates that current testing proce-
dures can be used with some confidence to select suitable liner
materials. Particulary since the rate of change of permeability
recorded with the passage of one to two pore volumes of permeant
fluid generally represents the greatest rate of change recorded
during the complete testing program. The results available for
FMLsindicate that liner degradation may occur later in the
testing program, and in general once degradation commences, liner
decay continues throughout the testing program. This raises some
question regarding the length of FML testing needed to ensure
adequate chemical resistance of the synthetic material. In
either the case of synthetic or clay materials, these procedures
can be considered reliable in estimating liner resistance in the
short-term only.
The review of existing facilities and synthetic liner
installations did not indicate any cases of liner failure due to
chemical degradation. FMLs have shown excellent resistance to
chemical degradation in the field, but the period of record is on
the order of 10 years for hazardous waste applications and
25 years for other applications. More definitive conclusions
cannot be supported currently due to the lack of testing criteria
and standard prot icols. A double liner system using both an FML
and a clay liner appears to offer significant advantages over
either liner alone. Based on these results the EPA may wish to
consider the use of a double liner approach to improve the per-
formance of hazardous waste management facility liners.
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3.5 INSTALLATION PROBLEMS
The proper installation of the liner and cap systems
and supporting drainage, bedding and vegetation layers is criti-
cal to the performance of a hazardous waste management facility.
Most of the documented cases of facility liner failure indicate
tha’. faulty liner installation was a major factor in the ultimate
failure of the liner system. Current construction practices and
methods are available to properly install a liner system. How-
ever, the lack of strict quality control of the installation
process often results in weakened. liner systems. The problem is
similar for both clay liners and FML’s. The reason for this lack
of prbper control is not entirely clear. However, it may result
from a lack of awareness on the part of liner installers and
facility operators, as to the critical importance of proper liner
installation to overall facility performance.
3.5.1 Clay Liner Installation
The installation of an acceptable clay liner system can
be accomplished using available techniques of construction. How-
ever, the use of these familiar methods may not be sufficient to
maintain design specification tolerances required for hazardous
waste management applications. The most difficult aspects of
clay liner installation include the following principal tasks:
o Maintenance of a uniform moisture content within the
clay during placement and compaction;
o Placement of the clay material in uniform layers of
specified lift thickness; and,
o Attainment of the specified compactive effort and
the break-up of clods.
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Despite these problem areas, most of the problems asso-
ciated with clay liners at existing facilities result from the
lack of adequate quality control during the installation phase.
The most significant problem remaining is the specification of
adequate field tests to ensure the attainment of facility design
specifications.
The construction methods used to install clay liners
have been adapted from general soil conptruction methods; how-
ever, the ability of these methods to aqhieve the rigid specif 1-
cations required for waste management a plications has not been
completely verified. Hazardous waste applications require that
installed permeability exceeds some minimum value uniformly over
the entire liner area. This requires a uniform compactive effort
over the entire liner surface at optimum moisture and lift thick-
ness conditions. The problem is complicated further if the clay
material has not been properly prepared to remove clods and minor
quantities of higher permeability material. This is particularly
true if in-situ materials were used for liner construction.
A general consensus exists among liner experts that
acceptable liner installation should be verified through the
application of a comprehensive quality assurance program. Field
testing should be conducted to verify the attainment of liner
design specifications for liner moisture content, uniform lift
placement, and the achievement of compactive effort requirements.
Ideally, the installed permeability of the liner should be veri-
fied. However, methods to adequately measure permeability in the
field are not presently available. Present field techniques
provide results which cannot be compared to laboratory results
and are generally not practical due to the length of time re-
quired for testing. Further research is needed to deielop a
suitable field testing procedure to allow the determination of
installed liner permeability more directly.
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In addition, any liner installation will require the
completion of a detailed geotechnical investi ation of the site
and the preparation of a foundation design to accomodate antici-
pated loads during the life of the facility. Due to the impor-
tance of the facility foundation design a quality assurance
program should be required to verify attainment of design speci-
fications for proper compaction of all soil liners, subgrade
materials, waste materials, and the final cap system.
Most of the failures at existing facilities can be
traced to the lack of adequate quality control and assurance
control during facility design, installation, and operation. A
disti ict need exists for the requirement of formal quality assur-
ance controls during hazardous waste management facility develop-
ment. The required quality assurance program must address all
aspects of facility design, construction, and operation such as
liner placement, material testing, etc.
3.5.2 Synthetic Liner Installation
The installation of synthetic cap and liner systems
requires similar foundation and preparation as soil liners. In
addition to the general problems associated with waste facility
design and construction, proper installation of synthetic ma-
terials pose several unique problems which should be avoided.
Synthetic liners are relatively thin polymer barriers. Therefore
they are more susceptible to puncture, tearing and stress than
thicker soil liners. Special precautions must be taken to pro-
vide liner bedding material and protection from penetration by
vegetation and burrowing animals. These problems can be ade-
quately resolved using available techniques. However, a compre-
hensive quality assurance program is required to insure proper
application of the techniques required to insure attainment of
design specifications during the liner installation phase.
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FML installation includes an additional problem not
encountered in soil liner installation, that of liner seaming.
Liner seaming techniques vary depending on the liner material
selected, however, the basic procedure for all liner 4 pes is the
same. The liner panels are cleaned, the solvent or adhesive is
applied, the panels are pressed together, and allowfd to cure.
Major problems associated with field seaming are adverse weather
conditions including wind, rain, and cold temperatures. The
review of existing facilities indicated that most faulty seams
were attributed to the use of the wrong seaming adhesives and
cleaners. The results of this study indicate that reliable field
seams can be made if proper precautions are observed. A compre-
hensive quality assurance program is required to verify the use
of appropriate seaming materials and appropriate methods.
3.5.3 Clay and FML Installation
Based on the results of this study, it appears that the
proper installation of clay liners and FMLs can be accomplished
using currently available procedures. Clay liner installation
requires the use of basic foundation construction technology with
particular emphasis on uniform moisture content, lift thickness
control, and compactive effort. The installation of FMLs pre-
sents a different series of problems requiring emphasis on seam-
ing, installation of protective bedding layers, and the preven-
tion of construction and handling damage. Installation of FMLs
presents a more complex mechanical procedure due to the number of
interdependent tasks involved. Clay liner installation requires
fewer mechanical steps; but, they are more difficult to achieve
due to the need for complete uniformity over the entire liner
area.
In summary, available techniques can be used to install
stable clay and FML barrier systems. However, a comprehensive
inspection and audit program is required to ensure attainment of
design specifications. Proper installation of either a clay or
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synthetic liner within a hazardous waste management facility
requires strict adherence to precise installation procedures to
aachieve facility performance specifications. Clay installation
requires the attainment of uniform moisture content, compactive
effort, and lift placement within very tight specification
ranges. FML installation requires the completion of multiple
interrelated tasks, problems with any one of : ‘hich could result
in reduced liner performance. The application of a well, de-
veloped quality assurance program is essential in order to pro-
vide complete installation documentation and to attain system
performance obj ectives.
3.6 ‘FAILURE MODES
The liner investigation studies included a review of
documented cases of liner failure at existing facilities as well
as the evaluation of postulated failure mechanisms. The
facilities investigated were largely clay lined facilities;
however, a limited number of FML facilit9s were also reviewed.
The results indicate that subsidence represents the most critical
potential failure for synthetic and clay lined facilities.
Bottom layer subsidence was not observed at existing facilities,
however cap failure due to subsidence was noted at several
facilities. Cap failure results in the development of the
“bathtub effect” which can result in significant environmental
contamination of the facility area. Other failure modes have
been identified for both liner types and are briefly discussed in
the following sections. Essentially, the occurrence of facility
failures cannot be currently predicted, since the ultinrte fail-
ure mechanisms involved cannot be determined based on the inf or-
mation currently available.
3.6.1 Clay System Failure Modes
The most important clay liiier failure mechanisms iden-
tified include settlement and desiccation cracking. Settlement
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refers to problems associated with waste consolidation and poor
construction processes. Desiccation cracking refers to the vol-
ume reduction associated with some clay materials as water is
removed. Other mechanisms which may pose a problem include
piping, penetration, in-situ clay liner discontinuities, and
several miscellaneous mechanisms which present problems for spe-
cific locations or specific waste strea -’s, such as freeze-thaw
effects and gas generation. Penetration refers to the breaching
of a clay liner by burrowing animals and/or root penetration.
The problem has been observed at existing facilities, but is
generally viewed as primarily a management and maintenance prob-
lem. Other problems, such as earthquakes, floods, and other
natural disasters, can be avoided through proper siting of hazar-
dous waste management facilities.
Of the physical failure mechanisms identified, settle-
ment, and desiccation pose the greatest threat to clay liner
integrity. Researchers generally agree that these failure modes
can be controlled or eliminated through proper design, mainte-
nance and material selection. The remaining potential failure
modes including piping, penetration and special locational prob-
lems do not pose a significant problem to the development of
hazardous waste management facilities if they are properly ad-
dressed during the design, installation, and operation of the
facility.
The most significant problem encountered during the
evaluation of existing facilities was that of cap subsidence.
All waste materials can be expected to consolidate to some extent
as material decay progresses. Studies have shown that most
consolidation occurs during the first 5 years after facility
closure. proper wastø compaction during facility operation and
the placement of soil cover materials during all filling should
reduce the overall subsidence problem, but some subsidence can be
expected.
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The most critical failure mode associated with the
settlement problem is the development of the “bathtub effect”.
The “bathtub effect” can occur if the facility cap has a higher
permeability than the facility botthm liner. The rate of perco-
lation of precipitation into the facility may exceed the rate of
leakage through the bottom liner leading to a gradual filling of
the facility with leachate. If this situation continues, the
excess ].eachate will eventually overflow the facility resulting
in potential surface water contamination. The problem can be
avoided by insuring the integrity of the cap system and through
the use of a leachate collection system within the facility.
3.6.2’ FML Failure Modes
FMLs are subject to several failure modes which are
peculiar to synthetic liners in addition to subsidence problems.
Since FML5 are relatively thin polymeric materials they are
subject to pinholes caused by the manufacturing process, chemical
degradation, or punctures due to carelessness or faulty installa-
tion. The “bathtub effect” described for clay liners may also
occur with synthetic liners if the permeability of the cap system
is greater than that of the bottom liner as a result of subsi-
dence or presence of holes. A final failure mode which is pecu-
liar to FMLs is seam failure, which can result from the use of
inappropriate seaming materials or techniques for particular
synthetic materials. These problems can be avoided if proper
care is exercised during the manufacture and installation of
synthetic liners. Subsidence problems can be avoided through
proper design of the facility based on a thorough geotechnical
assessment of area c’ nditions.
Syntl’etic liner manufacturers have indicated that liner
pinholes can be avoided if proper precautions are taken during
the manufacturing process, however they are unwilling to guaran-
tee a pinhole free linei. Even with rigid quality control of the
manufacturing and installation process a very limited number of
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holes will remain in the liner system. The significance of the
presence of liner holes depends on the effective area of holes in
the liner and the permeability of the liner bedding material.
Thus, if an FML is placed o er a clay bedding material net leak-
age due to the presence of even an unrealistically large number
of liner holes would be minimized.
The “bathtub effect” was discussed under clay failure
modes, and poses a potential threat to synthetic liners as well.
Essentially, the “bathtub failure” may occur if the effective
permeability of the facility cap exceeds that of the bottom
liner. This may occur due to waste subsidence or simply due to
the presence of more holes in the FML cap than in the bottom
linet. The problem can be avoided by underlying the FML cap with
a clay bedding layer while attempting to minimize the holes
present in the cap using procedures defined earlier. Each of the
failure modes identified can be successfully avoided if proper
procedures are used to insure the attainment of design specifica-
tions for liner materials and construction processes. This re-
quires the use of a comprehensive quality control program to
verify liner specifications and installation techniques.
A properly designed, selected, and installed FML will
be subject to gradual degradation due to biological processes,
photochemical and oxidation mechanisms, and hydrolytic reactions.
Essentially, these natural mechanisms limit the maximum life of
an FML if all other failure mechanisms are successfully avoided.
Liner materials can be protected from photochemical and oxidation
effects relatively simply using pigmrntation and/or burial of the
material; however, this mechanism can degrade unprotected ma-
terials very rapidly. For a suitably proticted material, the net
effect oe the photochemical and oxidation mechanism has not been
determined, but no evidence of degradation has occurred in speci-
fic materials exposed over more than 30 years. Biological decay
occurs at the ends of the long chain polymers used in synthetic
liners. Biological decay mechanisms may have an effect over
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several hundreds of years. The migration of small molecules onto
the long chain polymers is referred to as hydrolytic or solvoly-
tic degradation. This mechanism may result in a measurable decay
effect in a few hundrei years. The significance of these natural
mechanisms on actual liner performance has not been determined.
However, these decay mechanisms would appear to establish an
upper limit to the anLicipated performance life of a well instal-
led, designed and maintained synthetic liner.
3.6.3 Clay Liner and FML Failure
The results of the investigation of existing facilities
indi ates that liner failure can be avoided if proper care is
exercised to verify liner properties and to install the system
properly. Most documented cases of liner failure can be traced
to faulty design and installation procedures. The most signif i-
cant problem which cannot be entirely avoided is the risk of cap
failure due to subsidence.
