«.<*-
&EPA

United States
Environmental Protection
Agency   _
                     Solid Waste and
                     Emeraency Response
                     (5305W) '
                     EPA530-R-97-024
                     NTIS: PB97-1 76 861
                     January. 1993
Indexing  of Long-term
Effectiveness of Waste
Containment Systems
for a Regulatory Impact
Analysis; Draft
            g |. iPA Headquarters Library
               Malt code 3201
                     ! NW !
             Waihlngton DC 20460
      Printed on paper that contains at test 20 percent postconsumer fiber

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UNITED STATES         -   OFFICE OF SOLID WASTE         EPA/NUMBER
ENVIRONMENTAL PROTECTION   WASHINGTON, DC 20460       - JANUARY, 1993
AGENCY
    INDEXING OF LONG-TERM EFFECTIVENESS
     OF WASTE CONTAINMENT SYSTEMS FOR A
         REGULATORY IMPACT ANALYSIS
                      DRAFT COPY


                 A Technical Guidance Document
                     Office of Solid Waste
                U.S. Environmental Protection Agency
                    Washington, DC 20460

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INDEXING OF LONG-TERM EFFECTIVENESS
OF WASTE CONTAINMENT SYSTEMS FOR A
     REGULATORY IMPACT ANALYSIS
                     Authors
                Hilary I. Inyang, Ph.D.
             Senior Geoenvironmental Engineer

                   Guy Tomassoni
            Engineering Geologist/Hydrogeologist
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            Corrective Action Programs Branch
         Office of Solid Waste and Emergency Response
           U.S. Environmental Protection Agency
                Washington, DC 20460
                   November 1992
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                                                 DISCLAIMER
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                  This document is intended to assist U.S. EPA personnel in the assessment of long-term

             effectiveness of some containment systems for waste disposal.  It is not advocated that the

             content of this document be used as the sole basis for decision making.  However, this document

             sheds some light on the problems associated with the prediction of long-term effectiveness and

             presents one approach to relevant assessments.



                  This guidance is not a regulation (i.e., it does not establish a standard or conduct that can

             be enforced by law) and should not be used as such.  The contents of this document do not

             necessarily reflect the views and  policies of the U.S. EPA.  Also, mention of trade names,

             commercial products, or publications do not constitute an unqualified endorsement of their use.
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TABLE OF CONTENTS
Section . .
DISCLAIMER. 	 	 	 	 	 ; 	 ..; 	
TABLE OF CONTENTS 	 	 	 	 	
LIST OF FIGURES AND TABLES 	
1.0 PURPOSE 	 	 	 : 	 '. 	 '..... 	
2.0 INTRODUCTION 	 '.'. 	 	 	 	
3.0 APPROACH TO INDEXING..... 	 ; 	 	 	
4.0 INDEXING SYSTEM 	 	 	 	 	
4.1 CAPS 	 	 	 	 	 	 	
4.L1 Clay Caps 	 * 	 ; 	
4.1.2 Synthetic Caps 	 	 	
4.1.3 Composite Clay and Synthetic Caps..... 	
4.2 LINERS 	 ™. 	 \ 	 	 	 	 	
4.2.1 RCRA Subtitle C Composite Liner Systems 	 	
4.2.2 • Clay Liners 	 ;....; 	 	
4.2.3 Synthetic Liners 	 	 	 	 	 :..'. 	
4.3 Si IBSIIRFAfF BARRIERS 	 / 	
4.3.1 Slurry Walls 	 	 	 	
4.3.2 HDPE WALLS ;TT; 	 ; 	 	 	 	
, 5.0 SUMMARY 	 	 	 	 	 	 	 	 	 ;...-.

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iii
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	 	 3
4
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7
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	 " ..14
	 ... ' 15
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	 22
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	 ;.... 23
	 ; 	 23
25
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                                   LIST OF FIGURES
                                                                '*'"
Figujg '             ,       .           .     -                                    Page
  1  An illustration of long range degradation tracks of waste containment systems      6
  2  Summary of the one-dimensional freeze/thaw cycle effects on the Niagara
     Clay (Ziramie et al. 1992)                         ,            r              .9
  3  The setup of the Electrical Leak Location Method (Laine and Miklas 1989)     .    19
  4  A comparison of liner thickness equations (U.S. EPA 1984c)                . ,    20
  5  Simulations of cumulative diffusive solute transport through a hypothetical
     soil-bentoriite barrier (Molt and Weber, Jr. 1991)                                24
 .6  Types of locks for HDPE walls (Manassero and Pasqualini 1992)                 25

                                   LIST OF TABLES
Table
  1
  2
  4
  5
  6
Effectiveness of selected waste containment measures
Performance of barrier layer materials (adapted with modifications from
Koemer and Daniel 1992)
Overall benefit of each barrier configuration of cover/liner materials
determined by summing the horizontal rows in Table 2 (adapted with
modifications from Koerner and Daniel 1992)
Case histories of compacted clay liners (Daniel 1987)
Summary of experience with liner performance in the field (Bass et al. 1985)
Leak detection and location survey data for impoundments where the bottom
floor areas were surveyed (Laine and Miklas 1989)                     ~
 Page
 11

 13


..14
 16
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  1.0  PURPOSE                   .
      This document is intended to support a Regulatory Impact Analysis (RIA) required for a
 major Corrective Action regulation proposed by the U.S. Environmental Protection Agency.
 The  objective of the RIA is to evaluate  the  impact pf the proposed regulations  on the
 regulated community, and determine whether the regulations will  be protective of  human
 health and the environment  The effectiveness  indexing scheme described in this paper was
 developed to provide input data to a multi-media contaminant fate and transport model used
 in the RIA to assess the pollution potential  of ground water, surface water and soil. In view
 pf the fact that in certain situations, the proposed regulations  may allow on-site containment
 of hazardous wastes (e.g.,  capping) as opposed to treatment/destruction (e.g., incineration),
 an assessment of the long-term effectiveness of containment  systems is necessary. In such
 assessments, there exists the difficulty of predicting and verifying long-term effectiveness.
 This  problem exists because engineered waste  containment systems  have existed for a
 relatively short time in comparison with other engineering structures. Numerical estimates of
 design lives and effectiveness of containment systems have been made without the benefit of
 field data on the past performance of similar systems over a reasonably long time interval.

