EPA/530-SW-85-014
                          DRAFT



               Minimum Technology  Guidance


                            on


                   Double Liner Systems


                           for


           Landfills and Surface Impoundments--


           Design, Construction, and  Operation
                Protection
                          V_f — • • "~ J
00          - j                            Second version
^30 South  Dearborn Street
Chicago, Illinois  60604                          MaY 24,1985

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                                    II
                      Minimum Technology Guidance  on
                         Double  Liner Systems  for
                    Landfills and Surface Impoundments

                            TABLE .OF CONTENTS

                                                              PAGE

   INTRODUCTION ---------------_______  m

   FML/COMPOSITE DOUBLE LINER SYSTEM ----------  -   l

   I.  Primary Leachate Collection  and  Removal  Systems  - - -  4
       for Landfills

        A.  Guidance  --------------------  4

        B.  Discussion -------------------  5

  II.  Double Liner Specifications  -------------  n

        A.  Guidance  --------------------  n

        B.  Discussion -------------------  26

 III.   Secondary Leachate Collection Systems Between - - -   43
        the Liners

        A.  Guidance  --------------------  43

        B.  Discussion -------------------  45

  IV.  Construction Quality Assurance -----------   50

        A.  Guidance --------------------  50

        B.  Discussion -------------------  52

   FML/LOW PERMEABILITY SOIL DOUBLE LINER SYSTEM ------  56

   References  ------------------------ 53

   Suggested Reading List ------------------71
U.S. Environmental Protection Agency

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                                      Ill
                                  Introduction






      On November 8,  1984,  the President signed into law the Hazardous and



 Solid Waste Amendments of  1984 (H5WA).   Under Sections  3004(o) and  3015 of



 the HSWA certain landfills and surface  impoundments are required to have



 "two or more liners  and a  leachate collection system above  (in the  case of a



 landfill) and between such liners," unless the conditions for a statutory



 variance are met.  Section 3004(o)(5)(B) allows the use of a particular



 type of liner design pending the issuance of EPA regulations or guidance



 documents (through the notice and cement process)  inplementing the double



 liner requirement  in Section 3004(o).   This guidance document is intended to



 provide guidance on  designs in addition to the design set out in Section



 3004(o)(5)(B)  that the Agency believes  meet the requirements of §§3004(o)



 and 3015 of  the HSWA. and are protective of human health and the environment.



 This document  identifies tvro such double liner systems.



      The first double liner system includes a top liner and a composite bottom



 liner (Figures 1 & 2).   The top liner is designed,  operated, and constructed



 of  materials to prevent the migration of any hazardous  constituents into



 such liner during  the period the  facility remains in operation (including a



 30-year post-closure  monitoring period).   The top liner is a flexible membrane



 liner (FML), which is addressed in  this  guidance in some detail.  The bottom



 liner consists of  two components that are intended  to function as one system,



hence,  the term  "conposite"  liner.  Like the  top liner, the upper component



of the bottom  liner is  designed, operated,  and constructed to prevent the



migration of any constituent  into this component during the period  of facility



operation, including the post-closure monitoring period.  The upper conponent



of the composite liner  is also a flexible membrane  liner (EML).  The lower



conponent of the bottom liner is designed, operated, and constructed to

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                                                             FIGURE 1
                                      SCHEMATIC OF AN FML/COMPOSITE DOUBLE LINER SYSTEM
                                                         FOR A LANDFILL
           Protective
          Soil or Cover
           (optional)
Primary Leachate
 Collection and
Removal System
       Secondary Leachate
         Collection and
         Removal System
                                                                                                         Top Liner
                                                                                                          (FML»
                                                               Bottom Composite
                                                                     Liner
                                         vovS o  '^   °  °   °  ' ° 'Oiv? O  . Q o:
                                            OC.      Solid Waste    2* ft-
                                                       "
                                         i M i n M 1 1 M 1 1 1 ii ii 1 1 1
                                               _S
                                              (^Drainage Material
                                              ^Drainage Material
                                                          Low Permeability Soil
Native Soil Foundation
                                                            Upper Component
                                                                 (FML)
Lower Component
 (compacted soil)
                                                                                                                       (Not to Scale)

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                                                               FIGURE 2
                                       SCHEMATIC OF AN FML/COMPOSITE DOUBLE LINER SYSTEM
                                                    FOR A SURFACE IMPOUNDMENT
    Protective
   Soil or Cover
    (optional)
Secondary Leachate
  Collection and
  Removal System
                                                                                                  Top Liner
                                                                                                    (FML)
                                                           Low Permeability Soil
                                                           Native Soil Foundation
           Bottom Composite
                Liner
 ;;j;:::'   Upper Component
             (FML)
Lower Component
 (compacted soil)
Note:   Primary leachate collection system not used in surface impoundment.
            (Not to Scale)

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                                       VI
 minimize the migration of any constituent through the upper conponent if a



 breach in the upper conponent were to occur prior to the end of facility



 operation, including the post-closure monitoring period.  The lower  conponent



 of the composite bottom liner is a conpacted soil that should meet tecnivLcal



 requirements set forth in this document.



      The second design includes the performance standard from Section 3004(o)(5)(B)



 This double liner system includes a top liner designed,  constructed,  and



 operated of materials to prevent the migration of any constituent into such



 liner during the period the facility remains in operation (including a 30-year



 post-closure monitoring period),  and a lower liner designed,  operated, and



 constructed to prevent the migration of any constituent  through the  liner



 during this period (Figures 3  & 4).   The  top liner in this  design is  an  FML



 and the bottom liner  is a conpacted low permeability soil.   Section  3004(o)(5)(B)



 provides  that a three-foot tluck liner of recompacted clay  or other  natural



 material will satisfy the lower liner requirement.   Because EPA believes



 that  three feet of clay or other natural  material  will not  prevent migration



 in  most cases,  this document provides  guidance  on  what the  Agency believes



 is  an adequate  lower  liner.  The Agency interprets the term "natural  material"



 to  mean any naturally occurring soil that can be compacted, without man  made



 additives,  into a  liner with a permeability of  1 X 10~7cm/sec or less.



     Although both of these double  liner  system designs  are acceptable,  this



 guidance contains more  information  en  the first design than the second.  The



 second design is more dependent on  site specific characteristics, such as  the



amount of annual rainfall,  than the  first design.  Also, the  second design



requires a series of assumptions on  leakage  rates, flow  characteristics, and



other factors.  Therefore, the specificity of guidance that is  given  en  the



second double liner system design is more limited.

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                                                              FIGURE 3
                                   SCHEMATIC OF AN FML/COMPACTEO SOIL DOUBLE LINER SYSTEM
                                                          FOR A LANDFILL
         Protective
        Soil or Cover
         (optional)
                                            Top Liner
                                             (FMU
                                                  Drainage Material O"**~  <*»***
Primary Leachate
 Collection and
 Removal System
        Secondary Leachate
          Collection and
          Removal System
    Thick Layer *
Low Permeability Soil
                                                             Native Soil Foundation
                                                            Bottom Liner
                                                           (compacted soil)
« Thickness to be determined by break through time.
                                                                                                                        (Not to Scale)

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         Protective
       Soil or Cover
         (optional)
 Secondary Leachage
    Collection and
   Removal System
                                                                 FIGURE 4
                                       SCHEMATIC OF AN FML/COMPACTED SOIL DOUBLE LINER SYSTEM
                                                       FOR A SURFACE IMPOUNDMENT
                                                                                                   Top Liner
                                                                                                     (FML)
                                                                 Thick Layer *
                                                             Low Permeability Soil
                                                            Native Soil Foundation
 Bottom Liner
(compacted soil)
•Thickness to be determined by breakthrough time.
Note:   Primary leachate collection system not used
        in surface impoundment.
(Not to Scale)

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                                       LX
      The double liner system set out in Section 3004(o)(5)(B)  and the two



 double liner systems discussed in this guidance are not  the  oily double



 liner systems that may be used to comply with the minimum technology requirements



 of HSWA.  Other double liner systems,  depending on their design,  operation,



 location,  and waste types to be received, may be acceptable.   Alternative



 double liner systems may include other amended soil materials  with man made



 products or natural materials such as  soil cement,  lime/soil mixture, or fly



 ash/soil mixture.   However,  an owner/opera tor choosing to install an alternative



 double liner system should confer with the Agency during the design and



 construction of the system in order for EPA to ascertain whether the system



 will meet the minimum technology requirements of HSWA.



      For example,  an owner/operator of an interim status landfill or surface



 impoundment who wants to install one of the two double liner systems described



 in this  guidance below the ground-water table should request review of the



 design plans prior to construction.  Liner and leachate  collection system



 installation below the ground-water table involves  many  site-specific



 considerations.  Such systems are not  specifically  discussed in  this guidance.



 Owners and operators choosing the design in §3004(o) (5) (3) or  one of the two



 designs  that are discussed in this guidance (particularly the  FML/composite



 design)  should be  able to proceed with construction with substantially less



 Agency interaction.   (This is likely to be  the case for  both interim status



 and permitted units.)



     This  guidance  is  intended to incorporate the current state-of-the-art



 regarding  the design,  construction,  and operation of hazardous waste land



 disposal units.  The  attempt  has been  made  to include an element  of practicality



 in specifying how to construct  a unit.   However,  this guidance does not address



all components of  facility design, construction,  operation, and  closure.  Por




example,  it does not address the  final  cover  requirements for  landfills and

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                                      X
certain surface impoundments, nor does it discuss considerations for freeboard



in inpoundment design and operation.  The Agency's previously issued guidance



(July 1982) continues to be applicable in these areas.  [NOTE:  EPA does



not believe §§264.228(a)(2)(iii)(E) or 264.310(a)(5) for permitted units



require the installation of two EMLs in the final cover when two EMLs are



used in the double liner system.  A single FML in the final cover that is



equivalent to the thicker FML used in the double liner system will be



considered to have an equivalent permeability. ]



     This guidance is one step in the Agency's efforts to imp lenient the



mininum technology requirements of §§3004(o) and 3015 of the HSWA.  We expect



to formalize many of these guidelines in the future by incorporating them



into the Agency's regulations.

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                       FML/COMPOSITE DOUBLE LINER SYSTEM





      The FML/conposite double liner system consists,  at a mininum,  of a



 primary leachate collection and removal system (for landfills),  a top FML



 liner, a secondary leachate collection system,  and a  bottom composite FML/low



 permeability soil liner.  A detailed cross section of the basic  conponents



 of the FML/conposite double liner system for landfill and surface impoundment



 units is shown in Figure 5.  The function of the primary leachate collection



 and removal system at landfills is to minimize the head (depth)  of leachate



 on the top liner during operation and to remove liquids through  the post-closure



 monitoring period.   The leachate collection and removal system should be



 capable of maintaining a leachate head of less  than 1-foot.   The top  liner



 should be designed,  constructed,  operated,  and  maintained to prevent  migration



 of waste liquid constituents during operation (including the post-closure



 monitoring period)  and should allow no more than de minimis  infiltration  of



 any constituent into the liner itself.   The secondary leachate collection



 system between the  two liners should be designed,  constructed, operated,



 monitored,  and maintained to rapidly detect,  cc^lect,  and remove liquids



 entering the  collection system for treatment  through  the post-closure monitoring



 period.  The bottom liner consists of tv*o components  that are intended to



 function as one system,  hence,  the term "composite" liner.   Like the  top



 liner, the upper conponent of the  bottom liner  should be designed,  operated,



 and constructed to prevent the migration of any constituent  of the  waste



 liquid into the upper component during  the period of  facility operation,




 including the post-closure monitoring period.   For design purposes, the



post-closure monitoring period should nominally be assumed to be 30 years.



The lower component of the bottom  liner should  be designed,  operated,  and




constructed to minimize the migration of any constituent of the  waste liquid

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                  Materials
                  FIGURES
  SCHEMATIC PROFILE OF AN FML/COMPOSITE
   DOUBLE LINER SYSTEM FOR A LANDFILL
           Dimensions and Specifications
                                                                                                                  Nomenclature
Graded Granular Filter Medium
Granular Drain Material
   (bedding)


Flexible Membrane Liner (FML)

Granular Drain Material
   (bedding)


Flexible Membrane Liner (FML)
Low Permeability Soil, Compacted in Lifts
   (soil liner material)
   Note:   FML thickness > 45 mils
   recommended if liner is not
   covered within 3 months.
                                                   A   •
                                                   % °K       v.-
                                                   ''''
    Recommended Thickness > 6 in.
    Maximum Head on Top Liner = 12 in.
    Recommended Thickness 2* 12 in.
    Hydraulic Conductivity > IxlO'2 cm/sec
V—Recommended Thickness of FML >30 mils
       (see note)
    Recommened Thickness > 12 in.
    Hydraulic Conductivity > IxlO"2 cm/sec
     	Drain Pipe	—	
   - Recommended Thickness of FML > 30 mils
       (see note)

    Recommended Thickness > 36 in.
    Recommended Hydraulic Conductivity < IxlO'7
       cm/sec
                                                       Prepared in 6 in. Lifts
                                                       Surface Scarified Between Lifts
                Unsaturated Zone
                                                       Groundwater Level
                                                                    Saturated Zone
                                                          W////////////M
                                                        Sol id Waste
Filter Medium
Primary Leachate Collection and
   Removal System

Top Liner (FML)

Secondary Leachate Collection and
   Removal System
                                                                                                           Compression Connection (contact)
                                                                                                             Between Soil and FML
Bottom Liner (composite FML and
  compacted low permeability soil)
                                                                                                           Native Soil Foundation/Subbase
                                       po

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through the upper component if a breach in the upper component were to occur



prior to the end of facility operation, including the post-closure monitoring



period.  Compacted low permeability soil is reconirended for the lower conponent.



EPA believes that this design is effective in protecting human health and the



environment because the combination of the twD components in the bottom liner



system provides for virtually complete removal of waste or leachate by the



leachate collection system if a leak were to occur in the top liner.