Clay cap systems which undergo subsidence can be re-
graded and repaired more directly than FMLs. Synthetic liners
are more difficult to repair once subsidence occurs because the
required removal of cover layers may result in additional FML
damage. The installation of a temporary clay cap over the faci-
lity during the period of substantial waste consolidation offers
one solution to this problem. Further, if the final FML cap is
placed over the graded temporary clay cap the resulting combina-
tion would minimize the potential for a “bathtub” failure.
The failure modes identified during the course of this
study can be avoided if a proper quality assurance program is
used to verify the facility construction phase. Both synthetic
and clay liner systems can be properly installed and maintained
to avoid the failures identified at existing facilities. Essen-
tially, t:echniques are available to avoid problems which result
in most types of liner failure. The problem reduced to providing
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a verifiable method of insuring that these procedures are used
during the facility construction phase as well as the operation
phase.
3 • 7 LONG TERM PERFORMANCE
The ojection of the long term performance of clay and
synthetic liners is a difficult problem. Essentially, the data
required to make such an evaluation is not available at this
time. The following sections provide a general summary of the
liner performance question, which is based partially on profes-
sional judgement rather than a completely reliable scientific
data’ base.
3.7.1 Clay System Performance
The experience base available for the installation of
clay liners for water retention purposes is relatively extensive.
However, further refinement of these construction methods is
needed to achieve the more rigid design specifications imposed on
liner systems for hazardous waste management facilities. Parti-
cular areas that will require further development are the techni-
ques to achieve and verify uniform liner moisture content, lift
thickness, and compactive effort. The significance of this lack
of suitable construction methods for attaining required design
specifications cannot be determined based on the information
currently available. However, this problem raises some question
regarding the long term performance of presently installed liner
systems.
Clay liners used for hazardous waste applications are
also subject to chemical attack by the waste leachate. The
mechanisms involved were briefly discussed in Section 3.4. Cur-
rently used chemical resistance testing methods, although not
fully standardized, provide a subjective measure of the resist-
ance of a particular clay material to a specific leachate in the
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short term. The available test results indicate that chemical
degradation of clay materials is evidenced early in the testing
procedure, after passage of only one to two pore volumes of
leachate. Further, the results indicate that the maximum rate of
change of clay permeability also occurs early in the testing
program. Therefore, the results of chemical resistance testing
of clay materials can be regarded as a conservative indicator of
the chemical resistance of clay liners. While serious questions
remain regarding the actual permeability of exposed clays, cur-
rent testing methods can be used to demonstrate either the re-
sistance or lack of chemical resistance of specific clay ma-
terials to a specific waste stream leachate in the short term.
Unfottunately, the techniques currently used are designed for
short-term permeability projections, extrapolation of these re-
suits to project long-term permeability cannot be justified on
the basis of available information. Techniques designed to de-
tect subtle changes in the crystalline lattice structure of clay
materials should be developed to assess long-term clay perfor-
mance.
The discussion presented is based on the assumption
that a comprehensive quality assurance program is observed during
the testing and construction of clay liners. The quality assur-
ance program must include evaluation of all aspects of the site
selection, geotechnical site evaluation, facility design, faci-
lity construction, facility operation, and liner maintenance pro-
grams. The critical nature of the liner system and the com-
plexity of its design and installation requires a comprehensive
qualit’ control program to insure that all aspects are completed
in accordance with facility specifications and can be verified
through independent audit.
3.7.2 Synthetic Liner Performance
Actual experience with FML materials covers a period of
only 25 years, experience with FMLs in hazardous waste applica-
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tions spans a period of only 10 years. FMLs are subject to
several problems unique to this type of liner material, primarily
due to liner thickness. Procedures have been developed to con-
struct acceptable FMLs if proper precautions are taken to protect
the liner material. Essentially, most of the procedures used in
FML installation are adapted from clay liner installation proce-
dures. These procedures are sufficiently advanced to insure
proper installation to avoid liner subsidence, compaction of
bedding and drainage materials, etc., if adequate quality control
is provided. However, procedures to deal with the :peculiar FML
liner problems have not benefitted from previous clay experience,
and therefore can be expected to undergo further refinement and
imprdvement as experience with synthetic materials increases.
The evaluation of the chemical resistance of synthetic
liners to leachate attack represents a second area of critical
concern regarding FML performance. The testing procedures used
were discussed previously, available test results in the public
domain are extremely limited and do not support meaningful con-
clusions. However, general results and interviews with experts
can provide insight into the significance of the chemical resis-
tance problem. Synthetic liner testing indicates that liner
degradation does not show a similar pattern to clay permeability.
Essentially, degradation is a gradual process which results in
the development of a monotonical].y increasing FML leak rate with
time. Therefore, short term testing results do not provide a
rapid worst case assessment of liner leakage potential. Testing
must be conducted over long time periods of several years in
c:der to provide a realistic assessment of the degradation rate
of FMLs. Fortunately, synthetic materials have shown a high
resistance to chemical decay in general, since there have been no
documented cases of liner decay recorded over the 13 years FMLs
have been used in waste applications. However a 10 year ex-
perience base is not sufficient to demonstrate long-term synthe-
tic liner performance. Researchers have attempted to extrapolate
short-term test results to project long-term performance. Projec-
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tions range from several years to more than 150 years, but there
is no generally accepted method of verifying these subjective
estimates. A minimum length of service for synthetic materials
can be conservatively estimated at 25 years based on current test
results. Service life projections of up to 50 to 150 years have
been indicated by the test results obtained for specific synthe-
tic materials. -
The estimating of synthetic liner performance is a
complex problem, since liner performance is dependent on proper
liner selection, installation and cthemical resistance testing.
These areas are relatively new, requiring unique construction
proc dures, non-standard laboratory techniques and particular
material handling procedures. Some of the problems can be avoid-
ed using procedures developed to prevent clay liner subsidence
and other construction problems. However, other areas must rely
on the use of recently developed methods which cannot be comple-
tely verified due to the current lack of sufficient experience
with synthetic liner materials in hazardous waste applications.
The complexity of the selection and placement of synthetic lin-
ers, and the use of recently developed, unfamiliar techniques to
accomplis)’ synthetic liner placement pose a significant risk to
ultimate liner performance. In order to minimize this risk an
extensive quality control program is required to verify the
completion of all steps necessary to select and install suitable
liner materials. The required quality assurance program must be
designed to verify the proper completion of each installation
step in the proper sequence to insure the overall integrity of
the PML system.
3.7.3 Performance Improvement Projections
The recommendations provided for improving anticipated
clay and synthetic liner performance are based on the assumption
that all systems should be geared toward preventing facility
leakage. Once leakage occurs corrective action is extremely
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difficult and expensive. The following provides a list of the
principal recommendations (a detailed discussion of each is pro-
vided in Section 5.0) made to improve liner performance:
o Implementation of a comorehensive quality assurance
program;
o Strengthening of cap design and maintenance require-
inents;
o Leachate level monitoring within landfills;
o Increasing leachate level restriction for FMLs;
o Standardization of chemical resistance testing
procedures and acceptance criteria; and,
o Consideration of requiring combination FML and clay
liner systems.
These recommendations were based on a subjective
assessment of the significance of various potential liner failure
mechanisms. The results of this assessment indicates that faci-
lity cap failure poses the greatest risk to facility performance,
if the selected liner materials are chemically resistant to the
specific leachate within a facility. Subsidence poses the great-
est threat to facility cap systems for both FMLs and clay
liners. In fact, subsidence cannot be entirely avoided, but it
can be minimized. Therefore, facility performance in the absence
of chemical decay can be significantly improved by providing
various backup systems to detect cap failure and remove leachate
before bottom liner failure occurs. D. 1 .rect leachate monitoring
within the facility would provide the required early warning of
cap failure. An adequately designed leachate collection system
would provide essentially a relief mechanism to prevent bc.ttorn
liner damage while cap repairs are effected. Further, should the
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leachate collection system fail, leachate level monitoring would
provide sufficient warning to allow the use of alternative leach-
ate removal strategies such as direct pumping, etc. The added
difficulty of installing appropriate leachate level monitoring
wells appears justified, since the review of documented failure
cases indicated that cap failure was a significant factor in most
cases reviewed.
Chemical resistance evaluation represents a second
major threat to facility performance. The information base
available for clay and synthetic materials is insufficient to
provide an adequate margin of safety to allow conservative esti-
mati n of long-term liner performance. Clay liners are more
easily tested because worst case conditons appear early in the
testing program, therefore clay systems are considered more
stable at least in the short-term. The worst case conditions for
synthetic materials are more difficult to determine, since they
may appear after several years of liner exposure, which is not
adequately reflected by current testing methods. Standardization
of testing methods and acceptance criteria is recommended in
order to allow verification and comparability of test results.
Further, disclosure of test results conducted using standard
methods is required to establish a substantial base of chemical
resistance data in the public domain. Until further standardized
information becomes available accurate long-term liner perfor-
mance projections cannot be developed, for either clay or synthe-
tic liners. Current service life projections are subjective
evaluations based on a very limited amount of scientific data.
Due to the uncertainty involved in hazardous waste
facility design and construction and due to the need for all
components to function as an integrated system, comprehensive
quality assurance control is absolutely essential to facility
performance. The liner represents only one part of the entire
facility structure. The performance of the lifler system is
dependent on proper liner selection, maintenance and
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installation; but is also dependent on the proper performance of
other facility components. Therefore, each significant component
of the entire facility must be regarded as critical to facility
performance. Quality assurance provides a mechani 1 i for
inspecting and verifying the proper functioning of each facility
component.
Assuming that the listed recommendations are accepted,
a subjective evaluation of anticipated liner performance can be
made. Synthetic liners can be expected to perform as designed
for a minimum period of 25 years, followed by a gradual decline
in performance over an extended period depending on the particu-
lar Waste leachate/liner combination used. How this relates to
the prevention of migration is unknown because the ultimate cause
of FML failure is unknown. Clay system performance over the
long-term has not been quantified, since degradation mechanisms
involved such as subtle chemical changes, eventual erosion, and
vegetative penetration after the post-closure period cannot be
adequately assessed. The actual performance period for clay
systems cannot be specified, but it is expected that the perfor-
mance period for clay liners may exceed that for synthetic
materials.
Without implementation of the liner installation and
selection recommendations, anticipated performance for either
clay or synthetic liners cannot be projected. Poor liner selec-
tion techniques could result in the immediate degradation of clay
liners due to chemical interaction and similar destruction of
synthetic materials over very brief time periods. Similarly,
poor field installation practices, which are not identified by a
quality assurance review can be expected to result in immediate
facility leakage. The imp oper compaction or placement of clay
materials will result in an unacceptable in-place liner perme-
ability. Improper installation and seaming of FMLs can result in
liner tears, puncture due to improper bedding, etc., resulting in
increased leakage. Essentially, without proper quality control
• 3—32
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and documentation, liner performance is undetermined. Reputable
designers and liner installers would be expected to do a rela-
tively adequate job of installation; however, the lack of consis-
tency between the various facility components would j.ncrease the
risk of failure significantly, particularly for FML systems.
Therefore, facility performance cannot be realistically projec-
ted, without proper quality control and construct on docuxnenta-
tion.
3.8 FML AND CLAY LINER CONCLUSIONS
The results of this investigation of clay and synthetic
linex’s provides a subjective basis for the comparison of the
significant advantages and disadvantages of the use of either or
both liner types for hazardous waste containment. The investiga-
tion has served to identify areas that require further research
in order to quantitatively assess liner performance. In addi-
tion, the results have identified areas where the developernnt of
further technical guidance is warranted. Finally, areas of the
current Interim Final Regulations which require re-evaluation
based on the results of this study are identified. The conclu-
sions reached are tentative, based solely on the investigation
performed, the evaluation of specific facilities and information,
and on the judgement of liner experts. The following provides a
summary of the results of the comparison of clay liners and FMLs
based on the results of this investigation.
Basically, properly designed and installed synthetic
liners will reduce the leakage from hazardous waste manag rnent
facilities below that achievable with well designed and construc-
ted clay liners by several orders of magnitude. Minimum expected
leak rates for clay materials are on the order of iO cut/sec,
while for FMLs maximum leak rates expected would be on the order
of 1O 0 cm/sec. Therefore, synthetic materials provide a signi-
ficant advantage over clay liners to prevent leakage.
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Problems exist in projecting the length of service
anticipated for both clay and synthetic liner materials. Data
available for FMLs indicates a conservatively estimated minimum
life of 25 years. Other less conservative escimates for specific
liner materials indicate service lives of up to 50 to 150 years.
The expected service life of clay materials cannot be- estimated
because long-term chemical resistance of clays has not been
projected. However, in the absence of chemical decay the added
thickness associated with clay liners would indicate a relatively
long-term stability of the liner system.
Finally, the construction techniques used to install
and niaintain clay liners are relatively well known, requiring
methods familiar to the industrial construction industry. How-
ever, further development of these techniques is required to
achieve the strict design specifications required for hazardous
waste liner performance. Synthetic liner design and installation
requires the use of additional field procedures that are not
completely developed due to the lack of an extended experience
base with these materials. Further, the added tasks of seaming
FMLs and providing sufficient liner protection from underlying
materials and construction activity, provide other areas where
problems can occur. In either case, experienced industrial liner
installaters must be used if an effective liner installation is
to be achieved.