     Notwithstanding the  paucity of long-term  performance data on waste containment
 systems, numerical assessments are necessary for regulatory purposes.  Available  predictive"
tools  exemplified by models, mostly deal with initial conditions under the tacit assumption
that  constructed systems will exist at  the  same degree  of structural integrity over an
extended period of time.  Also, such models often  treat a few elements of the overall issue of
effectiveness.  Effectiveness is herein defined as the ability of the waste containment system ,

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to prevent
and direction.
the mobilization and transport of contained waste outside,the system in any phase
     A rating  (indexing)  scheme  has been  proposed  for assessing  the long-term
effectiveness of clay caps,  synthetic caps,  composite clay and synthetic caps, clay liners,
synthetic' liners, the Resource Conservation and Recovery  Act (RCRA)  Subtitle C  liner
systems, and vertical barrier walls. The indexing system is based on a review of literature on
     ,                                   _                                        \
initial and potential performance indices of the structures mentioned  above..  Due to the
existence of gaps  in available information, technical judgment has been introduced into the
selection process  of specific rating numbers for long-term effectiveness.  One of the most
widely used models—the Hydrologic  Evaluation of Landfill Performance (HELP) model
 allows the input of a "failure rate," which the user specifies on the basis of his/her judgment.
This allowance is an acknowledgment of the uncertainties associated with predicting the field
 scale  performance of facilities over time frames as long as  one hundred  years.  The rating
 scheme proposed is based partly on  subjectivity. It should be recognized as a rating scheme
 as opposed  to a numerical model.  Refinements may be necessary on a site-specific  basis,
 especially, when conditions are such that specific parameters of long-term effectiveness of
 the entire containment system can be reasonably analyzed in greater, detail.

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1
 2.0  INTRODUCTION
      It is generally known that the structural integrity of waste containment systems usually
 degrades as. time  progresses.   This  situation stems  from environmental conditions which
 induce  stresses on various components of the  system.  The root causes of these stresses
 include  thermal processes, biologic  processes, geostatic and geodynamic  loads, physico-
 chemical interactions between waste constituents  and containment  system  materials,
 sunlight, and hydraulic processes.  The rate at which the effectiveness of a containment
 system is affected  over a given time period depends on the conservatism of the initial design,
 quality control during implementation activities, and the frequency of facility maintenance.

     Ideally, it would be desirable to develop a "macro-model"  that comprises sub-models,
 each of which treats the decay of the effectiveness of specific components of containment
 systems  with time. • Unfortunately, containment systems comprise many  components in too
 many configurations in numerous hydrological settings.  The relatively short experience with
 modern  waste containment systems is such that  there are too many  unknowns. Each
 component of a containment system is susceptible  to a different degree,  to the  stresses
 mentioned above.  For example, polymeric materials of a geomembrane are more susceptible
 to ultraviolet radiation than clay liner  materials.  Furthermore,  the burrowing activities of
 rodents may introduce defects into the system in the long term.  The uncertainties associated
 with the  physical response of the entire containment system to the synergistic stresses from
 various  physical, chemical and biological processes  plague the development of a useful
 "macro-model" for precise prediction of the loss, of effectiveness of containment systems with
 time.  In essence, such models might not attain a level of accuracy that supersedes that  of a
numerical indexing  (or  rating) scheme that is based on a non-quantitative analysis of

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                                             /
 available prediction  schemes, test results  and configuration of containment systems.  The

 latter approach is adopted in this work.  Similar approaches .have also been adopted by
               f            ^
 others, e.g., Koerner  and DanieP(1992).
            .         *                  '   '             «          •                 v


 3.0   APPROACH TO INDEXING               ,      '    .

     It 'is  desirable  that  waste containment systems remain effective  for a long time,

 reasonably, beyond the closure period.  The  design life of a facility should be as long as

 necessary to effectively restrict hazardous constituents from becoming a threat  to  human

 health and the environment. The durability of various components of containment systems in

 the laboratory have been investigated vigorously only, in the past fifteen years. Experimental
                                                                /
 and modeling approaches to assessing long-term effectiveness have been adopted in such

 studies.  Although these  investigations have shed  light  on the significant processes and

 potential responses of individual components over extended periods, the  overall  long-term

 effectiveness of composite systems still remains  a gray  area.  It  may not be feasible to

 develop and verify a complete and precise numerical relationship between the effectiveness of

 composite  systems and time-since-constmction.   Considering the diversity of possible

configurations,  hydrogeological conditions, and waste  types,  coupled  with .various

maintenance frequencies, such an approach would require  an extensive factorial experiment.
          \        .'*•''
It should also be noted that some of  the relevant factors cannot be fully controlled.  For

example, the hydrogeology of a site is not normally controllable.



     The approach adopted.herein is to use available information on modeling approaches,

laboratory  experiments and field studies to develop a  reasonable indexing  system for

evaluating the long-term effectiveness  of waste containment systems for RIA purposes.  In

this approach, the entire system is considered rather than a single component  However, the

entire system can comprise only one component in  some  cases.  For  multi-component

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 systems, the degradation or failure of a single component does not necessarily mean that the

 entire system is completely ineffective,



      In this approach, the effectiveness of a containment system is assumed to  vary with
                                                                                       i

 time  as illustrated in Figure 1. The figure also illustrates the .potential gain in effectiveness

 that occurs with the implementation  of an adequate maintenance scheme.  A similar concept

 has been applied in the development of serviceability index for highway pavement structures,

 most of which comprise many components.  When built initially, the  containment system has

 an effectiveness, Eto, which depends on the conservatism of the design and the adequacy of

 the construction quality control. Over time, the effectiveness decreases along curve A. For

 example, at time  t2, the corresponding  effectiveness is E(2.   However, if maintenance

 activities are implemented at time ti, the effectiveness improves to the level Eti and system
                        ,

 degradation follows curve B.   The time horizon, t
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system. Nevertheless, such information has been reviewed and taken into consideration in

the selection of degradation rates proposed herein.
      Figure!.
        Tlnw Sine* Construction, t (y*ars)