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       I.   Primary Leachate Collection  and Renoval Systems for Landfills

                                    Contents

                                                               Page

      A.   Guidance  -----  	 __________ 	 _       4

           Objective	        4
           Design specifications -------------        4
           Construction specifications  -  	        5
           Operation specifications	        6
     B.   Discussion
    A.  Guidance

     Overall Design, Construction, and Operation Objective

     The primary  leachate collection and removal system system should be

designed to ensure that the leachate depth above the top liner does not

exceed one foot;  be constructed of materials that can withstand the chemical

attack that results from waste liquids or leachates; be designed and constructed

so  as to withstand the stresses and disturbance from overlying wastes,

waste cover materials, and equipment operation; be designed and operated to

function without  clogging through the post-closure monitoring period; and be

operated to collect and remove leachate through the post-closure monitoring

period.  Components should be properly installed to assure that the specified

performance of the leachate collection system is achieved.

     Design

     The primary  leachate collection and removal system should have:

     (a) At least a 30 centimeter (12 inch) thick granular drainage layer

that is chemically resistant to the waste and leachate, with a hydraulic

conductivity not  less than 1 x 10~2 cm/sec and with a minimum bottom slope

of 2 percent.

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 Innovative leachate collection systems  incorporating synthetic drainage



 layers or nets may be used if  they are  shown  to  be  equivalent to or more



 effective than the granular design,  including chemical compatibility,



 flow under load,  and protection of the  FML  (e.g., from puncture).



      (b)  A graded granular or  synthetic fabric filter above the drainage



 layer to prevent  clogging.  Criteria for graded  granular filters and for



 synthetic fabric  filters  are found in numerous publications such as the



 Geotextile Engineering Manual  available fron  the Federal Highway Administration



 and others.   The  granular drainage material should  be washed to remove fines



 before  installat ion.



      (c)  A drainage system of  appropriate pipe size and spacing on the bottom



 of  the  unit  to efficiently collect leachate.  These pipe materials should be



 chemically resistant  to the waste  and leachate.  The piping system should be



 strong  enough to  withstand the weight of the  waste  materials and vehicular



 traffic placed on or operated  on top  of it.



      (d)  A primary leachate collection  system that  covers the bottom and



 sidewalls of  the  unit.



      (e)  A sump in each unit or cell  should be capable of automatic and



 continuous functioning.  The sump  should contain a  conveyance system for the



 removal of leachate fron the unit  such  as either a  sump pump and conveyance



 pipe or gravity drains.



      (f) A written construction quality assurance (CQA)  plan prepared by the



owner/operator to be used during construction of the double liner system



 including  the primary  leachate collection and removal system.  See Section



IV, "Construction Quality Assurance", for specific details.



     Construction



     (a) The owner/operator should use the construction quality assurance

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 plan to monitor and  document  the quality of materials used and the conditions



 and manner of their  placement during construction of the primary leachate



 collection and removal  system.  See Section IV, "Construction Quality Assurance",



 for specific details.



      (b)  The documentation  for the CQA program should be kept on-site in the



 facility operating record maintained for the landfill unit.








     Operation



     The  following operational procedures should be followed:



     (a)  The leachate removal system should operate automatically whenever



 leachate  is  present  in  the  sump and should remove accumulated leachate at



 the earliest practicable time to minimize the leachate head on the liner



 (not to exceed 12 inches);



     (b)  Inspect weekly and after major storm events for proper functioning



 of the leachate collection  and removal system, and for the presence of leachate



 in the removal sump.  The owner or operator should keep records on the system



 to provide sufficient information that the primary leachate collection system



 is  functional  and operated properly.  We recommend the amount of leachate



 collected be  recorded in the facility operating record for each unit on a



 weekly basis?



     (c) Cleaning out of collection lines periodically; and



     (d) A storage permit for collected leachate, if required.  Collected



 leachate  is  subject to the prohibition on placement of liquids in landfills




 in RCRA §3004(c).



     B.  Discussion



     The Agency believes that practical designs for leachate collection and




 removal systems can maintain a leachate depth of one foot or less, except



perhaps temporarily (for a few days) after major storms.  The specifications

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 presented here, judiciously applied,  are expected to accomplish that requirement.



      The minimum thickness (30 centimeters or 12 inches)  of the drainage



 layer allows sufficient cross sectional area for transport of drainage leachate.



 The two-percent minimum slope is also intended to promote drainage.   In most



 cases, the Agency believes thicker drainage layers and greater slopes will



 be selected by owners and operators to maximize the efficiency of  the leachate



 collection and removal system.   The hydraulic conductivity of not  less than



 1 X 10~2 on/sec was chosen because materials widely used  as drainage media



 are coarse enough tiiat their hydraulic conductivities are estimated  to be



 1 X 10~2 cm/sec or greater.



      It is not clear if the statutory requirements of §3004(o)(l)(A)(i)  require



 the primary leachate collection system to  be on the sidewalls of a landfill.



 The current Part 264 requirements in  §264.301(2)  require  a collection and



 removal system immediately above the  liner to collect and remove leachate.



 The previous liner guidance  dated July,  1982,  did not specify whether the



 leachate collection system was only to cover the bottom or also the  sidewalls



 of the  unit.  The  Permit Writer's Guidance Mani-ul for Hazardous Waste Land



 Treatment,  Storage,  and Disposal Facilities, October  1983,  indicates  that



 the need for a  leachate collection system  of the  sidewalls of a landfill



 should  be based on site-specific  conditions  of expected leachate flow over



 the life  of the facility.  Generally,  we feiuourage the installation of a



primary leachate collection system on both the base and sidewalls of  double



 liner systems under  §3004(o)(1)(A)(i).  The  two designs in this  guidance



recommend leachate collection on the sidewalls because it  allows leachate  to



drain to the sump  faster and minimize ponding of  leachate  within the waste



on the sidewalls of the top liner.

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                                      8
      The  following  is  a list of factors that affect liquid transmission in

 the leachate collection system drain layer:
      0  Inpingenent rate of  liquid on the collection drain layer;
      0  Slope of the drain layer;
      0  Diameter and spacing between the drainage pipes;
      8  Coefficient of hydraulic conductivity of the saturated sand or
        gravel  drain layer;  and
      0  Cleanliness (lack of fines) of the sand or gravel.

A method  for estimating quantity of liquids collected and liquid depth above

the  liner is presented in Landfill and Surface Impoundment Performance Evaluation,

SW-869, April  1983 (EPA 83).

      Drain pipe diameter and spacing are ittportant because they affect the

head that builds up on the  top liner between pipes.  The closer the pipes

are  together,  the less the head.  Also, the pipe diameter should be large

enough to efficiently carry off the collected leachate.  Since the philosophy

for  all aspects of liner design is to minimize liquid transmission through

the  liner system, the head  on the liner should be miaunized.  But the spacing

and  size  of the drainage piping system necessary to acconplish this depends

on other  characteristics of the drainage layer (e.g., hydraulic conductivity)

and  on the inpingement rate of liquids, which is a function of precipitation

and  the effectiveness of the cover system.  The Agency is, therefore, not

specifying minimum spacing or pipe diameter in this guidance.  However, EPA

believes  that designs incorporating 6-inch diameter perforated or slotted

pipes spaced 50 to 200 feet (15 to 60 meters) apart will effectively minimize

head on the liner system in most cases.  Information on leachate collection

is presented in Appendix V of Lining of Waste Impoundment and Disposal Facilities,

SW-870, March 1983 (EPA 83A).  The owner or operator should demonstrate

through appropriate design  calculations that the maxinum recommended one-foot

head will not be exceeded.

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     The leachate collecticn and removal system should be overlain by a

 graded  granular filter or synthetic fabric filter.  The purpose of tliis is

 to prevent clogging of the voids in the drain layer by infiltration of fines

 from the waste.  If a granular filter is used, it is inportant that the

 relationship of grain sizes of the filter medium and the drainage layer be

 appropriate if the filter is to fulfill its function to prevent clogging of

 the  drainage layer and not contribute to clogging.  Criteria for graded

 granular filters and for synthetic fabric filters are found in numerous

 sources  such as:

 Graded granular filters:

     - Earth Manual.  1984.  Bureau of Reclamation, U.S. Department of the
       Interior.  Government Printing Office, Washington, DC.

 Geotextiles:

     - Koerner, Robert M., and J.P. Welsh.  1980.  Construction and Geotechnical
       Engineering Using Synthetic Fabrics.  John Wiley and Sons, New York.

     - Horz, R.C. 1984.  Geotextiles for Drainage and Erosion Control at
       Hazardous Waste Landfills.  EPA Interagency Agreement No.  AD-96-F-1-400-L.
       U.S. EPA, Cincinnati, Ohio.

     - Geotextile Engineering Manual, Training \anual,  Federal Highway Administratio

     Innovative leachate collection systems that are equivalent to, or more

 effective than, the granular system described above may be used.  These

 innovative systems such as plastic nets can be very thin, on the order of

one-inch thick, and have the drainage capacity of a sand layer one-foot

thick.   These systems should be capable of maintaining a leachate head of one

foot or less.   The following criteria should be addressed for determining

equivalence:

     0  Design - hydraulic transmissivity (i.e., the amount of liquid that
                can be removed)

              - compressibility (i.e.,  ability to withstand expected overburden
                pressures while remaining functional)

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                                      10
              - conpatibility (chemical)  with waste liquid

              - conpatibility (mechanical)  with the EML (i.e., will not
                deform the EML under the  expected overburden)

              - slope stability

     0 Construction - Construction characteristics (i.e., ease of construction)

     0 Operation/performance characteristics

            - drainage or flow characteristics (i.e. how fast liquids will
              flow and what volume will flow)

            - tine required to return the leachate head to one foot or less
              after a rainfall event

            - material creep

            - useful life of system

            - ability to resist clogging

            - ability to verify performance.

     An owner or operator wishing to use  a leachate collection system other than

the recommended one should compare the properties of his design against the

recatmended design using the above criteria.  If equivalent, or better he

should proceed; if not, he should abandon the alternate design.  If one or

nore of the factors is not equivalent, the collection  system will probably

not perform well,  and will potentially become a source of constant trouble

to its owner/operator.

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                                       11
                        II.  Double Liner Specifications

                                    Contents

                                                             Page

      A.  Guidance	    11

           Objective	     11
           Design	     12
                a.  EML top liner	________ —     12
                b.  Gonposite bottom liner	      17

           Construction		_     19 -
                a.  FML	     19
                b.  Low permeability soil	______     20

            Operation	___	     26

      B.  Discussion	______      26
     A.  Guidance

     Overall Design, Construction, and Operation Objective

     All new surface impoundments and landfills, new units, lateral expansions,

and replacement units must have two  liners.  The two liners nust be designed,

constructed, and operated to protect human heal'-h and the environment.  The

top liner should be designed, operated, and constructed of materials to

prevent the migration of any waste liquid constituents into such liner during

the period the unit remains in operation (including any post-closure monitoring

period), and should allow no more than de minimis infiltration of waste

constituents into the liner itself.  The top liner discussed herein is a

flexible membrane liner (FML).  The secondary leachate collection system is

between the two liners.   The bottom liner consists of tvro components that

are intended to function as one system,  hence,  the term "composite" liner.

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                                       12
 Like the top liner, the upper component of the bottom liner should be designed,



 constructed, and operated to prevent the migration of any constituents into



 this conponent during the period of facility operation,  including any post-closure



 monitoring period.  The upper compcnent of the bottom liner of this design



 is also an EML.  The lower conponent of the bottom liner should be designed,



 constructed, and operated to minimize the migration of any constituent through



 the upper conponent if a breach in the upper conponent were to occur prior



 to the end of unit operation,  including the post-closure monitoring period.



 The lower conponent of the bottom liner is a conpacted low permeability soil



 material.   All liner materials should be resistant to the waste liquid



 constituents the liner will encounter,  and be of  sufficient strength and



 thickness to withstand the forces  it will encounter during construction and



 operation.   Foundation preparation is recontnended to ensure that the structural



 stability of the subgrade is sufficient to support the liners without damaging



 them and to prevent failure due to pressure gradients (including mechanical,



 gas, and liquid static and external hydrogeologic forces).   The double liner



 system should cover all areas  likely to be exposed to waste and leachate.








     Design



     0 This  liner system  should be constructed conpletely above the seasonal



high water  table (i.e., in unsaturated  soil).



     0 The  two  liners  should consist  of the following, as  a minirtum:



     (a) An FML top  liner;



     (1) The EML top liner  should  be  at  least a 30 mils  thick;  however,  if



the liner is to be exposed  to the weather  for an  extended period before it



is covered by a protective  soil  layer or the  waste,  or if  the  liner is to  be



operated without a protective cover,  it  should be at least  45 mils  in thickness.

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                                       13
 Many units will require a thicker liner to prevent failure while the unit  is



 operating, including any post-closure monitoring period.   The adequacy of



 the selected thickness should be demonstrated by an evaluation considering



 the type of FML material and site-specific factors such as:  expected operating



 period of the landfill or surface impoundment unit, pressure gradients,



 physical contact with the waste and leachate, climatic  conditions (environmental



 factors), the stress of installation,  and the stress of daily operation



 (e.g.,  placing wastes in the landfill or sludge removal in surface impoundments),



 Stresses tend to be higher for surface impoundment units  than for landfill



 units.   Several factors can increase  liner stresses in  surface impoundments



 such as: (1)  cleaning or maintenance  activities;  (2) thermal stress;  (3)



 hydrostatic pressure (head and wave action);  (4)  abrasion;  (5)  weather exposure



 (ultraviolet  light,  oxygen,  ozone,  heat,  and  wind);  and (6)  operating conditions



 (inlet  and  outlet  flow,  active life, exposure to  animals,  treatment  processes).



 Because of  these factors,  uncovered surface impoundments generally require



 thicker liners  than the  45-mil minimum.   Thicknesses of 60-100 mils  have been



 necessary in  some  applications.  A  protective l~yer covering the liner in



 surface impoundments can reduce  the stresses on the liner.   The Agency will



 consider appropriate historical data and  actual test data regarding  the



 performance of  liner materials of the designed thickness as  part of  the



 evaluation of the permit application.