In summary, FMLs offer a more effective barrier to
leachate leakage overall. Clay liners leak more than properly
functioning synthetic liners, but appear to offer lc ger stabi-
lity than FMLS. Synthetic liners pose additional mechanical
installation complexities o rer clay liner installation, therefore
the risk of faulty installation of FMLs may be slightly greater
than that for clay liners.
Reviewing the results cf this study, it appears that
the properties of FMLs and cla ’ liners are complementary. Clay
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liners may provide relatively long-term stability and excellent
bedding protection for synthetic liners. FMLs reduce overall
facility leakage and resist chemical degradation. The combina-
tion of both liner materials would provide a superior liner
system with excellent leak prevention and stability properties.
Based on the comparison of liner properties conducted, the EPA
may vish:to consider requiring combiflation FML and-clay liner
systems for most hazardous waste management facilities.
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4.0 SIGNIFICANCE OF FACILITY. AND LOCATIONAL FACTORS IN
MINIMIZING OR PREVENTING GROUND-WATER CONTAMINATION
In the course of this analysis, a set of facility
design/operational conditions, called facility settings, were
identified to represent the range of realistic designs and opera-
ting procedures, and were anal 4 ’zed by means of the computer
program HELP. Curves of leachate release vs. time were the
primary output from the program for each facility setting. Addi-
tionally, a set of hydrogeologic and climatic settings, called
locational settings, were assemb’ed to broadly represent the
range of possible hazardous-waste sites. Fourteen locational
settiflgs were analyzed with analytical flow equations and seven
locational settings were analyzed by means of detailed fate and
transport modeling. The model PRZM simulated fluid and contami-
nant migration vertically downward in the unsaturated zone, while
the model CFEST was used to simulate mass transport of chemical
contaminants in the saturated zone under assumed steady-state
flow conditions.
The facility/locational analysis resulted in the iden-
tification of the primary facility and locational factors affec-
ting the extent of leachate release and migration. Moreover, as
a specific set of facility design/operational schemes (facility
settings) and cliznatic-hydrogeologic conditions (locational set-
tings) were analyzed, tentative ranking of those facility set-
tings and locational settings was performed with respect to their
anticipated performance. To a limited extent, it was also pos-
sible to determine the nature of the relationship between faci-
lity settings and location settings.
This section represents a brief summary of the results
of the facility/locational analysis. More detailed information
is available in Interim Report III - Facility/Locational Analy-
sis, an interim project report prepared for EPA in July 1983.
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4.1 FACTORS AFFECTING MIGRATION RATES
4.1.1 Facility Factors
The impact of different facility factors, on the fate
and transport of leachate in the subsurface and local ground-
waters, hinges solely on the individual and combined effects of
these factors upon the rate and timing of ].eachate release
through the bottom liner.
On the basis of the particular facility settings iden-
tified in this study and the analysis that was performed, the
folldwing facility factors are important in affecting the magni-
tude and patterh of leachate release:
o Facility type: landfill, disposal surface impound-
ment, storage surface impoundnientg etc.
o Climate
o Permeability of clay liners and caps
o Thickness of clay liners and caps
o Failure mode assumed for FMLs
o Presence of a single liner versus a double bottom
liner
o Presence or absence of a leachate collection system
o Efficiency of leachate collection system
Not only the magnitude of the peak release or the long-
term release r&te, but also the timing and duration of the re-
lease can have a profound effect on ]eachate migration and at-
4—2
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tenuation in the subsurface. In this regard, the type of faci-
lity is important. Other factors being equal, for example, the
release rates of surface impoundments during the operational
period tend to be significantly higher than those from landfills.
Such higher initial rates can serve to speed the movement of
leachate through the unsaturated zone to the water table. After
closure, the leachat release rates for disposal surface impound-
ments tend to approximate those for landfills over the same
period, while no leachate is generated with storage surface
irpoundments as all waste in this case is removed at closure.
Climate is an irnportat t factor in determining the
amount of leachate generated by a facility. The major influences
here are annual rainfall and evapotranspiration. The analysis
showed that the leachate released from landfills of identical
design was significantly less in semi-arid climates compared to
moist-humid climates. For example, a particular design landfill
in a New Orleans-type climate released leachate at a rate four
times that for the same design landfill in a Denver-type climate.
For a given facility type and climate, the permeability
of the clay liners (if any) utilized in tha design is the most
important facility factor. In two locational settings studied,
increasing a landfill’s clay-liner permeability from 10 7 to
i C ’ 6 cm/sec resulted in a five-fold increase in the peak and
steady-state release rate. This magnitude difference exceeds
most differences related to changes in FZ4L failure mode.
Due to a lack of fj’ ld or laboratory data on the timing
and extent of possible FML failures, it was necessary to assume
various modes of failure for the purpose of performing the faci-
Jity/locational analysis. The particular failure mode assumed
for FML-lined facilities is crucial in determining whether or not
FML-lined facilities perform better than those with clay liners.
FML-lined facilities that were assumed to fail catastrophically
at some point - - 25 to ¶50 years from start-up —- ultimately
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performed no better, or slightly worse, than comparable clay-
lined facilities. While, FML-lined facilities that were assumed
to have a low constant seepage showed release rates that were
50 percent or less than those for comparable clay-lined facili-
ties where the clay permeability was i0 cm/sec.
The resence of an efficient leachate collection system
is an important factor in limiting the release of leachate from
landfills and waste piles. The study showed that for one faci-
lity setting, by continuing the operation of the leachate collec-
tion system beyond the post-closure care period for an indefinite
period, the peak release rate is reduced by about 45 percent,
compared to the case where the collection system is assumed to
stop operating at the end of the post-closure care period.
4.1.2 Unsaturated-Zone Factors
The primary factors that affect the rate and timing of
leachate migration through the unsaturated zone include:
o Depth to water table (thickness of unsaturated zone)
o Permeability of unsaturated-zone soil
o Porosity of the soil
o Initial moisture content of the unsaturated soil
o Retardation properties.
For a given facility release rate, the depth to the
water table is the most significant factor affecting the time for
the wetting front, and, hence, leachate, to traverse the unsatur-
ated zone to the water table. The thicker the zone, the longer
the time required for a contaminant to reach the water table.
Also, the thicker the zone, the greater the likelihood that
attenuation will occur by means of dispersion and that retarda-
tion will occur. In this study, locational settings were inves-
tigated that had unsaturated-zone thicknesses ranging from essen-
tially zero to 154 feet.
iEftec! 4—4
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The factors of permeability, porosity and initial soil-
moisture content of the unsaturated soil taken together affect
the rate at which water/leachate will move through the zone.
Permeab .lity and the initial soil moisture are directly related
to the rate of movement; that is, the higher the permeability and
the initial soil moisture, the faster the wetting-front movement.
Increa ing the average porosity tends to slow the rate of wet-
ting-front movement, because the capacity of the soil, to hold
moisture above the vetting front is thereby increased. In this
analysis, the initial soil moisture content was assumed to be at
field capacity for all cases, and the saturated permeability of
the soil above the water table ranged between lO 6 and
10_i Cm/sec, depending on the locational setting.
Retardation properties include properties such as cat-
ion exchange capacity and more general physical adsorption af fin-
ities. Certain types of clay minerals and soil organic matter
are known to have significant retardation properties for specific
mineral cations and for certain classes of organic molecules. As
presently understood, the process of retardation primarily acts
to delay the arrival of a contaminant at, for example, the water
table. For the case of a continuous and constant leachate
source, no reduction in the magnitude of the maximum concentra-
tion can be expected. However, for short-duration releases of
leachate, in addition to the effect of delay, the peak concentra-
tion will also be reduced. Retardation properties are generally
measured in terms of the soil-water partition coefficients (kds).
This coefficient is a function of both soil material and contami-
nant propertier and can vary over as much as five orders of
magnitude. The higher the kd value, the greater the retardation
of a chemical species, i.e., the lower its mobility in the parti-
cular soil material. In this study, two levels of retardation
were investigated: kd 0.2 mug (representing a high-mobility
species) and k 6 = 5.0 mug (representing a low-mobility species).
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4.1.3 Saturated-Zone Factors
The primary factors that affect the rate of leachate
migration and contaminant attenuation downgradient in the
saturated zone include:
o Permeability of the uppermost sediment layer
o Thickness of the sediment layer
o Relative permeabilities of the sediment layer and
the underlying bedrock
o Hydraulic gradient
o Retardation properties of the saturated zone
o Position of the facility in a recharge zone or
discharge zone
o Stressing an aquifer by pumping.
In the present study, only a limited number of cases
could be considered, and it was decided to investigate the effect
of the factors of permeability and thickness by utilizing values
representing nearly the extremes of their likely ranges. The
results indicate that the permeability of the uppermost saturated
sediment layer is probably the most important factor affecting
travel ti ie to downgradient points, including stream-discharge
points. The greater the permeability, the faster the rate of
flow.
When a low-permeability sediment layer overlies a mod-
erately permeable bedrock, slow vertical movement through the
sediment layer to the bedrock dominates over lateral flow in .the
upper layer. In this case, the thickness of the sediment layer
4—6
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directly affects the time taken for leachate to reach the bed-
rock. For cases involving a high-permeability sediment lay&,
lateral flow predominates, and increasing the thickness of the
saturated portion of the sediment layer will increase the amount
of dilution a leachate plume will experience. In this study,
sediment permeabilities considered were and 10_i cm/eec,
while bedrock perineabilities were lO 8 and 5 x 10 cm [ sec. The
saturated thickness of the sediment was assumed to fall either in
the range 10 to 30 feet or in the range 100 to 730 feet.
Hydraulic gradients are an important factor, as the
higher the gradient the greater the expected ground-water veloci-
ties.’ However, lateral gradients that tend to produce lateral
flow were found in this analysis to be significant only for those
settings with high-permeability (i0 cm/sec) sediment material.
Retardation properties for the saturated zone have similar
effects as those described previously for the unsaturated zone.
The same levels of retardation were studied in the saturated zone
—_ lcd of 0.2 and kdof 5.0 mi/gm.
The location of the hazardous waste management facility
with respect to the ground-water recharge or discharge zone can
be an important factor. A major effect of placing a facility in
a recharge zone is that there is an increased opportunity for
dilution. The disadvantage is that there is correspondingly the
likelihood that contamination may spread through dispersion over
a relatively large volume of saturated sediment or bedrock. A
discharge location for a waste management facility is charac-
ter.zed by vertical upward movement of water in the sediment and
underlying bedrock. This tends to trap a portion of the leachate
in the upper part of the sediment, which is beneficial. However,
this upward movement could bring contaminated ground wi”ter to the
ground surface in areas adjoining the site and result in surface
water contamination.
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Stressing an aquifer consists of pumping from wells,
galleries, etc., that tap the aquifer. Stressing the saturated
sediment layer or the underlying upper bedrock results in in-
creased rates of migration of hazardous constituents in the
direction of the well being pumped. However, significant dilu-
tion can also occur at the well as a result of eater being
brought into the well train directions other than that from which
the contaminant is coming.
4.1.4 Factors Not Examined
The hydrogeologic factors not considered in the present
analysis include:
o Inhontogeneities and Anisotropy
o Sediments with very low perneabilities
o Hydrogeologic complexity.
In the present analysis, each geologic layer was
assumed to be homogeneous and isotropic. The term homogeneous
implies that the material properties were assumed to be every-
where the sate within each layer. Isotropy refers to the assuinp-
tion that permeability is the same in all directions. Under most
natural conditions, the permeability of sediments in the horizon-
tal direction tends to be higher than that in the vertical direc-
tion; hence, sediments tend to be anisotropic with respect to
permeability.
- In nature, the presence of small- and large-scale in-
homogeneities in geologic units tends to enhance significantly
the attenuation of contaminant concentrations by dispersion. By
assuming homogeneous conditions in the analysis credit was not
taken for attenuation that would naturally occur. Incorporation
of the factor of heterogeneity in the analysis would, however,
have added considerably to the complexity of the analysis, as
rather involved statistical, stochastic approaches would have
Et?Ec 4—8
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been required. Natural anisotropic conditions result in more
rapid movement in one direction than another, under equivalent
hydraulic gradients. This can be especially important in frac-
tured bedroci where the interconnected fractures may tend to be
oriented in only one direction -- the direction in which flow
will preferentially occur. Consideration of such bedrock aniso-
tropy would also have added considerable complexity to the analy-
sis.
In the analysis, the lowest permeability considered for
sediment layers was 10—6 cm/sec. In nature, sediment materials
may exhibit permeabilities as lo w as i0 cm/sec. Such low-.
permeability materials could have been included in the analysis,
but there is some evidence that flow in such materials may not
take place in exactly the same manner as in higher permeability
sediment. Although sufficient data are not yet available, exis-
ting information indicates that under some conditions Darcy’s law
is not obeyed in such materials; that is, flow rate is not line-
arly proportional to the applied hydraulic gradient. In addi-
tion, the evaluation of the effective porosity and dispersivity
of such materials, both of which are necessary for analysis of
contaminant transport in the subs”rface, is highly uncertain,
given our present understanding of these parameters in low-
permeability clay materials.