An illustration of long range degradation tracks of
waste containment systems

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 4.0    INDEXING SYSTEM
     The proposed effectiveness-time relationships are summarized in Table 1 for various
 configurations of waste containment systems.  The time periods selected  are 0 years,  10
 years, 30 years and 100 years.  The technical issues discussed above have been considered.
 Pertinent technical  literature has also been reviewed.  Existing models, experimental data
 and  verbal propositions have  been considered:  In most cases, judgment is used in the
 analysis and adoption of information reviewed by the authors of this proposition. It should be
 emphasized that although the degradation-time relationship is influenced by the initial design
 of a waste containment system, design approaches are not the direct focus of this discussion:.
 For more information on that aspect,  the reader is referred  to relevant documents such  as
 Richardson and Koemer (1989), and U.S. EPA (1984a. 1985a,  1989a and 1989b) for covers
 and lining systems; Millet  and Perez (1981), Barvenik et  al (1985), Morgenstern and Amir-
 Tahmasseb (1965), Mott and Weber, Jr. (1992), D'Appolonia (1980) and U.S.  EPA (1984b)
 for slurry walls; and May  et al. (1985), Camberfort (1977),  Weaver et al. (1992), Ran and
 Daemen  (1992), USAGE (1973 and 1984), Van Impe (1989), Hausmann (1990) and U.S.
 EPA (1985b) for grout curtains.
                      ('                                             •  '
4.1   CAPS
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     Low permeability caps are used to cover waste materials to minimize contaminant
migration on the land surface, through the air, and into the ground water. Caps protect ground
                          i                                          i
water by  minimizing  the  infiltration .of precipitation into the waste which can mobilize
contaminants through leachate generation.  There  are a variety of cap designs and capping
materials  available.  Typically, a design will include  a  single or  multiple layers of low-
permeability natural clay or made-made materials (geosynthetic membrane).  Generally, all

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 designs include a high permeability drainage layer above the low-permeability layer(s) to
 promote precipitation  runoff.  All designs also include a vegetative layer  or some other
 material placed above the drainage layer to minimize erosion.  The discussion of effectiveness
 presented below focuses on the low permeability layers and refers to the ability of the cap to
 restrict infiltration of water into the underlying waste.

 4.1.1 Clay Caps
     The factors which may reduce the effectiveness  of clay caps include subsidence, slope
 instabilities, desiccation cracking, burrowing activities of rodents, and vehicle loads.  For the
 clay cap, effectiveness is herein defined as its ability to prevent the intrusion of moisture into
 the contained waste.  For a given set of hydrological conditions, the quantity of leachate
 generated is directly proportional to the effectiveness .of the clay cap. The latter depends  on
 both intergranular flow (pore flow) and flow through flaws which may result  from any
 combinations of the phenomena stated earlier.  Due to the uncertainties associated with the
 occurrence of degradation events with time, an exact predictive relationship is difficult to
 develop and verify.  Models exemplified by the Hydrologic Evaluation of Landfill Performance
 (HELP) computer model predict pore flow only.  In Figure 2, increases in the permeability of a
compacted clay soil layer due to several cycles of freezing and thawing are illustrated.

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                      10*
0 DftY
0 OPTIMUM
* WTT
                               0    5   10    15  '26  25   30   35

                                NUMBER OF FREEZE/THAW CYCLES
      Figure 2.   Summary of the one-dimensional freeze/thaw cycle effects on
                  the Niagara Clay (Zimmie et al. 1992)



     Such changes iir permeability may be attributable to  the generation of fissures, etc.

When macro-flaws develop in  a clay cover over an  extended time period, Darcy, flow

relationships become inadequate for predicting moisture percolation.  Using the approach
* '                                        •                        -      '  '•
proposed by Anderson et al. (.1991), the macrofissures increase the hydraulic conductivity of

the soil layer by the amount given in equation (1).


                    K = R4pg/8uE>2
     (1)
                         K  =  hydraulic conductivity
                         R  =  radius of the channels
                         g  =  acceleration due to gravity
                         u  =  viscosity of ordinary water
                         D  =  spacing of the channels
                         p  =  density
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                                                                                        1
     In Table 1, a clay, cap  that meets minimum standards with  respect  to  hydraulic
conductivity, thickness and construction quality control is assigned an initial effectiveness of
80%.  It is assumed that significant flaws exist even in the initial post-construction period of
such cover materials.  Consistent with the degradation-time pattern often observed in most
engineering structures, it is assumed that the effectiveness will decrease exponentially with
time.      '                            ,
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    . It is  estimated  that  over a service  life of  ten years  immediately  following  their
implementation, the effectiveness of the  clay cap will drop  to 75%.  The probability of
occurrence of phenomena that cause flaws increases as the duration of service increases.  At
30 years, the effectiveness of the clay cap is estimated to be  60%.  It is roughly estimated
that after  100  years of  service, settlement,  rodent activity,  etc., would reduce the
effectiveness of single clay covers to 20%.
           >   i                                         .
     Note, however,  if  an  additional.clay cap  is  added to the system at 100 years, the
effectiveness goes up to  85%. Replacing the cap at such a time when the original cap is no
longer effective is consistent with 'the understanding that engineered structures  will not last
in perpetuity.  Furthermore, adding a new cap also reflects the premise that, unlike a liner
system, a cap can be easily maintained and, if necessary, replaced, without actually removing
the waste.   Adding a new cap also  reflects the need to provide long-term reduction of
leachate generation.             .