     (2)  Liners should  be chemically resistant to  the  waste and  leachate



managed at the unit.  The Agency strongly prefers test data  because  the



demonstration of chemical resistance should be based on representative waste



effects.  The EPA Test Method 9090  (October 1, 1984, proposal or revised



editions) or an Aqercy approved equivalent test method should be used  to



test chemical  resistance of liners.  Complete copies of the  text of  sampling

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                                      14
 and analytical methodologies addressed in the October 1,  1984,  proposed

 rules  (including nethod 9090) are available from the National Technical

 Information Service  (NTIS), 5285 Port.Royal Road, Springfield,  Virginia

 22161,  (703) 487-4650. The document number is PB-85-103-026.  In judging

 chemical compatibility of wastes and membranes, the Agency will consider

 appropriate historical data or actual test data if obtained under longer or

 more severe test conditions.

     (3) The National Sanitation Foundation (NSF) presents liner material

 properties  and factory seam requirements in their Standard Number 54 for

 Flexible Membrane Liners, November 1983.  The Agency suggests that material

 and  seam specifications such as those in the National Sanitation Foundation

 standard be used to assure material quality from the liner manufacturer.

 Liner materials listed by the National Sanitation Foundation for industrial

 service, or liner materials that are not listed but consistently meet the

 specifications of the NSF Standard 54, are acceptable for assuring quality

 from the manufacturer.  Test methods used to establish these requirements

 should comply with applicable American Society of Testing and Materials

 (ASTM)  procedures,  recommended methods in EPA document SW-870 Lining of

Waste Impoundment and Disposal Facilities (tables VIII-1 to 7)  (EPA 1983A),

or an equivalent method when available.  The FMLs covered by NSF standard

 54 include at least the following:

     0  Polyvinyl Chloride (PVC)
     0  Polyvinyl Chloride Oil Resistant (PVC-OR)
     8  Chlorinated Polyethylene (CPE)
     0  Butyl Rubber (IIR)
     0  Polychloroprene (CR)
     0  High Density Polyethylene (HOPE)
     0  Ethylene-Propylene Diene Terpolymer (EPDM)
     0  Epichlorohydrin Polymers (CD)
     0  Polyethylene Ethylene Propylene Alloy (PE-EP-A)

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                                       15
        High Density Polyethylene Elastomeric Alloy (HDPE-A)

        Chlorosulfonated Polyethylene (CSPE)
        Chlorosulfonated Polyethylene,  Low Vfeter Absorption (CSPE-LW)
        Thermoplastic Nitrile - PVC (TN-PVC)
        Thermoplastic EPDM (T-EPDM)
        Ethylene Interpolymer AlJoy (EIA)
        Chlorinated Polyethylene Alloy (CPE-A)

 The address for the National Sanitation Foundation is:

                    3475 Plymouth Road
                    P.O. Box 1468
                    Ann Arbor,  Michigan 48106 USA

      (4)  ETMLs  should be free of pinholes,  blisters, holes, and contaminants,

 which include,  but are not limited to,  wood, paper, metal, and nondispersed

 ingredients.

      (5)  The compounding ingredients  used  in producing FMLs  should  be  first

 quality,  virgin materials providing durable  and effective  formulations for

 liner applications.   Clean rework materials  containing encapsulated scrim or

 other fibrous materials should not be  used in the  manufacture of flexible

 membrane  liners (FML)  used for hazardous waste  containment.  Clean  rework

 materials of the same  virgin ingredients generated from the manufacturer's

 own production  may be  used by  the  same manufacturer, provided that  the finished

 products  meet the  material specification requirements.

      (6)  EMLs in landfill units, and in units with the minimum recommended

 thickness, should be protected from damage from above and below the membrane

by a least 30 centimeters  (12  inches) nominal, 25  centimeters (10 inches)

minimum, bedding material  (no  coarser than Unified Soil Classification System

 (USCS) sand (SP) with 100 percent of the washed, rounded sand passing the

1/4 inch sieve) that is free of rock, fractured stone, debris, cobbles,

rubbish, and roots, unless it  is known that the FML material is not physically

impaired by the material under load.  The surface of a completed substrate

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                                       16
 should be properly compacted,  smooth,  uniform,  and  free  from  sudden changes

 in grade.  The secondary leachate collection system or the low permeability

 soil may serve as bedding materials when in direct  contact with EMLs if they

 meet the requirements specified herein.   Polymeric  materials  such as geotextiles

 and synthetic drainage layers  may also serve as bedding materials when in

 direct contact with either surface of  the top IML or with the upper surface

 of the FML component of the bottom liner,  if they provide equivalent protection.

 In determining equivalent protection given by geotextile or other specific

 materials,  the Agency will consider historical  data and actual test data

 that relate to site-specific conditions.   To demonstrate that a synthetic

 drainage layer can serve as bedding material, it should be shown that the

 synthetic drainage layer does  not exhibit brittle failure under overburden

 stresses and stresses caused by equipment used  for  construction or waste

 placement.

      Note:   In most cases an FML  should not be  in contact with native, in situ soil.

      Note:   Light  geotextile bedding material may require an additional
             precaution  if the  slopes are  exposed to high velocity winds.

     '(7)  For surface impoundment and  landfill  units in which the sidewalls

will be  uncovered  and exposed  for extended periods  before wastes are placed,

the  design of  the  bedding material  used below the top liner should be highly

permeable and  include gas  venting if the potential  for gas generation under

the bottom liner exists,  or if the  slopes  of a  surface impoundment will be

exposed  to high velocity winds.

      (8)  Penetration of a liner  by any designed means should be avoided.

Where structures are necessary, such as:

      0 Pipes  (both horizontal and  vertical),
      0 Vertical support columns,
      0 Inlets, outlets,
      0 Sumps, and
      0 Divider walls,

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                                       17
 it is essential to obtain a secure,  liquid-tight seal  between the  structure



 and the FML.  An FML nay be attached to a structure with a mechanical-type



 seal supplemented by chemically conpatible caulking, adhesives, or heat



 fusion to effect a liquid-tight seal.   Conpaction of areas adjacent  to the



 structure should be to the same density as the surrounding soil to minimize



 differential settlement.   Sharp edges  on the  structure should not  come in



 contact with an FML.



      (9)  Bridging or stressed conditions in  the FML should be avoided with



 proper slack allowances for shrinkage  of the  FML during installation and



 before the placement  of a protective soil layer or waste.








      (b) A composite  bottom liner;



      (1) The composite bottom liner  consists  of two ccnpcnents, an upper FML



 component and a lower corrponent of conpacted  low permeability soil.



      (2)  The upper FML component should be of at least a 30-mil membrane;



 some units will require a thicker liner to meet the site conditions without



 probable failure during construction and while the unit is operating, including



 any post-closure monitoring period.  The adequacy of the selected thickness



 should be demonstrated by an  assessment  of the type of liner material and



 site-specific factors.  The liner should be chemically  resistant to the



waste  and leachate managed at  the unit.  The EPA test method 9090 or an



equivalent test method should be used to test  chemical  resistance of liners.



In judging chemical compatibility of the membrane with  the waste to be managed,



the Agency will consider appropriate historical data and actual test data



obtained under longer or more severe test conditions.



 (3) The upper FML component of the conposite bottom liner should be protected



from damage from above by at least 30 centimeters (12  inches) of bedding

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                                       18
 material no coarser than Unified Soil Classification System (USGS) sand  (SP)



 that is free of rock, fractured stone,  debris,  cobbles,  rubbish,  and roots,



 unless it is known that the liner material under load is not physically



 inpaired by the material.   The subgrade to the  synthetic upper  conponent



 will be the uppermost lift of the conpacted lower conponent.  This lift



 should be sufficiently snoothed to provide a good bed for the overlying



 synthetic material.   The secondary leachate detection, collection, and renoval



 system serves as the top bedding material  and the low-permeable soil conponent



 of the bottom liner serves as the lower bedding material and should meet the



 requirements specified herein.   Polymeric  materials  such as  geotextiles nay



 also be used as top  bedding materials when in direct contact with the liner



 if they provide equivalent protection.   They should  not  be used as the bedding



 below the  FML,  as they would  increase the  transmit sity between  the two conponents



 of the  bottom liner.   In determining  equivalent  protection for  geotextile,



 the Agency will consider historical data and actual  test data that relates



 to site-specific conditions.



      (4) The FML upper conponent  and  the soil lower  conpcnent interface trust



 be in direct contact,  and  be  designed and  constructed to provide a compression



 connection (contact) between  the  two  coriponents  to minimize  flow between them.



 The  two components are maintained in  contact  by  the  overburden  load.  The design



 and  construction should minimize  void space,  channels, and other conditions



 promoting  lateral flow of  liquids at  this  interface.  This requirement is



 not  intended to preclude liner installers  from purposely leaving designed



 folds in the synthetic  liner material.  No fabric or other high-permeability



bedding material should be used between the upper and lower  conponents that



would have high transmissivity.  Overburden pressure exerted on the secondary



 liner from overlying materials may be sufficient to adequately  reduce the

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                                       19
 potential for lateral flow.  EPA recognizes that there may be procedures or



 materials which would further reduce the transmissivity of this interfacial



 zone and encourages demonstrations to- that effect.



      (5) The soil conpcnent of the conposite liner should be at least 90



 centimeters (36 inches) of cottpacted,  enp laced,  low permeability soil with an



 in-place saturated hydraulic conductivity of 1 X 10~^ cm/sec or less.



 The compacted material must be free of rock, fractured stone,  debris, cobbles,



 rubbish, and roots that would increase hydraulic conductivity or serve to



 promote preferential leachate flow paths.



      (6) The foundation subsoil that underlies the  compacted low permeability



 soil component should be structurally  irmobile during construction and operation



 of the  unit (including any post-closure monitoring  period).



      (c) The owner/operator should prepare a written construction quality



 assurance plan to be used during construction of the double liner system,



 including both the FML top liner and the composite  bottom liner.   See Section



 IV on Construction Quality Assurance for specific recofrmendations.








      Construction



      0  The  earth  substrates  and  base materials should be  maintained in a



 smooth,  uniform,  and compacted condition during  installation of each liner



 and components.



      0  Surface impoundment  and landfill units  should be constructed with liners



 that meet the following, as a minimum:






      (a) EML liners:



      (1) The liner should be installed  (seamed) at  ambient temperatures within



the range specified by the manufacturer of the particular liner.   Temperature



extremes may have an effect on transportation, storage, field handling and

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                                       20
 placement,  seaming,  and backfilling  (where  required).



      (2) When the field seaming of the FML  is  adversely affected by moisture,



 portable protective structures  and/or'other methods  should be



 used to maintain a dry sealing  surface.



      (3) Liner installation should be suspended when wind conditions may



 adversely affect the ability of the  installers to maintain alignment of



 seams and integrity of membranes and seams.



      (4) Field seaming of FMLs  should be performed when weather conditions



 are favorable.   The contact surfaces of the FML should be free of dirt,



 dust,  and moisture including films resulting from condensation in weather



 conditions of high humidity.  Seams  should  be  made and bonded in accordance



 with the supplier's  recormended procedures.  Both destructive and nondestructive



 testing  methods  should  be used  to evaluate  seam integrity.  All on-site



 seams  should be  inspected by nondestructive testing  techniques to verify



 their  integrity.   Periodic  samples should be removed from both factory and



 field seams and  tested  for  seam integrity by destructive tests (tension and



 peel tests).  On-site nondestructive seam samples should be made and evaluated



 with identical  liner material,  adhesive, and technique prior to actual field



 seaming  each day, or when conditions change.   Seam testing methods are described



 in more  detail in  an upcoming EPA report, Construction Quality Assurance for



 Land Disposal Facilities.



     (5) Proper  equipment should be  selected in placing bedding material




 over FMLs to avoid undue  stress.








     (b) Low permeability soil:



     (1) EPA is conducting  studies to evaluate the construction criteria



that most significantly influence the hydraulic conductivity of compacted

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                                       21
  low permeability soil liners.  Until specific research and/or demonstration



 data are available, the following are suggested as the best available procedures



 for optimizing construction of the compacted bottom conponent of the conposite



 liner:



      (i) Remove all lenses, cracks, channels, root holes,  or other structural



 nonuniformities that can1 increase the nominal in-place saturated hydraulic



 conductivity of the liner above 1 X 10~^ cm/sec.



     (ii) Construct the liner in lifts not exceeding 15 centimeters (6 inches)



 after compaction to maximize the effectiveness of compaction throughout the



 lift thickness.   Each lift should be properly interfaced by scarification



 between lifts.



    (iii) Scarify sufficiently between each lift so as  not  to create a zone



 of higher horizontal hydraulic conductivity at the interface of the lifts.



     (iv) Break  up clods  and homogenize the liner material  before compaction



 of each lift using mixing devices such as  pug mills or rotary tillers.   All



 oversized materials (such as trash,  large  roots,  wood,  or  large clods)  should



 be removed  in order to facilitate moisture control operations,  maximize



 compaction,  reduce heterogenity,  and minimize overall  hydraulic conductivity



 of the  compacted  liner.



      (v)  Thoroughly mix  in moisture  needed to bring the liner to the desired



water content using mixing devices such as pug mills,  rotary tillers, or



other effective methods.



    (vi) Compact the liner after  allowing  a sufficient time  for added water



to penetrate to the center  of the clods while  not  allowing so rruch  time



after water addition that  the exterior  of  the  larger clods becomes  drier



than optimum.  The  larger clods should  be  field checked for moisture distribution.



    (vii) Take the necessary precautions to assure  that the desired  moisture




content is maintained in the compacted  liner to avoid  desiccation cracking.

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                                       22
 Precautions that are effective at preventing desiccation cracking should be



 taken both between the placement of lifts and after conpletion of the liner.



    (viii) Construction should not take place using frozen or other indurated



 soil, and precautions should be taken to assure that the liner is not allowed



 to freeze after placement.



     (ix) Sidewalls should be constructed so as to minimize flow between the



 lifts.  EPA believes this can best be acooitplished with lifts  that are laid



 down parallel to the slope.




      (x) A demonstration should be made that sidewalls can be  effectively



 compacted at the maximum slope to be used in the design.   The  Agency suggests



 a maximum slope of 3 horizontal to 1 vertical.