The locational settings that were analyzed are rela-
tively simple hydrogeologic settings. Only two saturated layers
were considered, a sediment layer and a bedrock layer, and these
two layers were assursd to have uniform thickness over the entire
flow field analyzed. Thus, the factor of hydrogeologic complexi-
ty was not addressed in this study. Consideration of hydrogeo-
logic complexity would have involved analysis of such conditions
as: a multi-aquifer system; abrupt changes in thickness or
permeability within geologic layers; the presence of faults; or,
tl.e presence of igneous intrusions into sedimentary rocks. Any
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attempt to analyze the effects of such hydrogeologic complexity,
relatively common in nature, would have added greatly to the
effort required for the analysis.
4.2 CONTAMINANT MIGRATION IN THE SELECTED LOCATIONAL SETTINGS
Each locational setting selected for analysis repre-
sents a unique assemblage of locational factors, some of which
are discussed in Section 4.1. The locational factors comprise
both climatic as well as hydrogeologic factors.
Based on the computed arrival time of contaminant
p1uine in the saturated zone at a point located 100 meters down-
gradient of the facility, the settings most likely and those
least likely to limit leachate migration were identified. As
determined by this preliminary analysis, settings most likely to
limit plume migration in the subsurface are those having the
following characteristics:
o Thick, low-permeability unsaturated zone in combina-
tion with a low facility release rate;
o Low-permeability saturated sediment over a higher-
permeability bedrock located in a discharge zone;
o Thick, high-permeability unsaturated and saturated
sediments in combination with a low facility release
rate and a low hydraulic gradient; and,
o Thick, low-permeability saturated sediment in a
recharge zone.
Locational settings that are most likely to promote leachate
migration were found to be those having the following
characteristics:
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o Thin, high-permeability unsaturated zone in combina-
tion with high facility release rate;
o Thin, high-permeability saturated sediment in combi-
nation with a recharge-zone location and absence of
an unsaturated zone; and,
o Thin, high-permeability saturated sediment overlying
moderate to low permeability bedrock in combination
with a thin unsaturated zone.
From consideration of tbe possible combinations of the
locational factors discussed in Section 4.1, it would appear that
the best settings for hazardous waste management would have the
following characteristics:
o Thick, homogeneous, low-permeability unsaturated
zone
o Thick, homogeneous, areally extensive, low-permeabi-
lity saturated zone
o Sediments having good retardation potential
When these characteristics are combined with low facility release
rates, the highest performance of the facility-site combination
can be attained. The worst settings would consist of the oppo-
site set of characteristics combined with high facility release
rates. As can be appreciated, the “best” settings and the
“worst” settings represent only a small fraction of the total
number of settings that exist in the country. The vast majority
of settings exhibit a mix of good and poor characteristics.
Hence, careful site selection and site evaluation becomes parti-
cularly important, so that the good characteristics may be intel-
ligently weighed against the bad characteristics.
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4.3 RELATIONSHIP BETWEEN FACILITY SETTINGS AND LOCATIONAL
SETTINGS
A given facility setting (facility design features and
operating conditions) interacts with the locational setting to
determine the performance of the combined facility-locational
setting. The combination of all facility factors results in a
specific rate and duration of leachate release. Different rates
and durations of leachate release produce different performance
results in a given locational setting. In the presents analysis,
the concentration of contaminants in the leachate was not a
variable. A constant concentration at the source of 1.0 mg/i was
assum d throughout. The results of the analysis, therefore,
represent relative values, rather than absolute ground-water
contaminant concentrations.
The analysis revealed some of the interrelationships
between facility release rates and the characteristics of loca-
tional settings. When release rates are low, the thickness of
the unsaturated zone has a major impact in delaying leachate
migration. Also, when the saturated permeability of this zone is
less than or equal to 10—6 cm/sec 1 very high facility release
rates are required to pass the 1.eachate through the unsaturated
zone in a relatively short period of time. Although not shown
explicitly in the analysis, conceptually it is clear that a low
release rate would imply a greater potential for dilution by
mixing once the contaminant has reached the water table and
begins to migrate downgradient in the ground water.
The number of analyses performed to date have been
insufficient to permit the full evaluation of the relationships
between each facility design factor and the several locational
factors and settings. Of the seven locational settings analyzed
by fate and transport modeling, only two were analyzed using a
wide range of facility settings exhibiting different design fea-
tures. On the basis of these two locational settings, both
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associated with moist-humid climates, some tentative conclusions
may be drawn as to the effect of design factors on specific
performance measures applied to the unsaturated and saturated
zones. For a given climate and facility type, the permeability
of clay liners appears to be the most important design factor, as
discussed in Section 4.1.1. Other important design f ctors in-
clude the failure mode assumed for FilL-lined facilities and the
presence and efficiency of a leachate collection system (See
Section 4.1.1).
In the case of the other five locational settings, it
was npt possible to distinguish among the performance of the few
design cases analyzed. For one humid locational setting invol-
ving a low-permeability sediment layer, and a.facility location
in the discharge zone, leachate from none of the four facility
settings appeared 100 meters downgradient of the facility by the
end of the 200-year simulation period. In this case, the low-
permeability sediment layer and the discharge-zone location com-
bined to mask performance differences resulting from widely dif-
ferent facility designs. Two other locational settings involved
a semi-arid climate and thick unsaturated zones of 149 and
154 feet. In both cases, two landfill designs representing wide-
ly different levels of leachate control, as we]l as one type of
design for a storage surface impoundment were investigated. For
both locational settings, no leachate from the two types of
landfills was computed to have reached the water table within the
200-year simulation period. Hence, the locational setting served
to mask performance differences between the two designs. Due to
the semi-arid climate, both the design representing a low-level
3f leachate control and that representing a high-level of control
produced peak release rates that were relatively low - 2.4 and
1.0 cm/year, respectively, compared to 33.8 and 4.0 cm/year for
the same two designs in a New Orleans-type moist-humid climate.
However, for the case of the storage surface impoundment, because
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its peak release rate was 63.1 cm/year in the semi-arid environ-
ment, significantly higher than I or the landfill designs, travel
time to the water table ranged from 8 to 24 years for the two
locational settings.
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5.0 CONCLUSIONS
The following section provides a summary of the prin-
cipal conclusions reached during the course of the EPA investiga-
tion. The conclusions presented are tentative and represent
conclusions based on the professional judgexnent of the principal
investigators assigned to this project.
5.1 CONCLUSIONS REGARDING CLAY AND SYNTHETIC LINER SYSTEMS
Synthetic Liner Conclusions
Synthetic liner systems can be used effectively to
control leachate migration from hazardous waste management faci-
lities. However, synthetic liners cannot enerally achieve the
current facility containment goals expressed in the Interim Final
Land Disposal regulations. Well designed synthetic liners will
be penetrated by a very limited number of pinholes and installa-
tion holes, and will leak as a result of vapor transport through
the liner systems. Properly installed an tested synthetic
liners will reduce the effective leachate leakage rate below that
obtainable using well designed soil liners. Several significant
problems remain regarding the use of synthetic liner materials in
a hazardous waste environment. The most significant problem
remaining is the projection of the anticipated service life of
synthetic materials. Current experience provides a 10 year data
base for waste disposal applications and a 25 year data base for
other uses. Therefore, synthetic liner service life is currently
based in part on laboratory testing of the rate of change of
liner properties as a result of leachate exposure. Laboratory
test results for specific liner materials in icace a potential
performance life of up to 50 to 150 years. Conservatively,
minimum expected performance life-times of over 25 years are
indicated based on experience with FMLs for various applications,
as well as on available accelerated FML test results.
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Clay Liner Conclusions
Clay liner and cap systems offer a viable means of
controlling most aqueous leachate from hazardous waste racili-
ties. Previous experience with clay as a water barrier material
provides a sufficient data base to allow the construction of
stable barrier layers that can be protected from physic l haz-
ards. Problems exist due to the lack of current testing methods
to assure the attainment of permeability design specifications.
However, the most significant potential problem with clay liners
that remains lies in the current inability to predict the chemi-
cal resistance of clay minerals to certain types of waste leach-
ate, particularly in the long term.
Consideration of Combined FML and Clay Liner
Requirements
The results of the investigation of clay and synthetic
systems indicates that liner system performance could be improved
significantly using double liner systems composed of clay as a
bedding material for synthetic liners. Clay would provide excel-
lent protection and support for the FML and minimize synthetic
liner leakage due to the presence of holes. In addition, the
projected performance of clay liners could reduce the signifi-
cance of the current lack of long term FML performance data.
Quality Assurance Requirement
One of the most important conclusions of the present
project is the need for mandatory quality assurance of liner
installation, operation, and maintenance activities. The inves-
tigation of existing facilities has i’idicated a general lack of
comprehensive quality control of synthetic and clay liner instal-
lation at existing facilities. This problem pervades facility
design, liner installation, and maintenance programs. The tech-
nology required to design and construct an acceptable hazardous
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waste management facility is available. However, the review of
existing facilities indicates a general lack of awareness of the
critical factors involved in the proper installation of liner
systems.
5.2 FACILITY AND LOCATIONAL FACTORS AFFEcTING LEACHATE:MIGRATION
The present analysis has permitted the tentative
identification of those facility and locational factors that are
important in controlling the release and:subsurface migration of
leachate.
The most important facility factors, in order of impor-
tance, appear to be: facility type (landfills, impoundments,
etc.), climate, clay-liner permeability, type of FML failure
mode, and the presence and efficient operation of a leachate
collection system. The major unsaturated-zone factors identified
are thickness of the unsaturated zone (depth to water table) and
the permeability of the unsaturated soil. Although a number of
saturated-zone parameters were determined to be important, those
that exhibited the greatest importance are the permeability and
thickness of the saturated sediment layer and the position of the
facility in the recharge or discharge zone.
Comparison of the performance of seven locational
settings in the model simulations permitted a tentative ranking
of the settings. Those settings most likely to limit the Spread
of contaminants in the subsurface were found to be those having:
o Thick, low-permeability unsaturated zone in combina-
tion with a low facility release rate;
o Low-permeability saturated sediment over a higher-
permeability bedrock located in a discharge zone;
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o Thick 1 high-permeability unsaturated and saturated
sediments in combination with a low facility release
rate and a low hydraulic gradient; and,
o Thick, low-permeability staurated sediment in a
recharge zone.
Locational settings that are most likely to promote leachate
migration were found to be those having:
o Thin, high-permeability unsaturated zone in combina-
tion with high facility release rates;
o Thin, high-permeability saturated sediment in
combination with a recharge-zone location and
absence of an unsaturated zone; and,
o Thin, high-permeability saturated sediment overlying
moderate to low permeability bedrock in combination
with a thin unsaturated zones
From consideration of all the factors, the best com-
bined facility-locational settings would be those which combined
a low release rate with a locational setting involving: a thick,
homogeneous, low-permeability unsaturated zone; a thick, homoge-
neous and extensive low-permeability saturated zone; and, a good
retardation potential. The worst combined facility-locational
settings would consist of the opposite set ot characteristics.
However, the vast majority of the possible sites in tie country
fall in between the two extremes, and, thus, contain a mix of
good and poor characteristics.
The current study revealed some of the relationships
between facility release rates and the performance of specific
locational settings. While the thickness of the unsaturated zone
is always an important factor, it is particularly effective in
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delaying contaminant arrival at the water table when the leachate
release rates are low. Also, when the saturated permeability of
the unsaturated materials is less than or equal to io6 cm/sec,
very high leachate release rates are required in order for the
leachate to traverse the unsaturated zone in a relatively short
period of time. In the case of three locational settings, it was
not possible to distinguish among thc performance of the few
facility designs analyzed. The results showed that in terms of
the appearance of a contaminant plume within the 200-year time
frame, either:
o The combination of a ]ow-perneabi].ity sediment layer
and a discharge-zone location, or
o The combination of a semi-arid climate and a thick
unsaturated zone
can mask potential performance differences among landfill designs
representing widely different levels of leachate control.
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6.0 SIGNIFICANT ISSUES REGARDING LAND DISPOSAL
OF HAZARDOUS WASTES
The EPA land disposal scudy was directed toward the
evaluation and resolution of several technical problems asso-
ciated with the land disposal of hazardous waste. Based on the
results of this investigation an approach was developed to re-
solve many of the problems which have occurred at existing waste
disposal facilities. In addition, the study served to focus
attention on remaining problems and the need for further re-
search.: The following section provides a qualitative discussion
of the significant issues that must be addressed, in order to
implefflent the recommendations of this study. These issues may be
classified as institutional issues because they require the corn-
mitmént of personnel and financial resources. Basically, the
required technical approach has been defined. It remains to be
determined how this technical approach can be implemented in the
short and long term.
6.1 QUALITY ASSURANCE - HOW MUCH IS ENOUGH
One of the principal recommendations of this investiga-
tion is that construction be completed under mandatory quality
assurance (QA) control. The degree of QA required is propor-
tional to the risk of facility failure and the severity of the
consequences of facility failure. The results of the current
study clearly indicate that questions remain regarding the impor-
tanceof locational factors, long term facility performance pro-
jections, and chemical resistance testing. Further, the current
study served to demonstrate the complexity associated with proper
facility design, construction, operation, and maintenance. Given
these concerns, a relatively comprehensive QA program will be
required to insure that all aspects of facility development are
adequately addressed and to provide thorough documentation of
facility development in the event that failure occurs and repairs
must be performed.
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The question remains as to how QA can best be imple-
inented. Several alternatives exist. The program could be imple-
mented similarly to that imposed by the EPA in other areas such
as air quality programs or other EPA, DOE, and NRC programs.