4.1.2 Synthetic Caps
     Holes can be introduced into synthetic caps of waste  containment  systems during
installation. Geomembrane caps may also be degraded by subsidence, ultraviolet radiation,
    \                                    •           .     .  ,          •
thermal stresses  and the burrowing  activities  of animals.  Temperature effects  on the
                                          10

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 durability of polymeric materials-have been  described  using  methods  based on the Rate
 Process Analysis (Koerner et al., 1990; and Kanninen, 1992). However, the effectiveness of
 a synthetic cap material in the field is a function of temperature as well as radiation and other
 unpredictable events.  Nevertheless, Koerner and Daniel (1992) rate a single geosymhetic
 cap above a single clay cap in terms of overall effectiveness. Relevant information is provided
 in Tables 2 and 3.  Considering the factors rated in Tables 2 and  3 and those discussed above,
 a single synthetic  cap is assigned an initial effectiveness of 90%.  This rating  takes into
 account the possible existence of imperfect seams  through which water can pass.
                                              j.
      Unavoidably, the volume of holes increases in synthetic layers over time.  Increases in
 the hydraulic conductivity of such layers should be expected. The increase in the discharge
 (flow rate of such covers due  to  the  presence  of large holes) can be estimated  using
. Bernoulli's equation as follows.             '
 Q = Ca(2gz)0-5
(2)
      Q  = discharge (m3/s)
      C  = dimensionless coefficient that pertains to the shape of the edges of the opening
            (approximately 0.6 for sharp edges)
       a  = hole surface area (m2)             ;                         .
       g  = acceleration due to gravity (9.8 m/s2)
       z  = depth below water level; may be approximated by the design head of infiltrating
            water (m).
     In the'indexing system proposed in Table 1, the effectiveness of a single synthetic cap is
assumed.to  be 15%  after 100 years.   This assumed effectiveness  is  greater  than  the
assumption made" in U.S. EPA (1982) that after 100 years, a synthetic cap will be completely
ineffective.  The  15% effectiveness is  based on the assumption, that synthetic caps will
                                          12

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       Table  3.   Overall benefit of each barrier configuration of coverAiner
                  materials determined by summing the horizontal rows in
                  Table 2 (adapted with modifications from Koerner and Daniel
                  1992)
Design
Alternate
Description
Overall
Benefit
Estimated Cost
(dollars/sq. ft.)
Benefit/Cost '
Ratio
Ranking in
Group
One Barrier Layer
A
B
C
CCL
GM
GCL
36
64
46
6.70
0.70'
0.70
51
91
66
• 3 .
1
'2 , ,
Two Barrier Layers
. D
E
GM7CCL
GM/GCL
58
66
1.40 .
. 1.40
41.
47 ••
2
1
Three Barrier Layers
F
G
GM/CCL/GM
GM/GCL/GM
71
77
2.10
2.10
34
37
2
1
CCL     =  Single compacted clay liner.
GM      =  Single geomembrane.
GCL     a  Single goesynthetic clay liner.
GM/CCL  B  Two-component composite.
GM/GCL      - Two-component composite.
GM/CCL/GM  = Three-component composite liner.
GM/GCL/GM  = Three-component composite liner.
degrade over time, but due to improvements in polymeric material technology, degradation
will not occur quite as fast as originally predicted by EPA.  If a new synthetic cap is installed
at 100 years, the effectiveness of the synthetic cap is assumed to return to the original 90%
estimate.                       -
                                                  • ,»       '   '

4.1.3 Composite Clay and Synthetic Caps                       ,
                                                                         N.
     The processes and assumptions described above for clay caps and synthetic caps apply
to the composite clay and  synthetic cap; however, the composite cap yields a greater
effectiveness than  the additive effectiveness of the two individual layers.  The clay layer
underlying the geosynthetic cap acts as a low premeable barrier for leakage through holes in
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 the geosynthetic layer.  Furthermore, the effectiveness of the clay-layer improves in this
 composite system because the synthetic affords  some  protection against the processes
 (discussed in section 4.1.1) which degrade clay caps. As indicated in Table 1, the initial
 effectiveness of the composite cap is assumed to be 95%.  At 100 years, the effectiveness of
 the composite system is reduced to 35%.  At 100 years, it is assumed that an entirely new
 composite cap will be installed resulting in an effectiveness of 98%. The increase, from 95% to
 98% is assumed to be due to the residual effectiveness of the original clay layer.
  .                                      '*"     -          '
 4.2  LINERS
     Liners for waste containment systems are generally intended to prevent the migration of
 hazardous constituents into the underlying subsurface. Liners are generally constructed of
 low premeability soils (clay),  geosynthetics, or a composite system consisting ,of both  clay
 and geosynthetic membranes.

 4.2.1 RCRA Subtitle C Composite Liner Systems
     The RCRA Subtitle C liner system consists of both clay and  polymeric layers.   The
 minimum requirements for this liner system includes from top to bottom, a leachate collection
 system, a primary  (upper) geomembrane, a leachate detection system, and a  secondary
 composite liner  consisting of an upper geomembrane directly overlying a clay layer.  In
contrast to the situation with caps, leachate compatibility becomes  more significant but
settlement (or subsidence) effects become less significant.  In developing the effectiveness-
time estimates contained in Table 1, it is assumed that there is no cover over  the buried
waste or contaminated materials.  Since the RCRA Subtitle C  liner is  a multi-component
system, the failure of one component does not necessarily imply that the whole system has
become entirely ineffective. Some failures of single and multi-component lining systems have
been reported.in literature.  Unfortunately, information is scanty or non-existent on the time
                                         15

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        Table 4.    Case histories of compacted clay liners (Daniel 1987)