     (xi) Consideration should be made of the vector of compactive effort



 when calculating the number  of passes necessary to obtain a certain degree



 of compaction on sidewalls.



    (xii) The uppermost lift  should be scraped and steel rolled to produce a



 smooth surface prior to placement of the EML upper component.   This procedure



 is intended  to minimize lateral flow between components of the composite



 bottom liner.



      (2) EPA recommends  that a representative test fill be constructed using



 the soil, equipment,  and procedures  to be used  in construction of the compacted



 low permeability soil component to the composite liner in the  full scale



 facility.  The test  fill should be used to verify that the specified density/



 moisture ccntent/hydraulic conductivity values  can be  consistently achieved



 in the full scale facility.  Test  fills have been used to validate both



 design and construction procedures for critical earthen structures around



 dams and nuclear power plants.   In order for the data  collected from the



 test fill to be useful, however, construction control  of  the test fill must




be strict and well documented.

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                                        23
       Previously-developed data that describes the performance  of an installed



  liner can be used, provided documentation is available on all  the  factors



  discussed above.   EPA is not,  however'aware of any  facility that currently



  has this data on loand.




       All information gathered  during construction and  subsequent testing of



  the test fill should be documented.   The  CQft. program to be  followed during



  ccnstruction of the full scale facility should be strictly  followed during



  construction of the test fill  (Corps of Engineers, 1977).   Recommended mininum



  test fill ccnstruction details are as follows:




       (i)  Construction using the same compactable materials, compaction equipment,



  and exact procedures  as will be used to construct the full  scale facility




  liner.  All applicable parts of the quality assurance plan should be precisely



  followed  to monitor and  document construction of the test fill.




      (ii) The test fill should be constructed at least four times wider than the



 widest piece of equipment to be used in construction of the full scale facility.



     (iii) The test fill should be long enough to allow construction equipment



 to reach normal operating speed before enterino the  area to be  used for testing



  (see Figure 6).



     (iv) Construction so as  to facilitate  the use of field hydraulic conductivity



 tests and/or a complete quantification of  all underdrainage. Field hydraulic



 conductivity tests should be  conducted on  the compacted test fill material as



 a verification of  results of  laboratory tests conducted on undisturbed samples



 taken frcm the compacted test fill material.   The field hydraulic conductivity



 tests need only verify that the hydraulic  conductivity  is  1  X 10~7  on/sec or




 less,  not  its  actual value.  These undisturbed samples  can then be  used for



 compacted  liner/leachate  compatibility testing.



      (v) Construction so  as to  determine the  relationship  of the following to




the moisture ccntent/density/hydraulic conductivity values obtained in the



field:

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                                Figure 6
    AT LEAST  THREE SIX-INCH THICK LIFTS OF COMPACTED SOIL

    A DRAINAGE LAYER OR UNDERDRAlNAGE COLLECTION  SYSTEM

                                                                            UJ
                                                                            a.
                          2:I   SLOPE
L« DISTANCE REQUIRED FOR CONSTRUCTION EQUIPMENT TO REACH NORMAL
   RUNNING SPEED
W DISTANCE AT LEAST FOUR TIMES WIDER THAN THE WIDEST  PIECE  OF
   CONSTRUCTtOM EQUIPMENT

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                                       25
      0  Compaction method (detailed  specifications of the caipaction equipment);
      0  Number of passes of the compaction equipment;
      0  Mixing method (and resulting raxinum clod size);
      0  Conpaction equipment speed;  and
      0  Unconpacted and compacted lift'thickness.

    (vi) A set of index properties should be selected that will be used to

 monitor and document the quality of construction obtained in the test fill.

 These index properties should include at least the following:
      0  Hydraulic conductivity (undisturbed samples);
      0  In-place density and water content;
      0  Maximum clod  size;
      0  Particle size distribution; and
      0  Atterberg limits.

 Data from these tests  shall be used as standards for comparison with values

 obtained  on samples  from the  full scale liner to indicate inplace field

 hydraulic conductivity.

      (3)  All lifts of  the compacted low permeability soil liner that are

 part of the 3-ft  minimum thickness should have a in-place hydraulic conductivity

 of  1X10"7 cm/sec  or  less.  This hydraulic conductivity value should be

 verified  both  in  the test fill liner and by the comparison of index property

 values  between the test fill  and each lift in tlie full scale liner.  The

 values  obtained should be numerous enough to fully document the degree of

 variability of all the index properties in both the test fill and each lift

 in the  full scale liner.

      (c)  The owner/operator should implement a written quality assurance

plan for monitoring and documenting the quality of liner materials used and

the  conditions  and manner of  their placement during construction of the top

FML  and composite bottom liners.  See Section IV on "Construction Quality

Assurance"  for specific recommendations.

      (d) The documentation for the CQA program for construction of the double

liner should be kept on-site in the facility operating record.

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                                        26
      Operation

      The following operational  criteria apply:

        (a)  The top (FML)  liner  should prevent migration of waste constituents

   into the  liner through  the closure period, except for de minimis leakage.

        (b)  The placement  of removable coupons of the EML above the top liner

   is a technique for providing waste/liner chemical compatibility information

   during the operating period.  Coupons are samples of the FML's used in the

   construction of  the tvo liners that are placed in contact with wastes or

   leachate  in  the  landfill or surface impoundment.  The coupons are tested

   after various  exposure periods in the unit to determine how the properties

   of the liner change over the operating period.  This information,  when compared

   to short-term compatibility data, can provide an early warning that the

   liner  is degrading faster than anticipated and allow for corrective measures

   by the  owner.  The Agency reccnmends that landfill and surface impoundment

   owners consider removable coupon testing if wastes are likely to vary somewhat

   during operation.

     (c) The owner should have en-site guideline? for operation and maintenance

of the double liner system,  which include recommendations on such subjects

as:

       - Frequency and documentation of inspection,
       - Testing and repair  of liner,
       - Animal and plant  control,
       - Erosion control,
       - Unacceptable practices,
       - Placement of waste, and
       - Coupon test schedule  (optional).



       B. Discussion

       The EPA  believes  that an  FML used in this double liner system,  whether

  the  top liner or  the upper component of a composite liner,  should meet the

  following  criteria:

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                                       27
      - A minimum thickness depending on the service;

           0 For buried FMLs the mininum thickness should be 30 mils when the
             membrane will be covered within three months by a protective layer
             against mechanical and weather conditions.

           0 For membranes that will be buried,  but left unprotected for periods
             greater than 3 months, the mininum thickness should be 45 mils.

           0 For all liners used in impoundments that  are left uncovered and
             exposed to the weather and experience light work on the surface,
             the minimum thickness should be 45 mils.

           0 The thickness of scrim layer,  geotextile  backing,  or "other reinforcing
             material should not be used in computing  a  minimum, recommendation.

           0 For many units, particularly surface impoundments with exposed surfaces,
             FML's of 60-100 mils may be required to meet the mechanical stress
             requirements.

           0 The stresses on exposed liners are generally greater for surface
             impoundments because of exposure to more  severe environmental conditions
             (climate),  loading and unloading during daily operation,  and sludge removal.
             Because of  the more severe operation conditions,  surface impoundments
             require substantially thicker liners.   A  protective layer covering the
             liner can reduce the stresses on the liner.

      -  Sufficient strength to  prevent failure due to  pressure gradients
        (including static head  and external hydrologic forces,  stresses of
        installation,  and the stresses of daily  operation);
      -  Compatibility with  the  waste to be  managed in  the unit;
      -  Low permeability; and
      -  Capable of being seamed to produce  high  strength,  liquid-tight seams
        that  retain their integrity during  liner installation  and on exposure
        to wastes  for the duration of the operating life  of the unit,  including
        the postclosure monitoring period.

      One of  tlie primary  reasons for failure of  synthetic liners is  damage

 (i.e., punctures,  rips,  and tears).   Damage occurs during installation and/or

during operation.  The owner operator needs to  demonstrate that the selected

FML thickness  is adequate  for  the site-specific conditions  the liner will

encounter while the unit is  in operation (including any  post-closure monitoring

period).

     EPA believes thickness and strength of the liner material  are  major

factors in maximizing serviceability and durability.  However,  the  lack  of

current technical data relating liner thickness for specific material  types

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                                      28
 to successes  and  failures of  liner systems prevents more specific guidance

 on thickness.  The  following  is a list  (EPA, 1983) of potential failure

 modes  that should be considered in selecting the FML polynver type and thickness

 to maximize liner serviceability and durability:

     Physical Modes of Failure

     Abrasion
     Creep
     Differential settling
     Hydrostatic  pressure
     Puncture
     Stress-cracking (partly  chemical)
     Tear  stress
     Thermal stress

     Chemical Modes of Failure

     Extraction of plasticizer and soluble ingredients
     High  pH>10
     Hydrolysis
     Attack by ionic species
     Low pH<2
     Ozone-cracking
     Attack by solvents and organic chemical species
     Ultraviolent light attack

     Biological Modes of Failure

     Microbial attack (of plasticizers in FML compounds)

     Liner failure mechanisms are addressed in a U.S. EPA Technical Resource

Document,  Lining  of Waste Impoundment and Disposal Facilities, SW-870,

March  1983.  This document describes and discusses the categories and charac-

teristics of liner failure in a service environment.  The document is available

from the U.S.  Government Printing Office, publication number S/N 055-000-00231-2,

$11.00, Superintendent of Documents,  Washington, D.C.  20460.  Kays (1977)

also provides detailed discussion on liner failure mechanisms and methods to

avoid failures for cut-and-fill reservoirs.

     EPA believes that,  for design purposes, the post-closure monitoring

period can rominally be assumed to be 30 years.  The double liner system.

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                                      29
 should be designed so that no leakage out of the unit is expected through



 the operating period, including the 30-year post-closure monitoring period.



    To help guard FMLs against damage, such as punctures, tears,  and rips



 due to contact with sharp objects or other conditions,  it is good practice to



 protect them from above and below by a minimum of 12 inches of bedding material.



 In landfills, the act of placing wastes sometimes causes damage (e.g.,  due to



 dropping of wastes or driving of vehicles on the liner); also,  over extended



 time periods the wastes themselves may be capable of causing damage to the



 top FML and to the leachate drainage and collection system because they contain



 sharp objects or abrasives.



      For landfill units,  a leachate drainage and collection system nust be



 placed above the top liner.  This layer can be made of  materials that meet



 both bedding and drainage material requirements.   However,  EPA suggests



 that for these units an additional layer of bedding material be installed



 above the top filter layer as well as below the top FML, unless it is known



 that the FML is not  physically  impaired by the materials,  including pipes in



 the secondary leachate  collection system.   The Jrain pipes  in both collection



 systems  should be  adequately protected against damage caused by waste placement



 and/or  equipment operating on the working surface.



     Bedding  layers  should consist of materials that are no coarser than



 sand  (SP) as  defined by the Uniform Soil Classification System (USCS).   Use



 of a sand layer  is corrmon practice for protection of membranes  and pipes



 from damage due  to contact with grading equipment and materials,  sharp materials



 in the soil,  etc.  As discussed above,  the bedding layer need not be a separate



 layer, as the materials in  the secondary leachate detection,  collection,  and



 removal system will often meet the  necessary criteria.



     For surface impoundments, a bedding layer above an FML also protects the



FML from damage due to exposure to  sunlight and wind while  the unit is  in

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                                      30
operation.  However, the bedding material is not always necessary above the



top  liner, since direct contact with the liquid wastes does not represent



the  same potential for puncture that is present in landfills.  Nevertheless,



the  liner  can be damaged during sludge removal or other dredging operations.



Where mechanical equipment is used, EPA recommends a minimum of 45 centimeters



(18  inches) of protective soil or the equivalent covering the top liner,



unless it  is known that the EML will not be damaged by the sludge removal



practices.  Some EML materials are known to be degraded by ultraviolet radiation



and  must be covered.  Also, wind can get under the edge of exposed EMLs,



causing flapping and whipping, which can lead to tears.  These problems have



occurred most commonly above the liquid level near the edge of the FML.  As



a result,  it is common practice to cover FMLs with 6 to 12 inches of earthen



material to prevent degradation due to sunlight and hold the liner down.



The  edges of BMLs are usually secured by anchor trenches at their perimeter.



Of course, if the design is such that wind creates no difficulties, and if



it is known that tiie FML is not subject to solar degradation, then these



precautions are not necessary.  The addition of a cover over the EML is



expected to extend the service life of the liner.  The bedding material need



not be a separate layer, as the secondary leachate detection, collection,



and removal system materials will often meet the necessary criteria for




bedding.



     Chemical testing of all construction material components is prudent



because liners can be degraded by certain chemical species that may be present




in the waste.  Because wastes and liner chemical characteristics are almost



infinitely variable, it is difficult to generalize concerning incompatibility



or compatibility.  The Agency, therefore, strongly suggests  (and prefers)



test data as the appropriate way to demonstrate the compatibility of the

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                                       31
 waste to be managed and the liner naterials  under  consideration.  Test results



 should demcnstrate the acceptability of the  selected  liner materials.  New



 test data may not be needed for units-that have  a  well defined waste conposition



 and for which previous test data showing that the  proposed liner  chemical



 characteristics are very predictable.



      Waste liner material compatibility tests should  be  conducted using



 representative sanples of wastes and leachates to  which  the  liner is to be



 exposed.   Several methods for obtaining sanples  of hazardous waste are discussed



 in Section one of Test Methods for Evaluating Solid Waste  (SW-846).



      An acceptable test method for assessing the compatibility of waste



 liquids and EML's is  the "Immersion Test of  Membrane  Liner Materials for



 Chemical Compatibility with Wastes," found in EPA's Method 9090.  In this



 test,  samples of the  candidate EML's are ijrmersed  at  two temperatures in



 sanples of the waste  liquid to be  managed and exposed for  four months.



 After  exposure for one-month intervals,  an FML sample is tested for important



 strength  characteristics (tensile,  tear,  and puncture) and weight loss or



 gain.   The Agency considers any significant  deterioration  in any  of the



 measured  properties to be evidence of incompatibility unless a convincing



 demonstration can be made that the deterioration exhibited will not impair



 the liner integrity over the life  of the facility.  Even though the tests



 may show  the  amount of deterioration to  be relatively small, the  Agency is



 concerned about  the cumulative effects of exposure over  very much longer



periods than those  actually tested.