Regardless of the approach selected EPA must commit sufficient
financial and personnel resources to evaluate QA compliance and
facility designs. The availability of adequately trained and
experienced personnel to conduct these evaluations must also be
considered. The QA approach may be structured to provide third
party r view in an attempt to fill the experience gap or EPA
could endeavor to train and commit the necessary personnel either
internally or using consultants.
6.2 CONSERVATIVE FACILITY DESIGN
The various investigations completed indicate that more
conservative designs reduce the risk of facility failure and
leakage. The question remains as to how conservative a des±gn
must be, based on the uncertainties concerning liner integrity
and locational complexity which remain. Certainly, more conser-
vative designs should be considered for the disposal of particu-
larly hazardous materials or to protect particularly sensitive
environmental areas. But to what extent should conservative
designs such as double liners, synthetic over clay, etc., of
normal facilities be required? The question must ultimately be
answere4 by EPA in the public forum.
The rationale used in developing recommendations from
this study represents what we believe is an acceptable approach
that recognizes the practical need for adequate waste disposal
capacity and the need to protect human health and the environ-
ment. The approach recommended would require comprehensive QA of
combined clay and synthetic liners for normal facilities. The
liner design would be reinforced by a requirement for leachate
and liner decay monitoring. The monitoring systems would provide
an early warning system to indicate liner decay and unacceptable
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leachate buildup within the unit. The early warning system is
required, due to the uncertainties that remain regarding liner
chemical resistance and long term performance. With the moni-
toring system in place, potential failure of the unit would be
indicated before environmental contamination occurred. This
would allow sufficient tine to accomplish repair of the unit or
the removal of the waste material prior to widespread contamina-
tion. Essentially, the approach proposed would utilize “sf te of
the art” facility designs backed up by monitoring systems de-.
signed to indicate potential failure before environmental con-
tamination occurs. Less conservative single liner containment
systems could be used at specific locations that exhibit hydro-
geologic conditions favorable for waste containment. Specifica-
tion of the particular conditions required to support single
liner designs will require additional research. Similarly, waste
disposal at facilities located in undesirable hydrogeologic set-
tit&gs either should be banned entirely, or should be required to
utilize more conservative facility designs to insure adequate
protection for the area.
6.3 FACILITY DESIGNS AND LOCATIONAL FACTORS FOR PARTICULARLY
HAZARDOUS MATERIALS
Particularly hazardous or mobile wastes pose special
problems for hazardous waste disposal. Liner studies have indi-
cated tha several classes of materials such as strong solvents
and concentrated acids may degrade some liner materials. Fur-
ther, some waste components are highly mobile within the ground-
water system and other wastes pose unacceptable risk due to their
extreme toxicity to humans or the environment. These wastes and
waste components must be treated as special wastes which require
extra design precautions.
The approach to classifying waste materials is accor-
ding to the degree of risk they pose to the environment. Such a
classification system is not presently ’ available and will require
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further research to develop. The State of California has imple-
mented an approach based on waste treatability. However, such an
approach does not address the question of environmental risk. A
more suitable classification that recognizes risk and treatabi-
lity is recommended.
Similarly, variations in the risk imposed by specific.
locational settings must also be considered. Some hydrogeologic
systems provide avenues for rapid contaminant dispersal through
the groundwater system. Other settings are so complex that
current analysis techniques cannot be used to assess the conse-
quences of a waste management facility failure on the area.
Thes unusual locational settings increase the risk associated
with the operation of a hazardous waste management facility.
Simpler locational settings and settings that provide a signi-
ficant level of natural containment would reduce the risk asso-
ciated with waste management facility operations. The risks
associated with the selected facility location and the types of
wastes to be handled must be considered in the design, operation,
and maintenance of hazardous waste management facilities. A
similarly developed classification system to that discussed above
for specific waste components is also needed for facility loca-
tion classification to account for varying degrees of risk asso-
ciated with hydrogeologic site conditions.
Once a suitable classification system is developed it
will be necessary to define degrees of conservatism in facility
designs needed to handle these special waste materials and speci-
fic site locations. The approach recommended would establish a
graduated system of design or performance specifications depen-
ding on the classification of the waste material to be handled
and the hydrogeologic conditions et the selected site. The range
of standards would start with basic enhancements of the recomrnen-
ded FML and clay liner design and continue through multiple liner
systems with leak detection capability, etc. The most conserva-
tive designs may not be sufficient to handle all wastes, or al]
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locations. Some wastes may not be suitable for land disposal
regardless of design. Similarly some sites may not be suitable
for any hazardous waste disposal activity.
6.4 EPA RESOURCE AND MANPOWER COMMITMENT
The hazardous waste disposal problem can be handled
effectively using available design, construction, and maintenance
procedures. However, the long-term nature of waste disposal will
require an irreversible commitment of personnel and financial
resources. Resource commitments are needed to ensure adequate
facility records management, facility inspection, and emergency
or remedial action design and response capability. The necessary
personnel resources can be provided from internal EPA staff,con-
sultants, or other third party organizations. The most important
point is that the commitment to the safe disposal of hazardous
waste must be continuous and uniform. The commitment of re-
sources must be maintained over the long-term and not allowed to
diminish over the coming years if problems do not occur imme-
diately. This represents a critical institutional problem, since
without proper commitment of resources, hazardous waste manage-
ment facilities will surely fail either in the short or the long
term.
6.5 SITE SPECIFIC DESIGN CONSIDERATIONS
The location-factor analysis conducted during the
course of this program represents a first approach toward asses-
sing the importance of the facility locational setting to t e
overall design process. As the first approach, the study results
serve more to identify the scope and complexity of the issue than
to resolve this prob1er . The results obtained indicate that the
regional setting is important to the determination of the amount
of facility leakage generated and the dilution potential of the
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site area. It remains to determine how this information can be
used to establish a practical approach toward incorporating site-
specific considerations within the RCRA regulatory framework.
The central issue is the d&velopment of a comprehensive
classification system to establish design or performance specifi-
cations by area or region that will be bquitable. The regulatory
approach for implementing such a system is reasonably well estab-
lished in other EPA regulations such as the Prevention of Signi-
ficant Deterioration program in the Air Quality Program and
similar classification programs in the Water Quality Program.
However, the complexity of hydrogeologic systems within the same
region of the country often varies from one extreme to the other.
Based on the initial results obtained, it appears that complex
hydrogeologic areas pose a greater threat, should failure occur,
because the ultimate fate of the leaked contaminants cannot be
determined. Simpler locational settings allow the monitoring
of contaminated ground water plumes, which would presumably allow
eventual clean up of the contaminated aquifer. Using this per-
spective it would appear that more complex locational settings
would require a more conservative facility design approach than a
simpler system in order to provide similar safety margins for
both facilities. Alternatively, precipitation as the principal
hydraulic driving mechanism could also be considered as an impor-
tant regional classification indicator.
Such a classification system could be developed to
adequately address the primary technical issues, but fail to
recognize other factors that are important in the context of
hazardous waste disposal. For example, each State is responsible
for the disposal of all low-level nuclear waste generated within
the State under current regulations. Hazardous waste represents
a similarly sensitive issue. Should the EPA elect to require
that all waste generated within a specific region be disposed of
in the same region? And, .f uo, is it equitable to require more
conservative and expensive facility designs for some regions than
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for others? These questions must be addressed i light of the
apparent importance of locational factors to waste management
facility performance. This study served primarily to identify
the significance of hydrogeologic factors. Further investigation
of the technical aspects of facility siting standards and the
evaluation of institutional factors is needed before an equitable
regulatory approach can be developed.
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7.0 RECOMMENDATIONS
The following provides a concise summary of the recom-
mendations that resulted from the EPA Liner and Locational Factor
Analysis project. The recommendations provided were developed o
improve hazardous waste management facility performance by ob-
taining ai itional information regarding the design, installa-
tion, operation, and maintenance of these facilities. Recommen-
dations are provided in three areas: regulatory reform, techni-
cal guidance requirements, and areas requiring further research.
These recommendations are based .primarily on the professional
judgement of hazardous waste experts involved in this project.
7.1 REGULATORY
The results of the investigation performed indicate
that some regulatory re-evaluation may be warranted. The princi-
pal. regulatory amendments recommended include the use of a double
liner, composed of an FML and a clay liner, at disposal facili-
ties; modification of the allowable leachate level above FMLs;
and the incorporation of formal quality assurance requirements.
Other recommendations provided in lude several minor changes that
could be accomplished directly on the basis of available techni-
cal information, such as clarification of the allowable “de
minimus” liner leakage rate and quantification of the terms
“short-term” and “long-term” performance goals. Several addi-
tional recommendations are provided that will require the comple-
tion of additional research prior to implementation. P.. ssible
changes in the arf.a of locational standards are provided, but
will require further research prior to implementation.
Any approach to the incorporation of location standards
in regulations governing hazardous-waste sites must establish the
goal of integrating facility design and operation .vith the loca-
tional setting. From the perspective of this study, locational
factors and site acceptability are of greater importance for
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disposal facilities than design and operation considerations.
However, once a site has been deemed acceptable, then the level
of environmental protection provided by the site and vicinity
will be based on the selection of facility design and operating
procedures suitable for the particular site and the expected
waste stream.
o The objective of containing all leachate emanating
from hazardous waste management facilities during
the active life of the facility should be reviewed
to determine what “de minirnus” leakage level would
be acceptable. The level of leakage allowed under
the “de xninimus” concept should be set to the mini-
mum leakage expected from well designed and con-
structed FMLs as well as for clay systems, indepen-
dently.
o A formal quality assurance program covering all
aspects of facility design, installation, operation
and maintenance should be required as part of the
permit process.
o Standard chemical resistance testing procedures and
criteria must be required for both synthetic and
clay materials. “Compatibility” must be defined.
o The requirement to limit leachate rise above the
liner to 30 cm should be modified to allow somewhat
higher leachate head levels for synthetic systems so
that greater protection of the leachate collection
and FML system can be provided. This would result in
minimal leakage increase because FML leak r .tes are
not primarily dependent on hydrostatic pressure.
Should combination liners be required, an increase
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in the allowable leachate level would allow the
installation of a clay bedding liner above the FML.
The 30 cm allowable leachate level should not be
modified for clay-only systems.
o Removable coupons of the FML material used at a
particular facility should be required to be placed
in the leachate collection system to enable
verification of chemical resistance testing and
determination of continued FML integrity during
and following operation.
o Leachate levels should be monitored within the waste
management facility during operation and after
closure.
o EPA should consider requiring a double liner system
composed of a clay liner and an FML. The combined
properties of these two materials would signifi-
cantly improve the anticipated performance of cap
and liner systems at many hazardous waste management
facilities.
o The closure period should be extended to allow the
installation of temporary caps in order to allow the
rate of waste subsidence to stabilize prior to in-
stallation of the permanent cap. Leachate collec-
tion must continue during this interim period..
o A hydrogeologic assessment of the facility area is
needed prior to permitting in order to provide the
necessary information to assess the fate and trans-
port of ]eachate that might escape the facility.
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o It is envisaged that two types of locational stan-
dards may be adopted. The first type would involve
those standards for identifying clearly unacceptable
sites. These standards may be viewed as “rejectir j
standards”. The second type of locational standards
would aim to “pair up” each acceptable site with the
facility design/operation scheme most a propria e
for the climatic, hydrogeologic and waste-stream
conditions.
7.2 GUIDANCE MATERIALS
The results of the liner and locational factor study
indicate that further technical guidance would prove beneficial
in several areas to alleviate misconceptions and mprove facility
performance. Recommendations regarding the preparation of addi-
tional. guidance material are provided in the areas, of: quality
assurance of hazardous waste management facilities, the specifi-
cation of standard permeability and chemical resistance testing
procedures, and in the identification of specifiG hydrogeologic
factors of significance to facility design.
o Guidance material should be developed to standardize
chemical resistance testing of both clay and synthe-
tic liner materials. Standardization of testing
protocols, sample preparation, and representative
leachate is required, along with the development of
specific liner material acceptance criteria for both
types of liner materials.
o Technical guidance should be deve. oped regarding the
acceptability of various hydrnlogical models, and
their appropriate use in the permitting process.
o Technical guidance specifying the minimum require-
ments of an adequate hydrogeologic site investiga-
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tion is required. The investigation should include
areal density of borings, depth of borings, type and
level of information required from each boring, and
the nature and number of field and laboratory tests
required.
o A comprehensive quality assurance pr gram should be
developed to support the permitting of hazardous
waste management facilities. The program may be
designed using other formal EPA: quality assurance
programs as guidelines.
o For FilLs, additional guidance is required to stan-
dardize the use of current liner property testing
methods in projecting ultimate liner serviceability.
o Following the necessary research, guidance speci-
fying the acceptable equipment and procedures for
both field and laboratory testing of clay liner
materials, as well as a means to correlate the two
types of tests should be developed.
7.3 RESEARCH RECOMMENDATIONS
The results of the liner and locational investigation
indicates a strong need’ for further research regarding the per-
formance and durability of clay and synthetic liners in the
presence of hazardous waste leachate. The study also indicates a
need for significant further research in facility design mo ’eling
and in the specification and importance of locational factors to
facility design. One of the principal objectives of this inves-
tigation was the ic entification of areas that are not presently
understood and require further investigation. The following
provides a summary of the principal areas that should be investi-
gated in support of future regulations and guidance.