 Location of
     Site
       Nature-of Liner
Actual Field k
   (cm/sec)
                         Reference and Comments
   Central
    Texas
 2-acre (0.8 ha) Liner for
 Impoundment; l-ft-(30-cm)
 Thick Liner Built of Local Clay
 Soil
   4 x 10'5
  (originally)
   Sx'10'6
(Reconstructed)
              Daniel (1984). Original liner may have desiccated
              somewhat. .Reconstructed liner not subjected to
              desiccation.  Poor CQA.  Liner retained fresh
              water.                        .
  Northern
    Texas
 25-acre (10 ha) Liner for
 Impoundment;  8-in-(20-cm)
 Thick Liner Built from
 Sand/Bentonite Mixture
   3 x 10'6
              Daniel (1984). Virtually no CQA.  Liner retained
              slightly  saline water.
   Southern
    Texas
 1-acre (0.4 ha) Liner for
 Impoundment; Liner was 2-ft-
 (30-cm) Thick and Built with
 Local Clay Soil
   1 x 10
         r5
              Daniel (1984). Liner retained brine solution.
              Little CQA.
  Northern
   Mexico
Test Liner SO x 50 x 0.5 m and
Built with Local Clay Soil
 Ix 10-
                Auvinet and Espinosa (1981) and Daniel (1984).
                Good CQA.  Liner tested with fresh water.
 Texas A&M
  University
Prototype Liners; Each
Prototype Measured 1.5 x 1.5 x
0.15 m; Soils Consisted of
Kaolintte, Mica, and Bentonite
Blended with Sand
   1 x :10'6
      to
  •1 x 10:5
              Brown. Green, and Thomas (1983). Good CQA.
              Soil compacted with hand-operated equipment.
              Liquids were xytene and acetone wastes.
University of
 , Texas at
   Austin
Two Prototype Liners; Each
Liner Measured 20 x 20 x 0.5 ft
(6 x 6 x 0.15 m) and Was.Built
of Local Clay Soil
   4 x 10"6
     and
   9 x 1
-------
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 at which the reported failures occurred. Daniel (1987) reported case histories of clay liner
 performance in the field.  Pertinent information is provided in Table 4.  Bass et al. (1985)
 provide the data shown in Table 5  on the failures and successes  experienced with various
 configurations of lining systems.  Some of the configurations described in Table 5 are similar
 to  RCRA Subtitle C  liners.   Although the data presented in  Table  5 have  not  been
 incorporated in any direct numerical manner into  the indexing scheme  of Table 1, they do
 illustrate the fact that  some lining  systems do fail unpredictably with time.  Information
 provided by Daniel (1984) indicates that the actual  hydraulic conductivities of four clay liners
 in Texas are generally ten to a thousand times higher than those  measured on^ samples in the
 laboratory.  Bonaparte and Gross (1990) have presented data on  the field performance of
 double-liner systems within four to five years of their construction.  Some of the measured
 leakage  rates are attributed to the consolidation of the clay layer component of the lining
 systems investigated.   For geomembrane layers of liner systems, Giroud and Bonaparte
 (1989a and b) suggest the use of a hole frequency of 2 to 5 holes per Hectare and a hole size
 of 3 x l(Hm2 to compute flow rates.                                                   .

     Using the electrical leak detection technique  illustrated in Figure 3, Laine and Miklas
 (1989) surveyed 61 new or operating waste storage facilities in  which geomembrane .liners
are used.  An average of 3.2 leaks per 10,000 ft2 within a range of 0.3 to  5.0 leaks per 10,000
ft2 of liner .was  detected. Relevant data for bottom  floor areas of impoundments surveyed are
presented in Table 6:  Of all leaks, 87% occurred through seams while the remainder occurred
          i ,                      '  *           •       ,
through internal areas  of the geomembranes. Observed flaws ranged from circular holes of up
to 1 inch in diameter to slits from 0.25 to 12 inches in length. Sometimes, flaws as large as 48
square  inches Were observed.                                            ,
                                          18

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                      RIMOTI
                      CURRENT
                      RETURN
                      ELECTRODE
CURRENT SOURCE
 EUCTRODE
                                                   MOVING •
                                                  MEASUREMENT
                                                  ELECTRODES
                               CURRENT
                              FLOWUNES
       Figure 3.   The setup of the Electrical Leak Location Method (Laine and
                  Miklasl989)
     Considering all the factors and data discussed above, the RCRA Subtitle C liner system
(multi-layered) is assigned an initial effectiveness of 98% as indicated in Table 1. In U.S.
EPA (1983), 1% of the area of the synthetic layer component of the lining system is assumed
to have the same vertical  permeability as the, underlying soil.  This corresponds roughly to
99% effectiveness.  However, considering the uncertainties in the distribution of holes at
geomembrane seams, spatial variabilities in the hydraulic  conductivity of the clay layer
                                                                 '   ^ \  ,
component of the system, an initial effectiveness of 98% is assigned in Table 1.  By the end of
the tenth year of operation, significant leakage would occur through the upper geomembrane
barrier of  the lining system.   Assuming that  some flaws  would, have developed in  the
secondary  geomembrane  and  the. underlying clay layer in  ten years, there  would be  the
possibility of seepage of fluids  through the system.  Considering this  situation,  the
effectiveness of the system after 10 years is rated at 95%. Within the first 30 years, leachate
that passes through degraded membranes  and the drainage layer could also travel through
relatively intact portions of the clay layer component of the system by intergranular (pore)
                                          19

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flow and/or diffusion.  For a clay layer thickness of up to 35 cm (about 13.8 in.), analyses of


fluid  transit  time predictions by U.S. EPA  (1984c) using various percolation equations


indicate  that transit  times would generally  be under  one year.  These predictions are
                     /
presented in  Figure 4.  It should be noted that  only the  times of first arrival  of retained


substances are predicted.   Similar analyses by Shackelford (1992) for a 91 cm (35.83 in.)


thick clay layer  indicate breakthrough  times ranging from  2.6 to 9.8 years for  various
                                «nd
                    10*  •£t«r Hilly 1982
             - — -- traniit ciM •elatioM (M* cm)

                     j	 „ .
                                             Q Ma4ifi«d tnatic timt •quctioo


                                             O CtMa-ta»t U»U)
                              10         19       20
                                   LINCM THICKNESS d . «m
       Figure 4.  A comparison of liner thickness equations (U.S. EPA 1984c)
                                          20