     At present,  no standard test  method is  available for  assessing the



compatibility of  specific  low permeability soils with a  given waste liquid.



Nevertheless, the compatibility of a soil with a waste liquid has been measured



by comparing the permeability of the soil to water and to  the waste liquid.

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                                      32
     The Agency incorporated the National  Sanitation Foundation's  (NSF)



standard specifications for flexible membrane liners into this guidance to



provide suggested minimums values for'physical properties.  An NSF committee



has been studying the subject for some time,  and  EPA believes that the



specifications developed are reasonable and well  thought out.  Compliance



with the NSF standard attests only to the  basic quality of  the liner  itself



and not to the advisability of its application under any given set of waste




and unit-specific circumstances.



     The top liner, an FML, is required to prevent  migration of constituents



of the waste liquid into the liner during  the period the unit remains in



operation (including any post-closure monitoring  period) except for de minimis



leakage.  EPA recognizes that membranes will  not  always have zero leakage



and that de minimis leakage may occur.  De minimis  leakage  can occur  as a



result of vapor passing through the liner, very small  imperfections  in the



liner that occur very rarely, or a seam that  has  a  very small crack or hole.



Although FML's are nonporous-honogeneous materials, vapor diffusion can transmit



water and other liquids with dissolved constituents through synthetic liners.



The transmission involves (1) sorption of  the constituents  of the waste



liquid into the membrane, (2) diffusion through the FML,  and  (3)  evaporation



or dissolution of the constituents on the downstream side of  the  membrane.



The principal driving force for permeation through  an  FML is  the  gradient



across the liner in concentration, chemical potential, or vapor pressure  of




the individual constituents in the liquid or vapor.  Permeability of an



individual permeant depends upon its solubility and diffusion characteristics



in a specific liner.  De minimis leakage can also occur because of small and



infrequent breaches in the liner that were not detectable during construction



with current practical state-of-the-art construction quality assurance programs.

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                                       33
 Detected leakage tray be clue to Leakage through either the  top or bettor;



 liner.



      EPA believes that current state-Qf-the-art technology for FML installation



 allows for hazardous waste management units to be built  that will  have  very



 low leakage rates at installation.   EPA does not have a  specific maximum de



 minimis leakage rate that can be recommended.   However,  based on currently



 available preliminary field data,  laboratory test results,  and professional



 judgment,  EPA believes that de minimis leakage should be approximately



 1 gal]on/acre/day or less.   This rate should not be  taken  as a hard and fast



 rule because there are conditions where vapor transmission potentially



 could exceed this value.  Also,  this value does not  apply  to organic  liquids,



 many of which can permeate  an FML independently of the water in waste liquid.



 Some organic constituents can transmit at  considerably higher rates than



 water,  if  the organic constituents  are soluble in the membrane and organic




 concentration en  the downstream side of the membrane is  essentially zero.



 Dr.  H. August et  al,  (1984),  has  shown laboratory permeation rates for



 concentrated hydrocarbons on 1 mm thick HOPE FML's were  between 1  and SOg/rt^/day



 varying with the  waste chemical  structure  and its affinity to the  HDPE.



 Another finding of this study was that very dilute hydrocarbon solutions



 sometimes give high permeation rates of the hydrocarbons because of the



 relatively high solubility  of the hydrocarbons cortpared  to water in the



 HDPE.  The concentration  of organic waste  in the liner surface can be higher by-



 several orders of magnitude than the  adjacent  leachate or  liquid waste  containing



hydrocarbons.  Current laboratory tests  cannot be related  directly to estiinate



 field rates of permeation because the  tests  do not simulate the ability ©f



soil under the liner to transport the waste  away from the  liner.   (See  the



suggested reading material  list for additional information.)   Review  of

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                                      34
 infonration from recently constructed double synthetically lined surface




 inpoundments shows  that current state-of-the-art technology for installing




 synthetic  liners  is close to achieving 100% containment efficiency.  The




 liner installations studied had extensive construction quality control to




 assure the seams  did not leak.




      A conposite  secondary liner including both FML and compacted soil




 conponents was selected as a result of various studies and analyses conducted




 by the Agency.  A conposite liner has several advantages.  The FML component




 inproves the efficiency of the secondary leachate collection system that




 must  be installed between the top and bottom liners (see Section III).  Any




 improvement in the  collection efficiency of this system would allow earlier




 detection  of liquids between the liners.  Capillary forces present in an unsaturated




 low permeability  soil liner may cause the initial leakage through the top




 liner to be absorbed before it is detected.  FMLs on the other hand, can




 achieve virtually complete rejection of liquids and are, thus, more effective




 than  compacted soils at detecting small amounts of leachate and overall




 removal efficiency.  For this reason, a FML was= selected for the upper conponent




 of the bottom liner.



      While  less efficient at detecting initial top liner leakage, compacted




 low permeability soil liners are not subject to the same types of installation




and operational problems as FMLs.  A problem that causes a puncture in a




FML probably will not form a hole all the way through a compacted soil liner.




In addition, a compacted soil liner has a potential to both minimize leakage




through the FML and attenuate certain constituents in the leachate in the




event of a  leak.  In the event of leakage through the FML component of the




composite liner, the low hydraulic conductivity (1X10~7 cm/sec or less) in




the compacted soil  liner would have the effect of both decreasing this leakage

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                                       35
 and increasing efficiency of the secondary leachate collection system.   For

 these reasons, a conpacted low permeability soil liner was selected as  the

 lower component of the corrposite bottom liner.  The conpacted soil is a low

 permeability soil that has been compacted in 6-in.  lifts,  with an inplace

 hydraulic conductivity of 1 X 10~^ cm/sec or less.   For purposes of this draft

 guidance, "compacted soil" is not meant to include materials such as soil cement,

 lime soil mixtures,  or fly ash soil mixtures,  and other soil amendments including

 natural or man made.

      Objectives of the conpacted low permeability soil component of the

 composite bottom liner include the following:

      (1) to serve as a protective bedding material for the FML upper component;

      (2) to serve as a long term structurally stable base  for all overlying
          materials;

      (3) to attenuate constituents in liquids  that  might leak through the
          FML upper component;  and
                                               j
      (4) to minimize the  rate  of leakage  through breaches  in the
          FML upper component.

     Objective number one can  be met  if the  compacted soil is smoothed  prior

 to the placement of  the FML upper component.   In most cases,  three feet of

 compacted low permeability soil  will  be adequate to meet objective number two.

 However,  the adequacy of  a given conpacted thickness will  depend on the soil

 being conpacted,  the  degree of compaction, the total expected load,  and the

 geologic and hydrologic setting.  Documentation  should  be provided that

 describes the  capability  for a given  thickness to both  serve as  adequate

 bedding  and provide sufficient structural  support.

     Objective three,  attenuation of  constituents,  can  best be met by as-suring

that the conpacted soil is  as homogeneous  as possible.  Preventing the  formation

of cracks  (by preventing desiccation  or freezing of the  liner during or

after placement) and reducing the number of large pores  (by reducing clod

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                                      36
 size and optimizing conpactive procedures) are two ways to enhance the atten-

 tuative capacity of the soil  liner.  If leachate has only relatively small

 pores through which to migrate, the waste constituents come in closer contact

 with the adsorptive surfaces of the conpacted materials.  One way to document

 the  attenuative  capacity of a given thickness of conpacted soil is through

 the  use of breakthrough curves (Griffen, 1978 and Anderson, 1982).  To closely

 simulate actual  field conditions, these breakthrough curves should be determined

 on undisturbed samples of the conpacted soil collected from the test fill.

      Objective four can be achieved by minimizing both the potential for

 lateral flow  between the FML upper and compacted lower components of the

 bottom liner  and by minimizing the flux of liquid through the compacted

 lower component.  Lateral flow between the components of the bottom liner

 can  be  minimized by obtaining a good contact between the compacted lower component

 and  the FML upper component. -This contact is obtained by a combination of

 the  following:

      (1)  smoothing  the top of the uppermost lift of the conpacted soil by
 use  of  smooth wheel steel rollers; and

     •(2)  application of overburden pressure to the top of the FML upper
 component.

     Overburden will be supplied by the weight of the overlying leachate collection

 layer,  and waste (in the case of surface impoundments) and by the leachate

 collection layer, waste, and final cover (in the case of landfills).  Additional

procedures and materials are encouraged that may further reduce the lateral

 flow between the secondary liner components.

     Minimizing the flux of liquid through the compacted soil can be accomplished

 as follows:

      (1) minimizing the hydraulic gradient under which leachate will move; and

      (2) minimizing hydraulic conductivity of the compacted soil.

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                                       37
 There are two ways  to minimize the hydraulic gradient:  (1) reduce the depth

 of standing liquids in the  leachate collection systems; and  (2) construct a

 thicker compacted soil liner.  Besides  lowering the hydraulic gradient,

 constructing a thicker compacted  liner  should reduce the probability that a

 blemish of any kind would penetrate all the way through the compacted soil.

      Whether referred to as blemishes,  macrof eatures, or structural non-unifor-

 mities,  construction  inperfections may  increase the overall saturated hydraulic

 conductivity by several orders of magnitude.  Methods to reduce actual in-the-

 field hydraulic conductivity of a conpacted soil should be included in the

 construction inspection program to both prevent and detect these imperfections.

 Details  of the  information that should  be gathered before, during,  and after

 construction of a compacted soil  (which should serve to reduce the number of

 these inperfections) are given under "Construction Quality Assurance" (section IV),

     Hydraulic  conductivity testing on the in-place conpacted low permeability

 soil is recommended because of concern that laboratory tests tend to under-

 estimate the  actual hydraulic conductivity in the field by a factor of 10 to

 1000.  The following recent references discuss the causes and magnitude of

differences between field-measured and  laboratory-measured hydraulic conductivity:

     0 Daniel, D.  E:,  1984.   Predicting Hydraulic Conductivity of Clay liners.
       ASCE Journal of Geotechnical Engineering,  110(2):235-300.

     0 Griffin, R. A.  et al. 1984.  Migration of Industrial Chemicals and
       Soil-waste  Interactions at  Wilsonville,  Illinois.  In:  Proceedings
       of the Tenth Annual Research Symposium on Land Disposal of Hazardous
       Waste (EPA  600/9-84-007) USEPA Municipal Environmental Research Laboratory,
       Cincinnati, OH  45268.

     0 Herzog, B.  L. and W.  J.  Morse.   1984.   A Comparison of Laboratory and
       Field Determined Values of  Hydraulic Conductivity at a Waste Disposal
       Site.   In:  Proceedings of  the  Seventh Annual  Madison Waste  Conference.
       University  of Wisconsin-Extension,  Madison,  Wisconsin,  p.  30-52.

     0 Boutwell, G.P.  and V.R.  Donald,  1982.   Conpacted  Clay Liners for Industrial
       Waste Disposal,  Presented ASCE  National Meeting Las Vegas, April 26,
       1982.

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                                       38
      One reason why higher hydraulic conductivities are often obtained with



 field tests is that sanples used in laboratory tests can be more readily



 prepared without the defects that can .greatly affect actual hydraulic conductivity.



 Methods that are used to prepare soil  liners  in the field are difficult to



 sinulate in the laboratory.   One exanple  is the method of compaction.  Soil



 liners are often corrpacted in the field with  a kneading action through the



 use of sheepsfoot rollers.   In contrast,  soil liner sanples are usually



 prepared in the laboratory using impact conpaction.  Even though "identical



 densities may be obtained with different  methods of compaction, the soil



 samples conpacted by different metliods may have very different hydraulic



 conductivities (Mitchell,  1976).



      There are a variety of other reasons for the large discrepancies reported



 between laboratory and field tests.  Samples  prepared in a laboratory are



 not subject to the climatic  variables  (such as cracking due to either freezing



 or  desiccation)  (EPA 1984A).   There may also  be a tendency to run laboratory



 tests on samples  of selected finer textured soil materials (Olson and Daniel



 1981).   It is often suggested, however, that  the most important reason for



 observed differences  is  that field tests  can  evaluate nuch larger and, hence,



 more  representative'samples  than is practical in laboratory tests.



      EPA believes  that field hydraulic conductivity tests are essential to



 verify the requirement  to have an in-place hydraulic conductivity of 1X10~7



 cm/sec or less.  Currently available field hydraulic conductivity tests, if



 conducted on  the  actual  compacted soil liner  may, however, cause substantial



 delays in  construction  and result  in other problems due to prolonged exposure



 of  the liner.   In  addition,  it would be extremely costly if it were determined



 from  field tests on the  actual liner that it  did not meet or exceed performance



 standards.  Much time  and effort can be saved if, prior to construction of




the actual  liner, a test section of the liner is prepared and tested.  These

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                                       39
 tests can be used to document the capability of the proposed materials and




 construction procedures that result in a ccrpacted soil liner that meets the




 desired performance standards.  Therefore,  the EPA recommends that a test




 fill be constructed using the same borrow soil,  compaction equipment,  and




 construction procedures as proposed for the full scale facility.   The test




 fill is also recommended for use in demonstrating the actual in-place hydraulic




 conductivity of the compacted soil liner.




      Field hydraulic conductivity tests of the compacted soil in  the test fill




 are necessary to assure that the materials and procedures used in the field




 will result in a compacted soil liner with a hydraulic conductivity of IXICT^




 on/sec or lower.   Field testing is not intended to preclude the use of laboratory




 testing in the design or construction phase or as a means of evaluating




 liner-leachate compatibility.   It is expected that the overall design and




 construction quality assurance (OQA)  program will include a mixture of both




 field and laboratory hydraulic conductivity tests.




      As  appropriate methods are developed and verified,  the EPA intends to




 require  field hydraulic  conductivity tests  be conducted on the full scale




 facility.   Field  hydraulic conductivity tests can be performed in the test




 fill  without causing delays during construction  of the full scale facility.




 The field test used should be  capable of verifying that the hydraulic conductivity




 of the compacted  soil liner is  1X10~^  cm/sec or  less.