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o Further research is needed to develop appropriate
testing methods to verify the attainment of design
specifications of manufactured liner materials.
o A central data base of chemical resistance testing
results should be established for both clay and
synthetic materials.
o Scientific cause-and-effect investigations and docu-
mentation of liner failure at well-designed faci-
lities should be conducted. Successful facilities
should also be thoroughly investigated.
o Further research is required to improve the standar-
dization of chemical resistance testing procedures
to allow direct comparison of results between tests.
Research is needed both for FMLs and clay liners.
o An investigation of synthetic and clay liner proper-
ties is warranted to determine specific criteria for
liner chemical resistance determinations.
o Further investigation of the vapor transport mecha-
nism within synthetic materials should be conducted
to determine its significance for specific leachate
types and particular synthetic liner materials.
o Testing methods should be developed to allow liner
resistance monitoring at hazardous waste management
facilities during and after the operational phase of
the fac.ility.
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o A research effort should be conducted to examine the
stability of a conservatively designed waste manage-
ment facility in the presence of upward hydrostatic
forces. Such conditions could result in uplifting
and associated liner failure.
o Further in .stigation of the design,. construction,
and long-term performance of refined clay materials
for hazardous waste containment should be conducted.
Refined clays offer more homogeneous materials that
can be chemically tested more reliably than unre-
fined clay soils.
o Improved quality control tests for liners should be
developed and better correlation between test re-
suits and actual performance should be pursued.
o Development of more reliable techniques for detec-
ting subtle discontinuities in in-situ clays to
ensure their removal.
o Investigation of improved techniques and equipment
for uniformly distributing water in clay to develop
optimal moisture content.
o Development of improved methods of determining per-
meability both by field tests and by laboratory
tests for clay materials and installed liners.
o Assessment of the effect of dessication cracks on
the rate of infiltration through caps.
o Investigation of the thickness and characteristics
of bedding soil layers needed to protect FMLs.
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o Chemical compatibility testing of solvents with clay
liners in single phase solutions comprised of mixed
organics in varying proportions with water is
needed.
o Polymer treated bentonite should be tested for long-
term chemical resistance.
o Further sensitivity testing of the HELP model is
required in order to estimate overall model accuracy
and reliability. Field verification of the model
may be warranted following the additional sensi-
tivity testing. Modification of the code is also
recommended so that the present assumption of free
drainage through the bottom liner is changed to
permit assignment of a range of possible soil pore
pressures beneath the liner.
o A complete evaluation of the system of hydrologic
models used to support this study is required in
order to improve the compatability and accuracy of
the various models uscd in subsequent assessments.
Consideration should also be given to the use of an
alternate integrated unsaturated-saturated hydro-
logic model for future analyses.
o Further investigation of other locational settings
is needed to provide information concerning the
sensiti’ ity of facility performance to minor changes
in locational settings.
o The investigation of various complex locational
settings, which are frequently encountered in the
field, should be conducted.
EEtE,e 7-8
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o An investigation of various methods to estimate
regional recharge rates that are more consistent
with facility leak rates is required to support
subsequent modeling efforts.
o An investigation of the possible mounding effects
that may occur at the saturated and unsaturated zone
boundary is required.
o A detailed evaluation of the decay mechanisms that
affect hazardous waste components is needed to
assess the effective .decay rate of these materials.
EEitec
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APPENDIX
PUBLIC COMMENTS AND EPA RESPONSES:
LINER/LOCATIONAL ANALYSIS PROJECT
I. COMPREHENSIVE ISSUES
II. CLAY LINER AND CAP ISSUES
(1) Genera].
L2) Liner/Waste Compatibility
III. SYNTHETIC LINER AND CAP ISSUES
(1) General
(2) Design and Installation
(3) Leachate Release and Facility Failure
IV. LOCATIONAL ISSUES
(1) Regulatory Requirements
(2) Hydrogeologic Settings
( .3) Design/Location Interrelationships
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I. COMPREHENSIVE ISSUES
Q—l. Is the use of a clay and synthetic combination liner system
a feasible alternative to current liner requirements?
A. Installing a synthetic liner over a clay liner provides the
optimum level of protection against facility failure and
eventual leachate migration. The short—term containment
capabilities of a synthetic liner would be complimented L
the long—term buffering capabilities of a clay liner.
Recommendations have been made to EPA to consider requiring
a combination clay and synthetic system for l ners in land
disposal facilities. (Reference 06. Section 4.0.)
0—2. Should EPA evaluate the effectiveness of requiring a back—up
clay liner under an FML when there is a potential for adverse
gçound—water impact?
A. Based on the results of the HELP modeling analysis, the
construction of flexible membrane liners (FML) over clay
liners offers a significant reduction in facility seepage.
The addition of the clay significantly reduces the seepage
over a single FML that developed holes for landfills, surface
impoundments, and waste piles. The most significant
improvement was for surface impoundments. (Reference #2,
Appendix G and Reference 06. Section 3.8.)
0—3. Should the use of a double liner be cause for exemption from
the ground—water monitoring requirements of Subpart F?
A. This question was not specifically addressed in the study.
Q—4. Provide available information on the following technical
aspects of clay and synthetic liners:
A. Special handling and placement procedures
B. Sensitivity of seaming (FMLs only)
C. Care required for placement
D. Monitoring and testing
E. Operational protection to prevent puncture
F. Q emical resistance analyses
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A. References to the above topics are as follows
A. Reference #3, Section 4.0. Reference i, Section 4.0
B. Reference #4, Section 4.0
C. Reference #3, Section 4.0; Reference #4, Section 4.0
D. Reference #3, Section 3.0 ; Reference #4, Section 3.0
E. Reference #3, Section 5.0; Reference #4, Section 5.0
F, Reference #3, Section 3.0; Reference #4, Section 3.0
Q—5. Should the Agency set performance standards for liners and
caps based on the type of waste, flow rate through the cap or
liner, or some other criteria?
A. The current approach using a general performance standard
appears appropriate for most waste types. However, facility
design standards or modified performance standards may be
‘required for facilities accepting particularly hazardous or
mobile waste components, or for facilities that are located
in particularly sensitive environmental settings.
Recommendations have been made to EPA to identify sensitive
settings and to provide appropriate design and operating
requirements. (Reference #6, Sections 7.0 and 8.0.)
Q—6. How does the regulated community define a liner?
— synthetic only?
— synthetic and recompacted clay?
— synthetic and recompacted clay and in—situ clay?
— synthetic or “natural” clay?
A. Although not specifically addressed in this project,
interview results indicate that synthetic materials, recompacted
clays, and in—situ soil materials are defined as functional
liners by hazardous waste facility owners or operators.
(Reference #10, Volume I, Section 4.0.)
Q—7. Can and should liners be designed and engineered for specific
site conditions?
A. Liners and other designed :components of a hazardous waste
facility should be engineered appropriately for the specific
site conditions. Recommendations have been made that EPA
establish locational standards in the Part 264 permitting
requirements. The goal of the final Part 264 standards
would be to design and operate a facility in a manner that
was appropr’ate for the specific site conditions. (Reference
#5, Section 5.0.)
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Q—8. Should Ek A require that a hazardous waste facility be
constructed with a synthetic or a clay liner, on a site—by—
site basis?
A. The locational analysis conducted during this investigation
indicates that liner requirements should be integrated
with the hydrogeologic setting. Recommendation to amend the
current Part 264 permitting standards to reflect this goal have
been made. (Reference #5, Section 5.0.)
Q—9. What is the “intragradient” landfill design concept? What
is the optimum level of leachate head inside the liner
(assuming comrnenter is correct arid a one—foot head requirement
is not appropriate)? Should there be a general restriction
on land disposal below the seasonal high water table? Does
the intragradient design concept include clays and synthetics?
A. The “intragradient” design concept is emplacement of wastes
into in—place, satur ted soils of low permeability. Th term
“intragradient” is better defined as “below the water table.”
Unlined land disposal facilities that terminate in saturated,
low-permeable soils may provide equivalent or greater levels
of leachate containment than lined facilities terminating in
unsaturated, low—permeable soils during the active life of
the facility. Under saturated soil conditions, generally
smaller volumes and masses of leachate will, move across facility
boundaries. No optimum head can be defined under these conditions
since all hydrogeological settings will be different. However,
lower heads must be maintained for facilities in saturated
environments.
The “intragradient” design concept relies upon in—place,
natural soils of low permeability to provide containment
equivalent to an impermeable liner. However, there are no
cover or leachate collection system designs that are now
required by EPA, that are designed specifically with the
intragrãdient design concept. (Reference *12, Appendix C.)
Q—l0. Should monitoring (QA/QC) the installation (installed
performance) be undertaken regardless of liner type?
A. Implementation of formal quality assurance/quality control
requirements is r cornmended for the construction and operations
of all types of hazardous waste management facilities.
(Reference #10, pp. 3—1, 3—17 to 3—20, 7—1 to 7.6.)
0—11. Can plastic drainage materials such as Netlon substitute for;
— leachate collection system?
— leakage detection system?
— drainage layers?
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A. This item has not been addressed in the EPA studies undertaken
recently. In yeneral, specification and substitution of
leachate collecti , detection and drainage materials has
not been discussed. It should be noted that all analyses of
liners and other components of facilities is usually done by
class of material, such that plastics are divided into
categories of unvulcanized plastics, plastics with high
crystalline struc; - ure, and thermoplastic elastomers. Specific
brand names are not mentioned.
Q—12. Should disposal facilities not operate until the liner
construction and installation has been examined by a qualified
professional? Would third party certification (by an
independent professional) further serve to ensure that the
liner has been properly installed?
A. ‘Disposal facilities should not be allowed to operate without
verification of proper liner installation. Verification
could be provided through the use of a formal quality
assurance program, which would be verified and audited by EPA
personnel. A third party arrangement could also be used to
verify proper installation, but a quality assurance program
would still be required. A comprehensive QA program would
ensure that all aspects of facility development are fully
documented. This would prove invaluable should problems
develop at the facility and remedial action be required.
(References #9, p 7—56 and #10, p 3—33.)
Q—13. Can EPA document cases where properly installed soil or
synthetic liners •have resulted in significant contamination
of ground water?
A. The studies did not document specific cases where liners
have failed. However, the studies did consider factors
affecting liner performance and liner failure modes. Many
different factors can impact the performance of a liner
ranging from raw-material preparation, manufacturing,
fabrication, transportation, design, site preparation, and
field installation. The hierarchy of failure modes considered
include: (1) philosophical/conceptual; (2) process; (3)
categorical, (4) prelimina y failure; and (5) ultimate
failure. (Reference #10, pp. 3—3 to 3—31 and *7, Section 4.)
Q—14. Evaluate a study by Peter Montague, entitled. “Four Secure
Landfills in New 3ersey...A Study of the State of the Art in
Shallow Burial Waste Disposal Technology.”
A. EPA has begun such an evaluation of this report by Peter
Montague. The results of that evaluation were not available as
of the date of this report. EPA will issue the results as a
separate report.
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Q—15. Are any studies available regarding bacterial deterioration
of liner material components, plasticizers, or other
addiLa.ves? Is such deterioration significant? If so, how
significant.
A. Biodegradation of synthetic liner material should be a very
slow process, since most synthetic polymers are attacked at
the chain ends that are hidden in the polymeric matrix and
almost inaccessible to enzymes. There are few microorganisms
prepared to attack synthetic plastics, although many are capable
of the necessary adaptations. For most synthetic polymers
the biodegradation process should take hundreds of years.
There is evidence that for the low molecular weight
constituents, such as plasticizers or other additives, the
process may be significant. (Reference #7, pp. 4—18, 4—34,
and 4—39 to 4—43.)
Q—l6. Does the placement of bulk liquids in landfills increase the
potential for chemical resistance failure in clay and/or
synthetic liners?
A. This question was not specifically addressed by this study.
Q—17. Is it useful to compile data on effects of each Appendix VIII
constituent on each type of liner?
A. Development of a data base that compiles information on the
effects of listed hazardous wastes with various liners is an
important step in understanding waste—liner interactions,
in predicting performance of facilities, and in designing
a comprehensive waste management system. The collection
of data on the interaction of a specific waste with a
specific liner could lead to the development of a
classification system that would be used in restricting or
allowing certain wastes in certain facilities. It must be
recognized, however, that three significant problems
exist: the extremely complex structure of. clay minerals
and the equally complex characteristics of waste streams
make theoretical assessment infeasible; standardization of
testing procedures is required in order to compare laboratory
results; and results of field performance are extremely
difficult to obtain. (Reference #6.)
Q—18. How confident are we in state—of—the—art vadose zone
monitoring techniques for use with land disposal facilities
other than land treatment sites?
A. This question was not specifically addressed by the study.
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Q—19. Should there be a maximum operating life on storage surface
impoundments after which they would have to comply with the sarnc
requirements as disposal surface impoundments.
A. This study did not address this question.
Q—20. Should EPA provide a variance from the design ].eachate level
standard (one foot head) for landfill designs that demonstrate
that leachate level control is not a major concern?
A. This question was not.specifically addressed by this study.
Q—21. Should EPA specify the point on a liner at which leachate
depth should be measured.