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Table 6.      Leak detection and location survey data for impoundments where
             bottom floor areas were surveyed (Laine and Miklas 1989)
the
Survey No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
, 38
39
40
41
42
43
44
45
46
47
TOTALS
S
Size
Sq. Feet
958
958
958
1. 000
1,798
2,625
3,000
3,000
3,200
4.951
4.951
4.951
5,175
7,007
12.600
18,346
26,016
.26,016
27.297
32,292
43,560
45,345
50,000
50,400
54,500
55.025
58.900
62.500
64.583
65,340
65.369
65.369
65,369
65.500
65.500
74.088
82,500
87,120
87,120
99,050
135.036
150.781
152,460
152,460
157.584
164.085
362,690
2,769,336
Total
Leaks
2
. 3
3
4
0
6
'21
4
0
0
17
2
2 .
4
7
50
7
4
8
25
2
4
6
193
29
12
8
21
29
56
6
. 7
5
7
5
20
18
8
17
18
17
64
' - 2
- 7
12
18
51
811
- Leaks Located In
Bottom Seam Sheet
2
3
3
4
0
6
21
4
, 0
0
17
2
2
4
7
50
7
4
8 '
25
2
4
6
193
29
12
8
21
29
56
6
7
5
7
5
20
18
8
17
18
• 17
64
2 •
7
12
18
51
811
2
3
3 •
3 '
0
6
21
• 4
0
0
17
' 2
1
4
7 .
35
7
4
6
25
2
4
6
188
18
12
6
19
, 21
55
6
5
3
'. 5
3
19
15
7
17.
14
16
46
2
7
10
16
. 37
709
0
0
0
1 . -
0
0
0
0
0
0
0
0
1
0
0
15
0
0
2
0
0
. 0
0
. 5
11
0 • •
2
2
8
1
0
2
2
2 .
2
1
3
1 '
0
4
1
18
0 .
0
2
. 2
14
102
Leaks Per
10, 000
Sq. Feet
20.9
31.3
31.3
40.0
0.0
22.9
70.0
13.3
0.0
0.0
34.3
4.0
3.9
5.7
5.6
27.3
2.7
1.5 ,
2.9
7.7
0.5
0.9
1.2
38.3
5.3
2.2
1.4
3.4
4.5
8.6
0.9
1.1
0.8
1.1
0.8
2.7
2.2
0.9
2.0
1.8
1.3
4.2
0.1
0.5
0.8
1.1
1.4
2.9
                                     21

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      assumptions of concentration ratios and  relative fluxes of solutes at the bottom end of the
      clay liner.  The latter analyses also indicate that maximum solute flux through the same clay
      liner would be attained in 83 years.

          It should be noted  that the data and predictions obtained for the cases discussed above
      do not necessarily apply to all cases.  However, information  on the range of breakthrough
      times  exemplified by the  preceding discussions  has been considered in developing  the
      effectiveness index for RCRA Subtitle C liners shown in Table 1:  In the  indexing scheme
      presented in Table 1, the RCRA C liner system is rated at 85%. and 60% effectiveness at 30
      and 100 years of operation,  respectively.

      4.2.2 Clay Liners
 j        The processes and findings described in section 4.2.1, pertaining to clay liners, result in
                              ••  '•    '                    '             ,         •
      an assumed initial effectiveness for a single clay liner of 70% (see Table 1).  After 100 years,
  *    the effectiveness of this liner is reduced to 5%.
                    •v   "   f                       ,
• -*              •    '    '"'.•'••'      ''-''•'
  -'    4.2.3 Synthetic Liners                      ,             .                .
 ,j        The processes and findings  described in section 4.2.1, pertaining to  synthetic liners,
      result in an assumed initial  effectiveness for a single synthetic  liner of 85 percent (see Table
                                   -*'•__;'.
 -:    1). Contrary to the single clay liner which retains some level of effectiveness at 100 years, it
      is assumed that a single .synthetic liner will be completely ineffective (0%) at this time.  This
      assumption is based on the  fact that once the number and size  of holes in the synthetic liner
      reaches a certain level, all infiltrating liquids will likely move along the liner to low points in
      the system. If these low points conincide with holes, then the liner will provide no barrier to
      leakage.      .                   '         .                          -
                                               22

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i
1
t
f
 I
 4.3  SUBSURFACE BARRIERS
     The term subsurface barriers refers to a variety of low permeability cut-off walls or
                         \
 diversions installed below ground to contain,  capture, or redirect ground- water flow.
 Subsurface barriers are commonly used at hazardous waste sites to constrain or restrict the
 migration of contaminants from  a designated area.  To date,  the most commonly used
 subsurface barriers at hazardous  waste sites are slurry walls.   Barriers used in the RIA,
 however, also include high density polyetheiene (HDPE) interlocking sheets.   Although
 relatively new in the. market place, these HDPE walls appear to be a viable and effective
 alternative to slurry walls for certain applications; therefore, they have been included in the
 proposed indexing system.

     The effectiveness-time relationships shown in Table 1 for HDPE walls and slurry walls
 are proposed assuming no intervening barriers like liners and covers. This implies that these
 walls would be the first  barrier layers against the migration  of contaminants.   The
 effectiveness of a particular barrier wall depends on site conditions, mix design of wall
 materials (for slurry walls), joint integrity (for HDPE walls), wall thickness, durability of wall
 materials to  chemical attack, and the quality of construction.   The  effectiveness  indices
 proposed for barrier walls-in Table 1 are very general.  Owing to the novelty  of this
 containment technology, most of the available data are predictive in nature. Sufficient time ,
 has not elapsed for their verification in the field. The examples illustrated herein are also
 provided to indicate the numerical regime of the decay of effectiveness with time. Conditions
    1 <         " '•' ,                                             "                    ,
 vary widely; hence, the examples provided may not apply to some  specific cases.
        '      •                      '                  " ' '                        '     c
 4.3.1 Slurry Walls                                                    ,
     In Table 1, the initial effectiveness of slurry walls is rated at 70%. This rating roughly
reflects the difficulties associated with controlling the in-situ permeability of the slurry during
                                                        23

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'construction.  Owing to the segregation of materials, zones of excessive permeability often
 develop.  Over  a period of 10 years, the quantity of materials that diffuse across the barrier
 would perhaps be significant.  A pollutant detention time of 30 years would be sufficient to
 allow the physico-chemical interactions between contaminants and slurry material to cause
 increases in wall permeability.  At 30  years, the assumed effectiveness  of, slurry walls is
 reduced to 20%. With the addition of a new wall, however, the effectiveness could be brought
 back to the original 70% effectiveness.  Figure 5 is an example  of the projections of solute
 transport across soil-bentonite barriers made by Mott and Weber, Jr. (1991). By the authors'
 estimation, slurry walls may not be effective after a hundred years of service, (0% effective).
 Pertinent failure mechanisms are discussed by U.S. EPA (1984d).
                      OJ