     Field infiltrometers  capable  of  measuring very low hydraulic conductivities




 in compacted soil liners have been developed and reported by Anderson et  al




 (1984), Day  (1984),  and Day et  al  (1985).  An alternative to the  use of field




 infiltrometers is the use  of a  system for capturing and collecting all under-




drainage from the test fill.  Day  (1984) used such an underdrain  to evaluate




the accuracy of results obtained from field  infiltrometers.  While the field




infiltrometers were found to accurately measure hydraulic conductivity, the

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                                      40
 underdrain was considered aven More accurate.

     Both infiltration and underdrainage tests should be conducted until

 stable flew and/or drainage rates are obtained.  Where infiltrometers are

 used, there should be enough replicate tests to document areal variability

 in the hydraulic conductivity of the liner to the test fill.  A sufficient

 number of index property tests (listed earlier in this section) should be

 conducted to acconplish the following:

     (1) verification of the aspects of the CQA plan related to compacted
         soil liners; and

     (2) document the degree of variability in each of the properties tested
         in the compacted soil liner for both the test fill and full scale facility

     In addition to being used as a site for field hydraulic conductivity

 tests,  the test fill should be used to verify all elements of the design and

 construction of the soil liner.  These elements should include at least the

 following:

     (1) verification that the proposed soil material is uniformly suitable
         to be compacted into a liner (i.e., no cobbles, sand lenses, or indurated
         rraterials).

     (2) verification that the equipment and procedures for breaking up
         clods, mixing in water,  and compactinc, the soil are suitable for
         consistently achieving the required hydraulic conductivity specifi-
         cation.

     (3) verification that the CQA plan is sound in all respects.  The proposed
         CQA plan for construction of the full scale facility should be
         followed exactly as applied to construction of the test fill.  If
         methods to improve the CQA plan are documented during construction
         and testing of the test fill, these improvements should be  incorporated
         into the CQA program implemented during full scale facility construction.

     Technical personnel who will be in charge of day to day implementation

of the CQA plan on the full scale facility should also monitor and thoroughly

document construction and testing of the test fill.  This documentation

should include at least the following:

     (1) a detailed description of the type of equipment used during the
         borrow and construction operations,

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                                       41
       (2)  location of work, including borrow and construction sites;

       (3)  size, location, number, and identification of test sanples collected
           and results of all tests performed;

       (4)  a diary of all relevant climatic and working conditions that may
           affect construction of the full scale liner;

       (5)  index of all tests and results that will be used to compare the
           liner constructed in the test fill to the full scale liner; and

       (6)  test fill report that compiles all documentation on the construction
           of the test fill and includes all raw data and test results.

      Laboratory hydraulic conductivity tests should be conducted"on undisturbed

 sanples collected from the soil liner in the test fill.  Care should be

 taken to avoid conditions that bias test results.  Examples of these conditions

 include excessive effective confining pressure (Boynton and Daniel, 1985;

 Anderson,  1982)  and sidewall flow (Daniel et al 1985).  Methods for collecting

 undisturbed samples of soil liners  have been suggested by Anderson et al

 (1984) and Day (1984).   The undisturbed samples may not provide hydraulic

 conductivity values  that precisely  reflect field values.   However,  comparison

 of values  obtained  from the test fill and full scale liners should provide

 an indicator of gross  changes  in either the materials or procedures used in

 construction.

      EPA believes that  additional testing is warranted to evaluate the hydraulic

 conductivity of landfill  and surface  impoundment sidewalls.   Especially in

 surface  impoundments, the sidewalls may be the predominant pathway by which

 leachate can migrate beyond the  liner systems.   At  this time however,  the

Agency is  not aware of a suitable method for evaluating hydraulic  conductivity

of the sidewalls other than by construction of a costly scale  impoundment.

There would need to be separate underdrains  for the  sidewalls  and  bottom

portions of the liner or it would be difficult  to determine how much each

portion was contributing to the total underdrainage.   EPA is temporarily

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                                      42
 deferring the recommendation for sidewall testing to allow interested parties

 to develop economical and effective test methods.  Comments are requested on

 the follev/ing:

      (1) Are tests of the hydraulic conductivity of landfill and surface
         impoundment sidewalls necessary?

      (2) Are there methods available for evaluating the hydraulic conductivity
         of sidewalls?

      (3) Are there additional methods that should be developed to facilitate
         this testing?

      In construction of FMLs, consideration should be given to the effects

 from humidity in the air.  Seaming of EMLs with some solvent cements at

high  levels of relative humidity can result in moisture condensation on the

adhesive surface during the seaming process and may result in poor adhesion.

A relative humidity requirement may not be necessary for seaming techniques

that rely on heat to bond the liner sheets,  as the heat could prevent moisture

from condensing on warm surfaces of the FML.

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                                      43
         III.   Secondary Leachate Collection System Between The Liners


                                   Contents

                                                                 Page

 A.   Guidance   ------_-__--------------    43

        Objective	     43
        Design  --------------------- — -    43
        Construction ---------------------    45
        Operation -----------------------   45

 B.   Discussion	   46
   A.  Guidance

   Overall Design, Construction and Operation Objective

     The system should be capable of rapidly detecting, collecting, and removing

 liquid entering the collection system; be constructed of materials that can

 withstand the chemical attack that results from wastes or leachates, and the

 stresses and disturbances from overlying wastes, waste cover materials, and

 equipment operation; be designed and operated to function without clogging;

 and be operated to detect, collect, and remove liquid through the post-closure

 care period.  This guidance also sets out methods for proper installation

 of components to assure that the specified performance of the leachate collection

 system is achieved.

     Design

     The secondary leachate collection system should have:

     (a)  A drainage layer that will permit rapid detection, collection, and

 removal of any migration of liquid into the space between the liners.  The

drainage layer should also be designed to collect and remove liquids rapidly

and to produce little or no head of liquid on the bottom liner.

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                                       44
      (b) Materials that are chemically  resistant  to the waste and leachate,



 a minimum bottom slope of 2 percent,  and a minimum hydraulic conductivity of



 1X10"2 cm/sec.



      (c) A system of drainage pipes of  appropriate size and spacing on the



 bottom of the unit to efficiently  remove leachate.



      An innovative leachate collection  system such as a synthetic drainage



 layer will be considered  by the Agency  if it can be demonstrated to be equivalent



 to a conventional granular system  with  pipes and meets (a) and (b).  These



 materials must be chemically resistant  to the waste and leachate; they must



 be compatible with and non detrimental  to the FML and not collapse under the



 designed load.



      (d)  Direct contact with the FML component of the bottom liner.



      (e)  A sump of appropriate size to  efficiently collect leachate and be



 positioned at least 30  centimeters (12  inches) below the drainage layer



 grade.   Each  landfill  or  surface impoundment unit should have its own sump.



 For landfills,  the  sump for the secondary leachate collection system must be



 separate from the primary  leachate collection s>imp.



      (f)  A collection system that cover all areas between the double liners



 likely to  be  exposed to waste and  leachate.



      (g)  Methods of measuring and  recording fluid volumes in the collection



system sump.



      (h) The  owner/operator should implement a written construction quality



assurance plan during construction of the double liner system, including the



secondary  leachate collection system.   See Section IV on Construction Quality




Assurance for specific details.

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                                       45
      Construction



      (a) The owner or operator should use the construction quality assurance



 plan to monitor and document the quality of materials used and the conditions



 and manner of their placement during construction of the collection system



 of the unit.



      (b) The documentation of the CQA program should be kept on-site in the



 facility operating record,



      (c) The secondary collection system,  including sump,  should be free of



 liquids and hazardous constituents when the waste management unit begins



 operation.



      Operation



      The following operational measures should be followed;



      (a)  Removal of liquids,  if any,  on a daily basis,  minimizing the head on



          the ccnposite liner;



      (b)  The owner or operator should establish an inspection schedule  that



 will allow him to determine that the  system is functional  and operated  properly.



 EPA recommends that the removal sump  be inspected for the  presence of liquids



 and proper operation  of the system on each operating day or,  at a miniiajm,



 weekly  during the active life  depending upon site-specific conditions,  and



 at  least quarterly during closure and post-closure.   The owner or operator



 should keep records on the system to  provide sufficient information that the



 secondary leachate collection  system  is functional and  operated properly.



 Documentation may include the  amount  of leachate present in  the detection,



 collection,  and removal  system of the unit.   This  information should be



 recorded in the facility operating record;



      (c) Repair of damaged leachate collection system corrponents as  soon as



practicable during the operating  period;

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                                      46
      (d) As a general matter EPA will include in draft permits a requirement

that  the owner or operator notify the Regional Administrator, in writing,

of  the presence of liquids in the secondary leachate collection system in a

timely manner.  Such notification may include, if necessary:

      (i) leakage rate (quantity);

    (ii) the concentrations of hazardous constituents [indicator parameters specified

         by 264.98(a)].

      EPA may, on a case-by-case basis, consider requiring owners and operators

of permitted units to respond to leaks in the top liner, if this requirement

is necessary to protect human health and the environment.

      (e) A storage permit for collected leachate, if required.

If the unit is not yet permitted (i.e., it is an interim status unit), the

owner/operator should modify the Part B application indicating the unit has

liquids in the secondary leachate collection system.  The Agency will consider

this  information at permitting to determine if the liner is leaking.

     B.   Discussion

     The Agercy believes that it is practical t^ design and operate a secondary

leachate collection system to rapidly detect liquids in the space between the

liners,  minimize the head on the bottom coitposite liner, and remove leachate

for treatment.  The specifications presented here, judiciously applied, are

expected to accomplish these requirements.

     The following is a list of factors that affect liquid transmission in

the drain layer of the leachate collection system:

     0 Impingement rate  of liquid on the collection drain layer;

     0 Slope of the drain layer;

     0 Size and spacing of the drainage pipe; and

     0 Hydraulic conductivity of the saturated sand or gravel drain
       layer.

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                                       47
      Drainage pipe diameter and spacing are inportant because they affect

 the time to liquid detection, rate of removal,  and the head that builds up

 on the bottom composite liner between pipes.  The pipe diameter should be

 large enough to efficiently carry off the collected leachate rapidly.   Since

 the philosophy for all aspects of liner design is to minimize the transmission

 of waste constituents through the liner system,  the head on the bottom liner

 should be minimized.   The closer the pipes are together,  the more quickly

 liquids are likely to be detected.   However,  the spacing and size of the piping

 system necessary to accomplish this  depends on other characteristics of the

 drain layer (e.g.,  hydraulic conductivity) and on the impingement rate of

 liquids  from the leak.   Unlike the primary leachate collection system  for

 landfills and piles,  the secondary leachate collection system detects  liquids

 as well  as  collecting and removing them.   Thus,  pipe size and spacing  need

 be sufficient for rapid  transmission of liquids  and need not be  designed to

 remove some predetermined  volume  rate of  flow.   EPA is,  therefore, not specifying

 minimum  spacing or  size  in this guidance.  Nevertheless,  a  reasonably  sized

 drainage system, coupled with  an  efficient sump  system Jor  removing collected

 liquids, will result  in the capacity to remove leaking liquids,  except in

 the case of severe breaches of the top liner.

     Innovative secondary  leachate collection systems  that  are equivalent  to

or more efficient than conventional granular systems may be used.  The following

criteria should be used to determine  equivalence:

     0  Design

          - hydraulic  transmissivity  (i.e., the amount of liquid that can
            be  removed);
          - compressibility (i.e., ability to withstand overburden pressure
            while remaining functional);
          - compatibility (mechanical) with the liners (i.e.  thin, low-
            modulus FML's in contact  with some drainage materials may
            distort under pressure);

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                                      48
           -  ability  to collect  leachate;
           -  compatibility with  leachate and waste;

      0   Construction method

      0   Operation/performance characteristics

           -  drainage or flow characteristics (i.e., how fast liquid will flow
             and what volume will flow)
           -  sensitivity to leakage/small leaks;
           -  time required for detection of leachate;
           -  ability  to verify performance ;
           -  reusability of the system once a leak is detected; and
           -  useful life of the system.

     An  owner/operator wishing to use an innovative collection system should

compare  the  properties of his design aqainst a conventional granular design

that uses  the recommended design specification [see Design (a),(b) and (c)].

If the alternative drain layer is equivalent, he may proceed;  if not, the

alternative design should be abandoned.  If one or more of the factors are

not equivalent, the collection system would probably not perform as well as

a conventional granular system and would be a source of constant trouble to

its owner/operator.

     If the owner or operator wishes to determine the source of liquids

found in the secondary collection system,  the fallowing records on the design,

operation, and closure of landfill and surface impoundment units may provide

useful information:

     0 Subsurface drilling logs including  seasonal ground-water
       elevations;

     0 "As-built" drawings,  certified by a professional engineer, for the
       double liners  and  collection system(s);

     0 Analytical data indicating the waste characteristics over time and
       the leachability of these constituents under site-specific conditions
       as included  in the  waste analysis plan;

     ° Accurate  tables and plots of measured primary (for landfills) and
       secondary leachate  collection system fluid volumes;

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                                      49
      0 Tables  and plots of monthly averages of data from primary and secondary
       leachate  analyses  (consistent parameters should be used);

      8 Construction quality assurance documentation report;

      0 Other supporting data; e.g., rainfall, terrperature, etc.; and

      0 An  explanation prepared during design to explain why observed leachate
       nay not be due to  a leak in the top liner.

      Additionally, EPA suggests that the owner/operator may determine that

simple statistical analyses (such as conparing the quality of liquids in the

leachate collection system to the quality in the leak detection system), may

be helpful in  developing  assessments of top liner integrity.  The use of tracers

to determine the extent of migration could also be used.

     The Agency believes that it is practical to operate a collection system

between two liners.   Sites are currently using these systems to monitor the

performance of the top liner.  The collection system allows the owner/operator

to detect,  collect,  and remove liquids in the secondary leachate collection

system.