A. This question was not specifically addressed by this study.
Q—22. Should EPA consider either increasing or decreasing the
maximum leachate depth of 30 cm during both the active life
of a landfill and the closure period?
A. I t is recommended that EPA allow a maximum leachate depth
of greater than 30 cm for FMLs only, to allow a thicker
protective layer for the liner and leachate collection system.
(Reference *4, Section 8.3.1.4.)
Q—23. Is it possible to construct a liner that is completely
impermeable for containing hazardous wastes for 10 years or
more? What is the range of expected working lives for
various synthetic liner materials?
A. It is not possible to construct a liner that is totally
impermeable. All clay liners have some finite permeability.
All synthetic liner materials allow some seepage due to the
vapor transport phenomenon, in which volatile materials
(including water) may permeate through the material in
response to a concentration gradient. However, it is
possible to install a synthetic liner which will only allow
minimal seepage (due to vapor transport) for greater than
10 years, provided that it is resistant to chemical waste
products and that it is installed properly. (Response #4,
Section 3.0 and 5.0.)
Q—24. Should EPA have a peer-review group or SAB review of
technical decisions regarding liner re juirements that may
be based upon the results of the liner/location analysis
and current research and literature?
A. This question was not specifically addressed.
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II. CLAY LINER AND CAP ISSUES
C].) General — Questions 1—8
Q—l. Under what specific circumstances do clay liners provide a
higher degree of protection than synthetic liners?
A. Clay liners provide a higher degree of protection than
synthetic liners in the following ways: (1) Clays experience
less irreversible changes in permeability when exposed to
incompatible waste materials than do synthetics, and, (2)
Instállation techniques for clays allow more confidence in
the long—term liner integrity. (Reference #6, Section 3.)
Q—2. Mow much do we know about performance of bentonite clays?
Any experience under actual field conditions of bentonite
mixture with soils and its ability to provide a “sealer”?
How about the American Colloid treatment process for
bentonite? Is EPA aware of this?
A. This study did not specifically assess the performance of
installed liners constructed with bentonite clays.
Q—3. How good is our ability to measure permeability of clay
liners, once installed in the field? Is there a significant
discrepancy between laboratory measurements and actual
field conditions? Also, what effect on clay liner permeability
is a result of saturated versus unsaturated conditions?
A. Field permeability test methods to measure installed
permeability are not standardized. The ability of field
procedures to measure clay liner permeability remains
unresolved. A comparison of corresponding laboratory and
field hydraulic conductivity test results shows the field-
measured hydraulic conductivity to be unpredictably higher
than values measured in,the laboratory. Compaction of
clay dry or wet o.f optimum can greatly influence the
permeability so quality assurance/quality control procedures
during construction are imperative. (Reference *9, pages
2—1 to 2—23.).
Q—4. DC. natural liners reseal themselves or can they be effectively
repaired in place?
The shrink/swell behavior of kaolnite and il.lite differs
from that of montmorillonite. These clays shrink upon
dehydration, but show very little swelling upon subsequent
rewetting. This characteristic limits the capacity for
these two clays to self heal or to close shrinkage cracks
once they are formed.
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1unt. i r ii .Lon i t clay ‘_‘xh )its orn’: i’ I —IIL 1 Ii ‘j •‘ Le
r m cracks caused by Ic wat.2r11•J, but i ,oth L - Li nJ
labor. tory oL s rvat ions ir iic t. thdt ta.. . ALIJr• ‘ .. ‘ Wt
be entirely corrected by rewetting. Other complicating
problems associated with chemical incompatibility ma ’ make
the self—healing mechanisms ineffective.
Repairing dessication cracks in clay soil requires the sarae
procedures as installing a new liner. Clay soil contaminbted
with hazardous wastes may not be recompactable. (Reference *9,
6—34 to 6—37.)
Q—5. Mow effectively do soil—based liners treat leacliate, thereby
reducing the contamination potential of hazardous constituents?
A. This question was not specifically addressed by tnis study.
1 There is a brief overview in reference 9 page 6—115. The
study does recommend that this characteristic of clay
be further investigated to take advantage of this property.
A considerable amount of research has already been done on
the subject of attenuation in clay soils. This area may be
particularly pertinent for metal wastes in storage surface
impoundments and monofills. (Reference *9, pp 6—115.)
Q—6. Should a clay liner be used as a media to treat leachate in
order to prevent migration during the operating life of the
facility?
A. This question was not specifically addressed by this study.
Q—7. Should soil cement be considered a liner material in
combination with a synthetic material?
A. This question was not specifically addressed by this study.
Q—O. Can soil cement significantly improve the FML liner performance?
A. This question ias not s [ ecifIcally addressed by this tuJy.
(2) Liner/Uastes Compatibility Issues — Questions 1—3
Q—l. Do clay liners become more impermeable when exposed to
wastuwater with high sodium content? Is there any Jata to
support thi5? If so, what are the im Lic3tLon i•r . lay
liners?
A. The .ffeet u u wast bJat r witi high sodium eunt :it th•
j t rmealL1ity o a cL iy li: r ic nds h i hly )fl th. ) Ci IC
physical propeLtius of the cidy it thu stt . Iost L y
minerals have sheets oE layered structures, cni the ptesencc
of water b twucn thesu Layers dfl determine the basic
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physical properties of the clay. The swelling of clays
causes a decrease in porosity, and thus, a decrease in
permeability. Swelling is usually greater in soils with
clay particles of greater surface area, such as found in
montmorillonite. The absorption of both polar and non-polar
molecules can significantly afI ect the spacing between
clay layers. Monovalent exchangeable cations, such as
sodium, generally cause greater swelling thar, divalent
calcium ions.
The swelling of montmorillonite clay with its exchangeable
sodium, would appear to make it an attractive candidate for
liner material. However, the swelling can be reversed by
changes in salt content of the permeant or by certain
organic fluids, resulting in increased permeability. Also,
if excess sodium ions are present in the water available
‘to saturate the clay, the result may be a decrease in
interlayer spacing due to the competition of the ions with
the clay surfaces for the free water molecules. This
interference with swelling would increase the permeability
of the clay. (Reference #3, Section 6 and 7, Reference #9,
Section 2, 4, 6.)
Q—2. If certain organic solvents can destroy the integrity of a
clay liner system, is there a solvent to solute (water)
ratio below which the water “protects” the integrity of
the clay liner and prevents breakdown by the solvent?
A. Although a detailed review of the literature on the effects
of organic solvents on clay liner systems was conducted, no
information was obtained on the existence of a solvent to
solute ratio which prevents permeability increase in clay
liners. (Reference #9, Section 6.)
Q—3. Are there certain types of wastes which, when disposed in a
clay—lined facility, will enhance the containment properties
of the liner through chemical/physical interaction? If so,
is it reasonable to allow a variance to the FML requirement
for facilities that are permitted to accept only wastes
that will enhance the liner’s containment properties?
These questions were not specifically addressed by thi. study.
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III, SYNTHETIC LINER AND CAP ISSUES
(1) General — Questions 1—3
Q—1. Voiclay is processed bentonite? Should it be included as a
synthetic liner material?
— Is this material self he .ling from root penetration?
— Is water flow through this material different from natural
clays?
— Can bentonite be .used as a substitute to synthetic liners on
a site specific and/or waste specific basis?
— Are bentonite and native clays substantially different
liner materials?
— How do they differ for the following?
a. cation exchange capacity
b. specific surface area of bentonite
c. specific expansibility
d. particle size distribution
e. plastic limits
f. self—healing properties (are these specific to certain
classes/types of waste)
g. permeability
h. chemical resistance/biological degradation
i. cracking
j. subsidence/differential settlement
k. installation procedures (uniformity of material)
1. attenuation and adsorption
In. waste compatibility/incompatibility
A. The information on these issues is given in Reference #9,
pages 2—4, 4—24, 4—25,and Reference #10 pages 6—1 to 6—4.
Q—2. What are the advantages and disadvantages of a synthetic
liner system over a clay liner system?
A. Flexible membrane liners offer the following advantages:
o prevent seepage
o provide a uniform material
o material properties can be changed for different waste
characteristics
and disadvantages:
o have a finite lifetime which is unknown at the present time.
(Reference *7, pages 1—3 to 6 and Section 6.)
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Q—3. Is adulteration of synthetic liner materials a concern? Is
Hypalon really 100% Hypalon? If not, what is it and what
difference does it make?
A. This question was not specifically addressed by this study.
(2) Design and Installation — Questions 1—7
Q—l. Since synthetic liners do fail, should EPA require a back—up
natural clay liner with a complete leachate collection
System?
A. The results of the HELP modeling analysis showed that a FML
over a clay liner reduces the seepage from a single FML after
failure of the FML. All flexible membrane liners must be
considered as having a finite lifetime depending on the servic
conditions. There is no basis for believing that they will
always remain serviceable, but under proper design and operating
conditions, FMLs may last for considerable lengths of time. A
recommendation has been made that EPA consider requiring a FML
over clay liner system for all new facilities. (Reference #7,
page 6—1, and Reference #6, Section 3.)
Q—2. Are synthetic liners appropriate for use in locations where
the water table fluctuates causing a varying hydrostatic
pressure around surface impoundments?
A. Synthetic liners can be installed in ground-water discharge
areas where varying hydrostatic pressures may be exerted on
the liner. This aspect of design and installation was not
addressed in this project. However, the interview results
do not contain any reference to hydrostatic pressure as a
significant problem. Recommendations have been made to EPA
to study the effects of upward hydrostatic pressures on the
long—term integrity of synthetic liners. (Reference #4,
Section 1.0.)
Q—3. What are the technical problems associated with storage and
handling of synthetic materials? —installation of synthetic
liners and caps? —testing and monitoring of installed
synthetic liners and caps? How significant are these problems?
A. The present analysis has included a detailed investigation
of the following technical areas related to synthetic liners:
a) Chemical and Physical Properties;
b) Installation and Material Storage and Handling;
C) Expected Service Life of Synthetic Materials;
d) Failure Modes;
e) Performance Modeling.
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It was concluded that installation, storaye, and handliny
problems can be adequately resolved with a well—designed
ar. executed quality control program. Chemical resistance
problems, however, remain a major unknown, due to the lack
of an adequate standardized testing program to date. The
overall significance of these technical problems is compared
to the significance of similar problems associated with
ciay liner and cap materials. (Reference #6, Section 4.0.)
Q—4. Should the regulations require that design engineers
evaluate FML manufacturers’ seaming processes as well as
field installation seaming processes, so that the entire FML
system is evaluated, not just the FML material as installed?
A. Based on the results of this study, factory seaming does not
generally present a problem for liner performance. However,
design engineers should be satisfied, by their own
investigation, that all seams are adequate. (Reference #10,
pp. 3—8 to 3—17.)
Q—5. Proper field seaming is critical to the integrity of FMLs.
A recent survey by Shultz and Mikias, March 1982, indicated
that manufacturers’ recommendations are not always followed.
Is there a need for more QA/QC?
A. Interviews with representatives of the liner industry and
with the design engineers produced general agreement that
present QA/QC programs are not always adequate to ensure
c’ompliance with the recomme-nded seaming procedures, and
that seaming is not always done under the specified weather
conditions. Recommendations have been made for requiring
extensive QA/QC for all liner installation. (Reference
#10, pp 3—8 to 3—19.)
Q—6. Present regulations restrict the thickness of a protective
layer over a synthetic liner to 30 cm, due to the maximum
leachate head requirement. Should the thickness of this
protective layer be increased to prevent damage to the
liner and leachate collection system? What material is
best for providing an intermediate layer?
A. It appears that a 30 cm protective layer is not thick enough
to protect the liner material and the leachate collection
system. It is recommended that EPA amend its regulations
to allow a thicker layer above a synthetic liner, since a
leachate head of approximately 60 cm is not likely to
cause increased seepage through a synthetic liner. (Reference
#4, Section 8.0.)
0—7. Does the one—foot head standard necessitate the placement
of the leachate collection pipes so close to the synthetic
liner that the liner may be punctured or otherwise damaged
during installation or operation of the leachate collection
system?
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A. The results of this study indicate that synthetic liner
damage may occur as a result of the 30 cm leachate limitation.
Based on these results it is recommended that the level
limitation be raised for synthetic liners. The 30 cm
leachate head limitations was developed to limit the
hydrostatic load. There appears to be no likelihood of
increased leakage associated with a higher head. iReference
*4, Section 8.0.)
(3) Leachate Release and Facility Failure — Questions 1—7.
0—1. For synthetic liner materials, do weak spots in “non—joint”
sections of the liner rupture and leak more frequently than
joints or sealed seams? If so, can they be identified
‘during construction and reinforced? Can weak spots be
located during active operations or before closure, and be
repaired?
A. Weak spots or material defects in synthetic liners do occur
and can cause liner failure. However, adequate testing of
tensile strength and tear resistance will identify any
defects, and proper on—site quality control procedures,
including visual inspection, will assure the integrity of
the synthetic liner material. Recommendations to OSW to
include such testing and quality control procedures in the
Part 264 regulations have been made. (Reference #4,
Sections 3.0 and 4.0.)
Q—2. What are the impacts and occurrences of the following during
synthetic liner installation; rips, tears, punctures,
weathering, and damage due to heavy equipment?