                      0.7

                      0.6

                      05-
• D,» 0.635 xKT5,  £ = 0.38
• D,«O.S3SxlO-s.  E = 0.«
A 0,« l.07xl
-------
4.3.2     HDPE Walls                    '

                                                                           ;
     The effectiveness of HDPE barriers should depend largely on the tightness of the bonds

between adjacent sheets.  Manassero and Pasqualini have furnished illustrations of various

bond configurations as shown in Figure 6.  HDPE walls are perhaps the  newest vertical

barrier technology.  Hence, long-term performance data are not available  on them.  The

proposed numerical  indices which are tabulated in Table 1 are for single vertical sheets

without complementing slurry walls.  The initial rating is 65% (lower  than that of slurry walls)

but the effectiveness decays at a  much slower rate with increase in time.  This pattern is

chosen to be consistent with the  fact that HDPE walls are not susceptible to most of the
                    1                                '                        .
failure mechanisms that plague slurry walls.  At 100 years, the effectiveness ,of HDPE walls

is assumed to be reduced to the extent (25%) that the installation of  a new wall would likely

be warranted.  This installation should increase the effectiveness back to the  original 65%

level.
      Figure 6.   Types of locks for HDPE walls (Manassero and Pasqualini
                  1992)
                                         25

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5.0 SUMMARY         .
              *°                              '. ,
     In this document,  some  of the  technical issues  that  pertain  to  the long-term
effectiveness of waste containment systems have been discussed.   A conceptual model of
effectiveness decay  with  service life has been described  and illustrated.  Based  on that
model, a numerical rating  scheme which can be used in a Regulatory Impact Analysis (RIA)
                                              i
as well as other projects has been developed.  The reader is reminded that the scheme is a
rating system developed on the basis of a review of available literature and the technical
judgment of the  authors.   It is general  in  nature, and a particular facility can exhibit a
degradation pattern that reflects the curve configuration pattern of Figure 1 but defies the
rating scheme.  In essence, the proposed  scheme will be refined as more field data become.
available for use with models to fill the information gaps that currently exist
                                         26
I
  .-,
I
I
I
I

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 6.0 REFERENCES

 1.     Anderson, D.C., Lupo, M.J.,.Rehage, J.A.; Sai, J.O., Shiver, R.L., Speake, R.C., Brown,
         K.W.,  and Daniel, D.  1991.  Factors controlling minimum soil liner thickness.
         Project Summary EPA/600/S2-91/008.  Risk Reduction Engineering Laboratory,
         U.S. Environmental Protection Agency, Cincinnati, Ohio.

 2.     Barvenik, M.J., Badge, W.E., and Goldberg, D.T.  1985.  Quality Control of hydraulic
         conductivity and bentonite content during soil/bentonite cutoff wall construction.
         Proc. of the llth Annual Research Symp., Cincinnati, Ohio,'pp. 66-78.
 3.     Bass, J.M., Lyman, WJ. and Tratnyek, J.P.  1985. Assessment of synthetic membrane
         successes and failures at waste  storage and  disposal sites.  Project  Summary
         EPA/600-S2-85/100. U.S. Environmental Protection Agency, Cincinnati, Ohio.

 4.     Bonaparte, R.  and  Gross,  B.A.  1990.  Field behavior of double liner systems.
         Proceed,  of ASCE Symp.  on Waste  Containment Systems,  San  Francisco,
         California, pp. 52-83.                                          ;
 5.     Camberfort, H.  1977. The principles and.application of grouting. Quarterly Journal of
         Engineering Geology, Vol. 10, pp.  57-95.
 6.     D'Appolonia, DJ.  1980. Soil-bentonite trench cutoffs.  Journal of the Geotechnical
         Engineering Division, ASCE, Vol.  106, No. GT4, pp. 399-417.
 7.     Daniel, D.E.  1984.  Predicting hydraulic conductivity of clay liners.  Journal of the
         Geotechnical Engineering Division, ASCE, Vol.  110, No. 2, pp. 285-300.
 8.     Daniel, D.E. 1987;  Earthen liners for land disposal facilities. Proceed, of ASCE Conf.
         on Geotechnical Practice for Waste Disposal, Ann Arbor, Michigan, pp. 21-39.
9.     Giroud, J.P. and  Bonaparte, R.,  1989a.  Leakage  through liners constructed with
         geomembranes -  Part I.  Geomembrane liners. Geotextiles and Geomembranes,
         Vol. 8, No. 1, pp; 27-67.
 10.    Giroud; J.P. and  Bonaparte, R,   1989b.  Leakage  through liners constructed with
         geomembranes - Part II.  Composite liners.  Geotextiles and Geomembranes, Vol.
         8, No: 2,0^78-111.
 11.    HausmaiUV, M.R. * 1990. Engineering principles of ground modification.  McGraw-Hill
       _, publishing Company, New York.                                               .
12.    Kanninenr M.F.  1992.  Assuring the durability  of HDPE geomembranes.  ASTM
         Standardization News. pp. 44-49.                                       -
13.    Koerner, R.M., Halse, Y.H: and Lord, A.E.  1990. Long-term durability and aging of
         geomembranes.  Proceed, of ASCE Symp.  on Waste Containment  Systems, San
         Francisco, California, pp. 106-134.
                                        27

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  14.    Koerner, R.M. and Daniel, D.E.  1992.  Better cover-ups.  Civil Engineering, pp. 55-
         '57.        .'  '                     .                   ..
  15,    Laine,  D.L.  and Miklas Jr., M.P.   1989.  Detection and location  of leaks  in
          geomembrane liners using an electrical method: case histories. Proceed, of the 10th
          National (Superfund) Conference, Washington D.C., pp. 35-40.