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                                       50
                      IV.  Construction Quality Assurance


                                   Contents

                                                                      Page

   A.   Guidance --------------------------     59

          Objective	     50
          Design and Construction -----------------     51

   B.   Discussion  -------------------------    52
     A.  Guidance

     Overall Design, Construction, and Operation Objective

     All new surface impoundments and landfills, new units, lateral expansions,

and replacement units nust have at least tvo liners with a leachate collection

system betaken the liners (and above for landfills).  The double liners and

collection system(s) must be designed, constructed, and operated to protect

human health and the environment.  To assure that a completed double-liner

system meets or exceeds all projected design criteria, plans, and specifications,

a construction quality assurance (CQA) program is necessary.  In addition,

the regulations for permitted units (§§264.226 and 264.303) specifically

require liners to be inspected during construction for uniformity, damage,

and imperfections (e.g., holes, cracks, thin spots, or foreign materials);

immediately after construction EML's must be inspected to ensure tight seams

and joints, and the absence of tears, punctures, or blisters.

     As part of the CQA program for compacted soil liners, a test fill should

be constructed using the same material procedures and equipment that will be

used in the full scale facility.  The CQA plan to be followed during the

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                                       51
 full scale facility construction should be exactly followed during construction

 of the  test fill.

      Design and Construction

      (a) The owner/operator should sutnit and inplement a written construction

 quality assurance plan to be used during construction of the primary leachate

 collection system (for landfills), secondary leachate collection, and top

 and  composite bottom liners.  The plan should be used in monitoring and

 documenting the quality of materials used and the conditions and'manner of

 their placement.  The plan should be developed,  administered,  and documented

 by a registered professional civil or geotechnical engineer with experience

 in hazardous waste disposal facility construction and construction site

 inspections.  While the specific content of the construction quality assurance

plan will depend on site-specific factors,  the following specific components

 should be included,  at a minimum:

     0 Areas of responsibility and lines of authority in executing the CQA

       plan;

     0 Qualifications of GQA personnel;

     0 Specific observations,  and  tests  - preconstruction,  construction,  and

       post-construction tests  to  verify that materials and equipment will

       perform to specifications,  and that  the performance  of the individual

       parts of the double-liner system conform  to design specifications.

      As completed, the  individual parts of the double-liner installation

      should be tested for functional integrity.   The FML  joints,  seams,

      and  mechanical seals should be checked both during and  after installation.

      A variety of testing methods can  be  used  such  as:

         - hydrostatic
         - vacuum
         - ultrasonic
         - air jet
         - spark testing.

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                                       52
      In addition to hydraulic  conductivity  tests on undisturbed saitples




      taken from the conpacted  soil  layer during construction, the low-permeable




      soil layer should be tested  for  functional integrity through the use of




      field hydraulic conductivity testing on the conpleted soil layer when




      practical.   The collection layer(s) should be tested to assure the




      components  are functioning as designed.




    0  Sampling program design;  the frequency and scale of observations and




      tests,  acceptance-rejection  criteria,  corrective measures, and statistical




      evaluation.




    0  Documentation  of OQA should  include daily recordkeeping (observation




      and test data  sheets, problem reporting and corrective measures data




      sheets),  block evaluation reports for  large projects, design engineer




      acceptance reports  (for errors,  inconsistencies, and other problems),




      and final documentation.  After  completion of the double-liner system,




      a  final  documentation report should be prepared.  This report should




      include  summaries of all  construction  activities, observations, test




      data sheets, problem reports and corrective measures data sheets,




      deviations from design and material specifications, and as-built drawings.




      (b) The  documentation for the CQk program for the construction




of the unit should  be kept on-site in the facility operating record.




      B.  Discussion




     Construction quality assurance (OQA) during construction of the double-




liner system is essential to assure, with a reasonable degree of certainty,




that  the system meets the design specifications.  This involves inspecting




and documenting the quality of materials used and the construction practices




employed in their placement.  CQA serves to detect deviation from the design




caused by error or negligence on the part of the construction contractor,

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                                      53
 and to allow for  suitable corrective measures before wastes are disposed.

 Without proper  ccnstruction quality assurance, problems with the leachate

 collection system(s), and FML top and. conposite bottom liners due to construction

 may not be discovered until the system fails during operation.

     A recent survey of hazardous waste surface impoundment technology has

 found that rigorous quality assurance is necessary to achieve good unit

 performance  (Ghassemi, et al 1984).  Liner failures at several impoundments

 were attributed to various factors including "failure to execute proper

 quality assurance and control."  The success of surveyed facilities that have

 performed well is attributed to many factors including "the use of competent

 design,  construction, and inspection contractors,  close scrutiny of all

phases of design,  ccnstruction,  and QA inspection by the owner/operator,

excellent QA/QC and recordkeeping during all phases of the project, and good

cottttunications between all parties involved in constructing the units."

     Specific problems that can cause failure of the double-liner system and

that can be avoided with careful construction quality assurance include:

     Collection System(s)

     '" The use of materials other than those specified in the approved design;

     0 Foreign objects (e.g.,  soil)  left in drain pipes,  which plug or restrict
      flow and may not be  removable using currently available maintenance
      procedures;

     0 Neglecting  to install materials at locations specified in the design;

     0 Neglecting  to follow installation procedures specified in the design;

     0 Siltation of drainage material resulting from improper upgradient drainage
      during construction  and/or  careless construction techniques;

     0 Improper  use of construction  equipment causing crushing or misalignment
      of pipes;

     0 Improper  layout of the  system,  including misalignment of pipe joints
      or improper slopes and  elevation of pipes;  and

     0 Use of unwashed gravel  or sand in  drain layers.

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                                       54
      FML's Used as the Top Liner and as the Upper Component of the Composite
      Bottom Liner

      8 The use of materials other than those specified in the approved design;

      0 Inproper preparation of the supporting surface  (usually soil subgrade)
        to receive the liner;

      0 The use of improper installation techniques and procedures by the
        contractor;

      0 The improper use of construction tools and equipment;

      0 Inadequate sealing and anchoring of  the liner to structures, pipes,
        and other penetrations through the liner;

      0 Installation of the liner during inclement weather; and

      0 Improper repair of defects in the installed liner resulting from
        manufacturing processes and installation methods.

      Low Permeability Soil Layer in Composite Bottom Liner

      0  The use  of materials other than  those specified in the approved design;

      0  Improper compaction equipment;

      0  Inadequate compactive  effort;

      0  Inproper compaction procedures;

      0  Inadequate scarification between lifts;

      0  Excessive  lift  thickness;

      0  Inadequate liner thickness;

      0  Excessive  field hydraulic  conductivity;

      8  Inadequate method of water addition;

      8  Inadequate time allowed  for  even distribution of moisture;

      8  Inadequate method used to maintain the optimum moisture content in
       the liner between construction of each lift and after completion of
       the liner; and

      0 The use of an inadequate quantity of added  fine-grained materials
        (important with bentonite/soil liners).

     The ability of the hazardous waste disposal unit to meet its designed

regulatory performance goals depends on adherence  to approved design plans

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                                       55
 and specifications during construction.   Confidence  in the ability of the

 installed liners to perform properly is  attained through  a well-developed,

 well-implemented,  and well-documented CQA program.   The program should be

 developed by the design engineer,  who can focus  the  enphasis of quality

 assurance on those elements of the design that are critical to FML and low-

 permeable soil liner performance.   Inplementation of the  CQA program should

 include participation by the design engineer  in  resolving construction or

 design problems  that nay be identified during construction.  Timely identifi-

 cation of such problems during construction allows corrective measures to be

 taken before construction is completed and wastes are deposited.  Confidence

 in the liner is  established through:

      0  Careful documentation of:

           -  Construction scheduling,  conditions, and progress;

           -  Site inspections;

           -  Material/equipment  testing results and data verification; and

           -  As-built conditions.

      0  The owner/operator providing the  cpportuiiity  for review, inspection,
        and approval by appropriate regulatory and permitting agencies.

     Each of the elements  identified as  components of the written construction

quality assurance plan will  be described in detail in an upcoming document

on the  subject of construction quality assurance for hazardous waste land

disposal units entitled, Construction Quality Assurance for Hazardous

Waste Land Disposal Facilities.  The document will address the components

listed below:

     0 Low permeability soil  liners;

     0 Flexible membrane liners (FML's) or synthetic membrane liners;

     0 Dikes;

     0 Low permeability soil caps and cover systems;  and

     0 Leachate collection systems.

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                                       56
                                           uUubLL LiNLK
      The FML/compacted low permeability soil double liner design  consists,



 at a minimum,  of a primary leachate collection and removal  system (for landfills),



 an FML top liner designed,  operated,  and constructed of materials to prevent



 the migration  of any constituent into such liner  during the period the unit



 remains in operation (including any post-closure  monitoring period), a



 secondary leachate collection system,  and a bottom liner designed, operated,



 and constructed to prevent  the migration of any constituent through the



 liner during this period  (See Figure 7).   The bottom liner  should consist of



 compacted soil with a hydraulic conductivity of 1 X 10"^.   The liner should



 be of compacted low permeability soil materials rather than in-situ soil



 materials.   The liner thickness should be calculated using  the formulas and



 assumptions  set out in this section of the guidance and should be three feet



 thick at  a minimum.



      EPA  believes that this design  will protect human health and  the environment



 because if liquid appears between the liner,  the  compacted  soil clay bottom



 liner provides for removal of some  leachate by the leachate collection



 system and infiltration of the  remaining  leachate into the  liner.  The liner



 is  designed  to be of sufficient thickness to prevent migration during the



 period of facility operation,  including the post-closure monitoring period.



      Section 3004(o) (5) (B) provides that,  until the effective date of EPA



 regulations  implementing Section 3004 (o) (1)(A), the statutory requirement



 for two liners may be  satisfied by the  installation of a top liner designed,



operated,  and constructed of materials  to prevent the migration of any



constituent  into such  liner during the period the facility  remains in operation



 (including any post-closure monitoring period)  and a lower  liner  designed,



operated,  and constructed to prevent  the  migration of any constituent through

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            Materials
Graded Granular Filter Medium
Granular Drain Material
   (bedding)
Flexible Membrane Liner (FML)

Granular Drain Material
   (bedding)
 Low Permeability Soil, Compacted in Lifts
   (soil liner material)
   Note:   FML thickness > 45 mils
   recommended if liner is not
   covered within 3 months.
                                                               FIGURE 7
                                          SCHEMATIC PROFILE OF AN FML/COMPACTED SOIL
                                               DOUBLE LINER SYSTEM FOR A LANDFILL
          Dimensions and Specifications

6  Odo° ?.:•?<> ?  <> V
 Recommended Thickness > 6 in.
 Maximum Head on Top Liner = 12 in.
Recommended Thickness > 12 in.
Hydraulic Conductivity > IxlO"2 cm/sec

  ,	Drain Pipe	
                                          O
Recommended Thickness of FML > 30 mils (see note)
Recommended Thickness > 12 in.
Hydraulic Conductivity > 1x10 2 cm/sec
    	 Drain Pipe 	
                                           o
 Thickness Determined by Breakthrough Time
 Recommended Hydraulic Conductivity < IxlO'7 cm/sec
               Unsaturated Zone
                                                                                             l
                                                    /.        Saturated Zone         ///////
                                                    ////////////////////////////I
                                                                                                                 Nomenclature
                                                                                                   Solid Waste
                                                      Filter Medium
                                                       Primary Leachate Collection and
                                                         Removal System
                                                                                                   Top Liner (FML)
                                                       Secondary Leachate Collection and
                                                         Removal System
                                                      Bottom Liner (compacted low permeability soil)
                                                                                                    Native Soil Foundation/Subbase

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                                       53
 such liner during this period.  Section 3004(o)(5)(B) also provides that a




 lower liner shall be deemed to satisfy this requirement if it is constructed




 of at least a  3-foot thick layer of conpacted clay or other natural material




 with a permeability of no more than 1 x 10~^.




      The Agency's EML/coirpacted soil double liner design contains the performance




 standards  set  out in the statute.  The inportant difference between the Agency's




 design and the statutory interim standard is that three feet of reconpacted




 clay will  satisfy the statutory requirement, while three feet is the minimum




 recommended thickness in the Agency's design.  Until EPA issues regulations




 implementing the statute, EPA will accept a bottom liner design of three




 feet  of compacted clay or other natural material with a permeability of no




 more  than  1  x  1CT7.  However, the Agency believes that this bottom liner




 will not in  practice meet the requirement to prevent migration of any constituent




 through the  liner during the operational period.  EPA believes that owners




 and operators who wish to install a clay lower liner should consider three




 feet  as a  minimum thickness and use this guidance to determine the recoranendea




 thickness.



      In order to meet this performance standard, both the top and bottom




 liner should be chemically resistant to the waste and leachate managed at the




 unit.  In  addition,  these liners should be constructed of materials that




have appropriate properties and sufficient strength and thickness to prevent




both  structural and chemical failure caused by factors which include material




aging and the stresses of construction and operation.




     The top liner must be a FML material that meets the requirement that




constituents not migrate into the liner.  EPA's recommended bottom liner




design is:




      (1)  That  it consist of a minimum three feet of conpacted soil with a




         hydraulic conductivity of 1 X 10~7 cm/sec or less; and

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                                      59
       (2) That it be sufficiently tliick so as to prevent any constituent from



          migrating through the bottom of the conpacted soil liner prior to



          the end of the post-closure monitoring period.



 Until the effective date of regulations inpleinenting section 3004(o) (1) (A),



 EPA will accept a three foot bottom liner.   However,  EPA believes that in



 practice a bottom liner consisting of three feet of compacted soil with a



 hydraulic conductivity of 1X10"^ cm/sec will not meet the second standard



 listed above.  In the case of a saturated soil,  low effective porosity values



 may allow the early release of constituents.  In the case of an unsaturated



 soil,  capillary forces may draw constituents through the liner prior  to the



 end of the post-closure monitoring period.   Therefore,  EPA recomnends that



 an owner or operator who wishes to install a bottom compacted low permeability



 soil liner use this guidance to determine the thickness of the bottom liner.



     Methods tliat have been suggested for modifying a compacted soil  liner to



 weet the recommended standard are as  follows:



      (1)  Decrease its  permeability; and/or



      (2)  Increase its  thickness.



 Either of these ways of modifying the liner could theoretically result in a



 liner  that would prevent migration for the  combined active life and 30 year



 post-closure monitoring period of a facility (usually a total of 40-50 years).