A. The adverse effects of weathering of synthetic liners during
construction are well known and constitute a significant
source of liner failures. The weathering factors include:
exposure to UV radiation from sunlight; exposure to ozone
and other oxidants or free radicals generated in the air;
high and low temperatures; expansion and contraction due
to changes in liner temperature (affected by air temperature
and sunlight); wind (causes wind—flap of FML); hail (can
puncture thin FMLs); and abrasion (from wind—blown sand).
Other failure modes include operations including heavy
equipment (especially cleated tractors) and punctures and
tears from roots, rocks, stumps, or surface irregularities.
(Reference *7, Section 4 and Reference #9, Section 7.)
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Q—3. The r€ gu1ations specify that the FML must be placed on a
“base capable of providing support...”. Must we also specify
the type of material, its construction, and its speci icat1ons
(permeability, etc.)? Is this, in effect, a double—liner (FML
over clay)?
A. The FML base material could be any matérial that adequately
supports and protects the liner from excessive stress.
Clay bases can be used for specific applications, but other
materials, such as natural soil, sand, etc., are also
acceptable. (Reference #10, pp. 3—5, 3—1 to 3—li.)
Q—4. What are the minimum specifications for the base of a
facility upon which a synthetic liner is to be installed so
as to ensure perpetual structural integrity of the liner
system through support by the sub—surface?
A. Minimum foundation specifications must be assessed based on
the local site conditions and the particular facility.
proposed. A geotechnical investigation of the site area is
required to adequately specify these conditions. (Reference
#10, p 3—5.)
Q—5. When requiring a specific synthetic liner, should EPA
specify the material to be used and the permeability of the
base upon which the liner will be installed?
A. This question was not specifically addressed by this study.
Q—6. Do any operations have experience with a double-lined
(synthetic) facility and leak detection systems? Can
leak detection systems be installed in a single—liner
f a cii i ty?
A. There is less than ten years operating experience for double—
lined flexible membrane lined facilities and a very limited
data base. Leak detection systems were not specifically
evaluated by this study.
Q—7. Summarize available information on synthetic liner failures
to determine the effect on liner performance (small, medium,
or large volumes of leachate leaking out).
A. This question was not specifically addressed by this study.
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IV. LOCATIONAL ISSUES
(I) Regulatory Requirements — Questions 1—7
Q—1. Should EPA regulations specifically address local geology
and hydrogeology when siting a hazardous waste facility?
Should such factors as high permeability sandy soils,
saturated soils, and mining of aquifers be considered?
A. - Based upon the results of the locational factors analysis, it
is recommended that EPA develop locational standards, as an
integral part of the final Part 264 hazardous waste facility
permitting requirements. These standards, which would
probably include the above factors, would provide performance
goals to be achieved at any potential facility site.
Determination of the adequacy of a potential site would be
done on a case—by—case basis. (Reference *5, Section 5.0.)
Q—2. EPA authorizes Regional Administrators to exempt facilities
from certain design and operating requirements b ? considering
certain parameters on a permit—by—permit basis. Should the
Agency establish hydrogeologic setting standards to be
considered in the granting of any exemptions?
A. Based upon the results of this project, it is recommended
that EPA develop facility location standards under Part 264
that include a consideration of the hydrogeologic setting.
The Agency agrees with this recommendation and wi] .I consider
various regulatory approaches in developing these standards.
(References #5 and #12, Section 6.)
Q—3. Would it be useful to implement location standards that
require a minimum level of on—site geotechnical investigations
and data collection to include soil borings, bedrocks, and
ground water conditions prior to siting?
A. The results of this project illustrate the complexity of
characterizing site hydrogeology. Detailed g otechnical
investigation will be required to adequately characterize
specific locations. (Reference #5, Section 5.1,
Reference #12.)
Q—4. Should EPA establish minimum “setback reqtirements”? In
other words, do surface distance requiromcnts (away from
residences, drinking water wells, surface water bodies,
etc.) guarantee any protection?
A. The issue of “setback” distances was not specifically
addressed by this project. Based upon the findings of the
technical location report and fate and tra’ sp rt modeling of
selected hydrogeologic settings, a minimum setback requirement
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for water bodies applied to all sites would be an inadequate
means of protecting public health and the environment.
What would be an appropriate distance in or c case could
be significantly less protective in another situation.
Potable ground water and surface water bodies that seem to
be ph rsically separated over long distances, for example,
may actually be interconnected as recharge and discharge
points of a very complex hydrogeological ZlOw:system. Each
flow system may be unique. For this reason, qsing
topographical surface distances to define a buffer of
protection is not effective. In the case of distances to
residential areas, the Agency will need to conduct further
studies before a minimum setback” can be established.
Q—5. Should a minimum depth to ground water below the facility
of 30 feet be established? Would this unsaturated or
vadose” zone provide protection to ground water by
attenuating contaminants, and act as an early warning system
for liner leaks by using unsaturated monitoring techniques?
A. Depth to ground water or thickness of the unsaturated zone
below a facility is a major factor in controlling travel
time of a contaminant to the ground water aquifer. The
significance of this thickness varies according to several
complex factors including geology, hydrology, and climate
of each particular location in which a facility is sited.
In arid regions, for example, there is a travel time
advantage gained by maximizing the thickness of the
unsaturated zone under -a facility. In humid areas, where
leachate release is greatqr and water tables are closer to
the surface, the travel time advantage realized from a
particular unsaturated zone thickness is small or non-
existent. The results of this project indicate that rather
than specifying a minimum depth for all cases, it is more
appropriate to evaluate local and regional hydrogeology in
terms of soil characteristics, rate and extent of ground-
water flow, and proximity to ground water discharge and
recharge zone. Appropriate facility locations should not be
selected solely on the basis of depth to ground water.
The potential for attenuation is commonly assumed to be
greater in unsaturated soils. More research is necessary
before this can be demonstrated in low permeability soils
for a broad range of che.nicals. (Reference #5, Sections 4,
12, and 13 )
Q—6. Should EPA develop locational standards that specifically
protect recharge areas of sole source aquifers?
A. A principal hydrogeologic locat onal factor examined in
this project was the geometry and dimension f a ground-
water flow system. Important sub—units are the
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positions of recharge and discharge boundaries within the
flow system. The position of a hazardous waste facility
with respect to these recharge nd discharge areas directly
defines what impact that facility will have upon the ground
water in the event that the contaminant fails. In developing
locational standards, the Agency may require characterization
of ground—water flow systems and a facility’s proximity to
recharge zones since the resuits of the recent modeling analysis
indicate the significance of tnis factor for safe and proper
siting. More detailed study is required to determine the
specifics of such a requirement. (Reference #12.)
Q—7. Should EPA restrict construction of hazardous waste facilities
in aquifer recharge areas, as well as in productive ecosystems
such as wetlands, prime agricultural areas, grazing lands,
forests, and critical habitats?
A. As a result of the analysis of locational factors, a.
recommendation has been made that EPA identify sensitive
locations, which may include those mentioned above, and
either restrict hazardous waste facility siting in those
locations or require additional design and operating safety
features to insure no unacceptable risk of environmental
contamination. (Reference #5, Section 5.0.)
(2) Hydrogeologic Settings — Questions 1—7
Q—1. Are there certain hydrogeologic settings that we understand
well enough to confidently predict flow rates of conserative
species and maximum dispersion over a given time period?
(Assumes we can specify a maximum time period that we feel
we need to assure protection.)
A. Based upon the results of the locational factor analysis,
it can be concluded that migration of conservative contaminants
and dispersion in the ground water can be simulated and the
results analyzed to better understand the consequences of
leachate release. This type of simulation was performed
in this project using some simplified, hypothetical,
hydrogeologic settings, and some simplifying assumptions,
for ]eachate characteristics. A more s phisticated analysis,
invloving more complex settings, can be performed provided
the appropriate data is available. This is a major drawback,
due to the fact that site specific data is not generally
available without a detailed site investigation, and that
certain key flow parameters, such as effective porosity and
dispersivity, are very difficult to measure in the field.
Extreme caution should be taken, therefore, in interpreting
the results of any ground water flow or contaminant transport
simulation. No attvmpt to predict actual contamination
concentrations should be made. (Reference #13, Section 5.0.)
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Q—2. What soil permeability and other hydrogeologic conditions
would result in vertical migration or migration against the
horizontal yradi’ ’-.t so that a reasonably well—placed
monitoring well would still be unable to detect ground water
changes?
A. Based on the results of the locational factor analysis, sites
with complex hy !rogeology (i.e., anistropic, heterogeneous
deposits, fault or fracture zones, etc.), or sites located
in discharge zones,, may present conditions in whichground
water flow patterns are difficult to determine. Under
these conditions, the proper placement of monitoring wells
may be difficult. Recommendations have been made to EPA to
investigate further these types of hydrogeologic formations.
(Reference #5, Section 5.0. )
Q—3. From a h ’drogeologic standpoint, what are the advantages
and disadvantages of locating a facility in a ground water
discharge zone? Can disadvantages be overcome by engineering
solutions?
A. From a hydrogeology standpoint, locating a facility in a
discharge zone provides an advantage .in that ground water
flow will tend to prevent migration of any jeachate away
from the facility. The disadvantages are that upward
hydrostatic pressure on the liner may result in installation
or operating problems, and that contaminant migration may
reach a point of discharge to a surface water body. While
various engineering solutionSmay be appropriate, any such
solution is basically a site—specific matter, and is,
therefore, not directly addressed in this project. (Reference
#13, Section 4.0.)
Q—4. How does one identify a location where precipitation does
not recharge ground water?
A. Basically, there are two conditions in which precipitation
does not directly recharge the ground water. An area with
significant relief (that is, steeply sloping terrain) will
result in surface run—off to lower elevations and eventual
drainage to a lake or stream. An area with relatively low
permeabiLity (a poorly-dLained soil) will allow a limited
amount of infiltration, and could result in net evapo—
transpiration, rather than ground water recharge. (Reference
#12, Section 3.0.)
Q—5. How is runoff defined? Is runoff due strictly to precipita-
tion? What are the effects of slope, relief, surface topography,
and vegetation? How far does surface accumulation of
preci ’itation have to move before it can be considered runoff?
A. This issue was not specifically addressed in this project.
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Q—6. What are the most crucial factors in specifying a region as
“arid”? Are they merely precipitation and evapotranspiration
or a”3rage annual precipitation? Are other more site—specific
factors such as slope and proximity to recharge/discharge
areas also dsed to define these areas?
A. In this study 1 EPA assumed that the range of climatic conditions
in ..his country could be represented by mean anntzal precipitation
for three selected weather stations. An average annual
precipitation of 15 inches per year was arbitrarily selected
to represent a semi-artd condition. “Arid” conditions were
not defined or analyzed as part of this project. Data for
average annual precipitation and evapotranspiration are the
principal factors generally relied upon to define “arid”
conditions. Other hydrogeologic factors can be used to define
arid” regions, however, these factors are considered secondary.
Most of the distinctive hydrogeologic features of arid regions
are related to the quantity of precipitation and subsequent
availability of ground water. With precipitation less than S
to 10 inches per year, most soils will cease to allow passage
of recharge water. The amount of available ground water
under these conditions will depend upon soil permeability,
specific retention of soil, and rainfall distribution in
relation to temperature. (References *5, and #13.)
Q—7. Will changes in the levels of the seasonal high water table
have an effect on the integrity of the liner system?
A. Any activities or conditions that effect the level of the
seasonal water table will have some influence on the potential
for rupture of an installed or in—place liner. Hydraulic
pressures directed upward against the base of a liner may
result in “piping” or “boiling” of the soil. A large upward
hydraulic pressure due to the rise of a water table may exert
sufficient stress upon the liner to produce cracks or fissures.
(Reference *12, Appendix C, Reference *9, pgs. 1.10—7.15.)
(3) Design/Location Interrelationships — Questions I and 2
Q—l. Is requiring a low permeable cap to prevent contamination of
surface water from runoff necessary in locations where there
are no surface water bodies near the facility or where the
region is so arid that annual precipitation is not capable of
causing runoff to surface waters?
A. The low permeable cap is fundamental in preventing precipitation
from infiltrating the landfill and minimizing the generation
of leachate. If the cap has a greater permeability than the
bottom liner, there is a tendency for the rain water that
infiltrates the landfill to build up and the bathtub effect”
may occur. In extreme cases, the perched water table can rise
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to the surface of the landfill and lead to overland flow to
the nearest stream tributary, resulting in contamination of
the stream water. The overland migration of leachate should
be discouraged in all situations. The absence of the
potential for contamination of a surface water body is
replaced by threatened ground water, terrestrial, and
atmospheric environments. Granted, in areas having very low
annual rainfall and high evaporative potential, bathtub
e’ffects may not develop during the operational and post—
closure care periods, even when the permeability of the cover
material is several orders of magnitude greater thar that of
the bottom barrier level. (Reference #1.)
Q—2. EPA currently requires installation of clay and/or synthetic
covers at closure to prevent a facility from filling with
leachate and overflowing (bathtub effect). Should a waiver
from this requirement be granted in certain locations
characterized by insufficient precipitation for creating the
“bathtub effect”?
A. In locations having very low annual rainfall and high
evaporative potential, bathtub or tarmac effects may not
develop during the operational and post—closure care periods,
even in cases where the permeability of the cover material is
several orders of magnitude greater than that of the bottom
barrier layer. Therefore, a waiver from the low permeability
requirement of the cap may be appropriate. (Reference #1,
p. 16.)
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