  16.    Manassero, M. and Pasqualini, E.  1992.  Ground pollutant containment barriers.
          Proceed, of the Mediterranean Conf. on Environmental  Geotechnology, Cesme,
          Turkey, pp. 195-204.
  17.    May, J.H., Larson, R.J., Malone, P.O. and Boa, J.A.  1985.  Evaluation of chemical
          grout injection techniques for hazardous waste containment.  Proc.  of the  llth
          Annual Research Symp., Cincinnati, Ohio, pp. 8-18.
  18.    Millet, R.A. and Perez,  J.  1981.  Current USA practice:  slurry wall specifications.
          Journal of Geotechriical Engineering Division, ASCE, Vol.  107, No. GT8, pp. 1041-
          1056.                                   ;
  19.    Morgenstern, N. and Amir-Tahmasseb,  I.  1965.  The stability of a slurry trench in
          cohesibnless soils. Geotechnique, Vol. 15, pp. 387-395.
 20.    Mott, H.V. and Weber Jr., WJ. 1991.  Diffusion of organic contaminants through soil-
          bentonite cut-off barriers. Research Journ. WPCF, Vol. 63, No. 2, pp. 166-176.
 2.1. .   Mott, H.V., and Weber  Jr., W.J.  1992.,  Sorption of low molecular weight organic
          contaminants  by fly  ash: considerations for the enhancement  of cutoff barrier
          performance.  Environmental Science and Technology, Vol. 26,  No.  6, pp. 1234-
          1242.             .         -  .
 22.    Ran, C. and Daemen, J.J.K. 1992. Fracture grouting with bentonite  slurries.  Proc. of
          ASCE Conference on  Grouting, Soil .Improvement and Geosynthetics, Vol. 1, New
          Orleans, Louisiana, pp. 360-371.
 23.    Richardson, G.N. and  Koerner, R.M;   1989.   Geosynthetic design  guidance for
         hazardous waste landfill cells and surface impoundments.  Geosynthetic Research
         Institute, Drcxel University, Philadelphia, Pennsylvania.
 24.    Shakelford, C.D.  1992.  Performance-based design of soil  liners.  Proceed, of the
         Mediterranean Conf. on Environmental Geotechnology, Cesme,  Turkey,  pp. 145-
         -153;.    .    -        -.   :  _    •        ,-'/.-• ...,.•        ..       ..
-25.    USAGE.' 1973;  Chemical grouting.  Engineer Manual EM 1110-2-3504. U.S. Army ,
         Corps of Engineers, Department of the Army; Washington D.C.
 26. .   USAGE: 1984; Grouting technology.  Engineer Manual EM 1110-2-3506  U.S. Array
         Corps of Engineers, Department of the Army, Washington D.C.                 ;

 27.    U.S. EPA. 1982.   Hydrologic simulation on solid waste disposal sites.  SW-868.'
         Office of Solid Waste and Emergency Response; U.S.. Environmental Protection
         Agency, Washington D.C.        .
 28.    U.S. EPA. 1983.  Synthetic cap and liner systems. Draft Technical Report  Office of
     •  ... Solid Waste, U:S. Environmental Protection Agency, Washington D.C.

-------
                                                                                                      1
I
1
1
i
1
I:
1
•*
t
 I
4
ft
29.   U.S. EPA.  1984a.  Procedures for modeling flow through clay liners to determine
         required liner thickness. Draft Technical Resource Document EP A/530-SW-84-
         001.  Office of Solid Waste, U.S. Environmental Protection Agency, Washington
         D.C
30.   U.S. EPA. 1984b. Slurry trench construction for pollution migration control.  EPA-
         540/2-84-001.  Office of Emergency and Remedial Response/ U.S. Environmental
         Protection Agency, Washington D.C.

31.   U.S. EPA.  1984c.  Procedures for modeling flow through clay liners to determine
         required liner thickness.  Technical Resource Document EPA/5 30-SW-84-011,
         Office of Solid Waste, U.S. Environmental Protection Agency, Washington D.C.

32.   U.S. EPA. 1984d. Slurry trench construction for pollution migration control.  EPA-
         540/2-84-001.  Office of Emergency, and Remedial Response, U.S. Environmental
         Protection Agency, Washington D.C.
33.   U.S. EPA.  1985a.  Covers for uncontrolled hazardous  waste sites.  EPA/540/2-
         85/002.  Hazardous Waste Engineering Research Laboratory, U.S. Environmental
         Protection Agency, Cincinnati, Ohio.
34.  . U.S. EPA.. 1985b.  Leachate plume management  EPA/540/2-85/004.  Office of Solid
         Waste  and Emergency Response,  U.S. Environmental Protection  Agency,
         Washington D.C.
35.   U.S. EPA.   1989a.   Final  covers on hazardous waste  landfills  arid surface
         impoundments.  Technical Guidance Document EPA/530-SW-89-047.  Office of
         Solid Waste and Emergency Response, U.S. Environmental Protection Agency,
         Washington D.C.
36.   U.S. EPA. 1989b.  Requirements for hazardous waste landfill design, construction,
         and closure.  Seminar Publication EPA/625/4-89/022.  Center for Environmental
         Research Information, U.S.-Environmental Protection Agency, Cincinnati, Ohio,
37.'   Van Impe, W.F.   1989; Soil  improvement  techniques and  their  evolution.. A.A.
         Balkema Publishers, Rotterdam, The Netherlands.
38;   Weaver, K.D., Coad, R.M., and Mclntosh, K.R. 1992. Grouting for hazardous waste
         site remediation at  Necco  Park, Niagara Falls; New York.   Proc.  of ASCE
         Conference ow Grouting, Soil Improvement  and Geosynthetics,  Vol.  2, New
         Orleans, Louisiana, pp.  1332-1343.

39.   Zimnuef*T.F.; LaPlante, CM: and Branson,  D.  199,2.  The effects of freezing  and
      .   thawing on the permeability of compacted clay landfill covers and liners. Proceed, of
         th&vMediterranean Conf. on Environmental Geotechnology,  Cesme, Turkey, pp.
                                                     29

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