 The Agency does not  discourage rigorous demonstrations  of compacted low



 permeability soil  liner designs that  would  meet  the recommended standard.



 The Agency has, however,  strong reservations concerning the likelihood that



 such a design is either economically  or technically feasible.   Some of the



 issues underlying these reservations  are  as  follow:



     (1) There are no  clear criteria  or techniques  available for making



breakthrough determinations.  While several  methodologies have been suggested,

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                                       60
 the Agency is not aware of any methods which have undergone rigorous field-



 verification testing.



      (2) It is not clear whether it would be economically feasible to construct



 a low permeability soil liner thick enough to prevent breakthrough for over



 40 years assuming adequate flow from the overlying landfill or surface impoundment



 to maintain continuous unsaturated (capillary) flow through the soil liner



 during that period.   Recent computer models of unsaturated flow through



 compacted liners suggest that assuming continuous flow through the liner,



 a liner may need to be much greater tlian 10 feet  thick even at hydraulic



 conductivities substantially less than 1 X 10~"7 on/sec.



      (3)  Hydraulic conductivities of 1 X 10"? cm/sec or  less have not been



 routinely and consistently obtained in the past on an overall  in-field scale



 liner system.   A number of studies have suggested that actual  field scale



 hydraulic conductivities may be  in the range of 10 to 1000 times higher than



 the  1 X 10~7  to 1 X 10~8 cm/sec  values that are routinely obtainable in



 laboratory tests.  The Agency believes that if a  testfill (described in the



 section on construction of low permeability soi\)  is used,  a hydraulic conductivity



 of 1X10~7  can be achieved in the liner.



      (4) The  capability of current testing methods to verify with a high



 degree  of  confidence the actual  field performance of a compacted low permeability



 soil  liner has not been demonstrated.   Consequently,  the  Agency currently



 believes that the  best  method would include construction  of a  test fill and the




 collection of  field hydraulic conductivity data.



     Test  fills have been used by the geotechnical engineering community to



 evaluate the design of  soil  liners used in cooling ponds  for the nuclear



power industry.  Test fills have also been used during the design stage of



dams to obtain information on engineering properties of  the compacted soil



such as density, strength, and hydraulic conductivity (Barren,  1977).   Construction

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                                       61
 control of test  fills  must be  very strict and well documented or the data
 obtained will be of questionable value  (Corps of Engineers, 1977).
      Field hydraulic conductivity tests have been found to give a much more
 accurate assessment of the hydraulic  conductivity of conpacted soil liners
 (Daniel, 1984; Day  1984).   Field tests conducted in a test fill should be an
 effective and accurate method  to predict the overall saturated hydraulic
 conductivity  of  a compacted soil liner.  Both test fills and field hydraulic
 conductivity  tests  are discussed in greater detail in Section II of this
 guidance document.
      The time required for liquid to  breakthrough a conpacted soil liner will,
 in most cases, be initially governed  by unsaturated liquid flow through the
 liner.   During the  early stages of wetting of a conpacted liner, capillary
 attraction forces predominate  over gravitational forces.  As a compacted
 liner becomes wetter,  the  capillary forces would decrease in importance.  In
 a saturated liner,  capillary forces are negligible in comparison to gravitational
 forces.
      To accurately  and reliably estimate the t^ae to breakthrough for a given
 liner thickness,  a  field verified equation is required that accounts for
 effective porosity,  water  content, capillary forces, and unsaturated hydraulic
 conductivity  at various depths in the liner over time.  Unsaturated hydraulic
 conductivity measurements  are both difficult and not routinely performed by
 soil engineering  laboratories.  The task of documenting unsaturated hydraulic
 conductivity  values  for a compacted low permeability soil liner at several
water contents would indeed be difficult on even a small laboratory scale.
 In addition,  the Agency is not aware  of any field scale studies to verify
 laboratory-derived unsaturated hydraulic conductivity values.

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                                       62
      The Agency is studying the  breakthrough of constituents  through compacted



 low permeability soil liners.  There  is  currently however, no field verified



 method for determining either  breakthrough or the associated  liner thickness



 requirements.   Using the draft computer  model which  is currently in development



 and as yet not field tested (SOILINER),  the  interim design (i.e., a three



 foot thick compacted liner  with  a  saturated  hydraulic conductivity of 1X1CT7



 cm/sec)  representing a landfill  scenario with a one foot head above the liner



 results  in a breakthrough time of  approximately three years (Johnson and



 Wood,  1984).   Assuming adequate  flow  from the overlying landfill or surface



 impoundment to maintain continuous unsaturated (capillary) flow through the



 soil liner during  the operating  and post-closure period, a compacted liner



 would  need to  be at  least several  times  this thickness or be  of a lower



 order  of permeability in  order to prevent breakthrough of mobile waste



 constituents during  the 40  to  50 years most  surface  impoundments and landfills



 will be operated,  including the  post-closure monitoring period.



     The draft computer model  discussed  above has been published by the EPA



 (1984B).   The Agency  plans  to  update  this model and evaluate  further the



 appropriateness of it for use  in estimating  the thickness requirements or



 breakthrough time for compacted  liners.



     Conservative assumptions  should  be used in estimating the compacted



 low permeability soil liner thickness because of the lack of  precision



with which  such estimates can  be made.  There are several difficult to



estimate variables that affect the thickness needed to prevent migration



of hazardous constituents over the operational life of the soil liner.



Examples of the conservative assumptions that should be used  to estimate




soil liner thickness are  as follows:

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                                       63
       1.  Breaches develop in the top FML during the first year of operation.



       Even with a rigorously implemented construction quality assurance plan,



 it  is not possible to be 100% certain'that all defects initially present  in



 the FML have been detected.  In addition, weak seams may open up shortly  after



 installation due to operational stresses (e.g., overburden pressures  that



 occur during the initial placement of wastes).  Equipment is more likely  to



 damage the FML shortly after installation because there may only be a leachate



 collection layer between the equipment and the liner.



      2.   The leakage/impingement rate of leachate to the soil liner should be



          based on an estimate of active life  and post-closure (for disposal



          units)  conditions.



      For landfills during the active life the leakage into the compacted



 soil liner should be based on the rate  of moisture/liquid infiltration into



 the  landfill considering (1)  leachate collection and removal by the primary



 leachate  collection system under proposed removal  conditions,  (2)  leachate



 leakage through potential top liner failure conditions,  (3)  leachate  collection



 and  removal  by the  secondary  leachate collection system,  and (4)  the  compacted



 soil liner surface  conditions.   Failure conditions  for the  top liner  should



 consider data from existing similar units currently in operation when available.



 The  failure  conditions should consider  all liner breaches  that may  be expected



 to occur during construction, active life, and  the  post-closure monitoring



period of the unit.  Even small  leaks in  the  FML could allow a  steady supply



of leachate to a portion of the compacted  soil  liner.  The  type of  failures



that should be considered  (i.e., seam failures, punctures,  rips, tears,



chemical  compatability) are addressed in  the  U.S. EPA Technical Resource



Docunent  Lining of Waste Impoundments and  Disposal  Facilities, SW-870, March 1983.

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                                       64
      If the owner  or  operator agrees  to repair breaches in the liner during



 operation or other time periods  then  repair can be  included as part of the



 calculation.   The  repair  assumptions  in the calculation should be representative



 of actual repair operating practices.



      Unless data is available to demonstrate that the top liner will have zero



 leakage throughout the operating life of the unit (including the post-closure



 monitoring period)  a  very small  leakage rate should be assumed to occur when



 leachate is in the primary leachate collection system.



      For surface iinpoundments during the active life the leakage rate  into



 the compacted  soil  liner  should  be based on (1) the maximum designed operating



 head  for the  impoundment, (2) leakage through potential top liner failure



 conditions,  (3) leachate  collection and removal by the secondary leachate



 collection system,  and (4) the compacted soil liner surface conditions.  The



 top liner failure conditions that should be considered are discussed above



 under landfills.



      During the post-closure monitoring period the leachate impinging on the



 primary  leachate collection system for a landfall or top liner in a surtace



 impoundment should  represent 1)  the effectivness of the final cover in minimizing



 precipitation  infiltration during the post-closure monitoring period and 2)



 drainage  from  the waste resulting from precipitation that was intercepted by



 the waste during the active life, and leachate that is generated from decornposit




of  the organic waste constituents.



      3.  The post-closure monitoring period should be at least 30 years.



      Current Subpart G requirements are for post-clsoure care to "continue for



 30 years after the  date of completing closure".  This time frame is considered



by EPA to be a minimum estimate of how long the waste will remain hazardous.

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                                       65
      4.  Leakage from potential top liner failure conditons would occur  throughout



          the operation period unless the owner or operator agrees to repair the



          breaches.



      As discussed in assumption Number 2, there are several ways leachate  can



 form during the operational period of the unit.



      5.  Nature and quantity of the waste should be considered.



      Volume of leachate released by the waste as deconposition by-products



 will depend on the total organic content of the waste.   The higher the organic



 content of a waste,  the greater would be the fraction of the waste which



 could be liquify during its deconposition.   The total quantity of organic



 materials in the facility would affect the  total volume  of leachate that



 could eventually be  generated fron deconposition of the  waste.



      Composition of  a waste will affect the conposition  of the leachate.



 High concentrations  of  certain leachate ccnponents may increase  the rate at



 which a soil liner transmits leachate (Anderson, 1982).   If the  leachate



 has  a flow  rate  through the compact soil liner faster than water this should



 also be considered in the evaluation of required liner thickness.



      6.   Any allowance  for attenuation of the waste constituents by the  soil



          liner should take into account the nature of the waste  and any  factors



          that may reduce  attenuation.



     Some waste  constituents (such as  cations)  can be strongly attenuated  by-



soils under  ideal conditions (EPA/  1983C).   The effect is difficult to quantify



but may be considered in  limited  cases such as some monofills.  The demons tr a tic,-



of acceptability should be based on data from field tests.   The  extent to



which many of these  are attenuated  can,  however,  be greatly decreased in the



acidic and anaerobic conditions that are often present near soil liners.



Other waste constituents  (such  as anions) may not be  appreciably attenuated

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                                       66
 by soil.  Movement of waste constituents will also  be  affected by the effective



 porosity of the soil liner.  There are a number of  other  conditions under



 which attenuation can be greatly reduced.   In addition, the conditions that



 optimize attenuation of one constituent  may promote leaching of another



 (Lindsey, 1979).




        7.  The effective porosity would  be  0.05.




      Total porosity of a compacted soil  will  usually be less than 0.5 (Anderson



 et al.,  1984;  and Brown and Anderson,  1983).   Effective porosity can be much



 less  than total porosity in fine-grained soils (Gibb et al., 1985).  Green



 et al,  (1985)  found that in some  compacted  samples only 10% of the total



 porosity was effective  in transmitting liquids.  Ten percent of even the



 highest  total  porosity  likely in  a compacted  specimen would result in an



 effective porosity  of no greater than 0.05.




      8.   The compacted  low permeability  soil  liner  and adjacent soil strata



          would be  initially  unsaturated.



      Design criteria given  elsewhere in  this document state that the liner



 system for the two designs should be construct^ completely above the seasonal



 high water table  (i.e.,  in unsaturated soil).   Under these conditions, the



 soil strata immediately adjacent to the  liner would probably also be unsaturated.





The owner/operator should fully document methods used to evaluate the necessary



liner thickness.  These evaluations should also address at least the following:



     (1)  Horizontal hydraulic conductivity within and between the individual




         lifts (Brown et al, 1983 Boynton, 1983);



     (2)  Variability in the  hydraulic conductivity of the compacted soil



         liner in  the field  (Daniel, 1984);



     (3)  The potential for long term changes in hydraulic conductivity



         resulting from loss of moisture by the liner due to climatic conditions

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                                       67
          or the equilibrium moisture content in the adjacent soil deposits;  and



      (4) The effect of liner aging on the long-term equilibrium hydraulic



          conductivity of the liner (Mitchell et al, 1965;  Dunn and Mitchell



          (1984); Boynton, 1983).



      Under this approach to bottom liner design,  the leachate collection and



 removal system between the two liners must be:  (1)  capable of detecting,



 collecting, and removing liquids  in case leaks  develop in  the primary liner,



 (2)  constructed of materials that can withstand the chemical attack that



 results from wastes or leachates, (3) capable of withstanding the stresses



 and  disturbances from overlyinq wastes and operating practices,  and (4)



 operated to collect and remove liquids through  the  operating period,  including



 the  post-closure monitoring period.



     The collection system between the two liners  should comply with the



 guidance contained in Section III of  the Synthetic/Composite Double Liner



 System.   For landfills,  the leachate  collection and removal system above the



 top  liner should  comply  with the  guidance contained in Section I of the



 Synthetic/Composite  Double  Liner  System.   The t-'.p liner should comply



 with the  guidance  contained in section II.   The bottom liner should comply



 with the  relevant  portions  of  section II  dealing  with the  compacted lower



 component of the composite  liner.  Section IV,  on Construction Quality Assurance,.



 should  be used to  assure  that  the  completed  double  liner system  meets the



design criteria and specifications.

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                                       68
                                   References

 Anderson, D.C. (1982), Clay Liner-Hazardous Waste Conpatibility.  Report to
   the U.S. EPA, K.W. Brown and Associates,  College Station, Texas.   (EPA
   Contract # 68-01-6515)

 Anderson, D.C., J.O. Sai, and A.  Gill (1984),  Surface  Impoundment Soil
   Liners:  Permeability and Morphology of a Soil  Liner Permeated by Acid and
   Field Permeability Testing for Soil Liners.   Report  to U.S. EPA, K.W.
   Brown and Associates, College Station,  Texas.   (EPA  Contract  # 68-03-2943)

 August,  H.,  R. Tatzky, G. Pastuska,  and T.  Wift. (1984),  Study of the Permeation
   Behavior of Commercial Plastic Sealing  Sheets as a Bottom Liner for Dumps
   Report No.  103  02 208, Federal  Minister of the  Interior, Berlirr, West Germany.

 Barren,  R.A.  (1977),  The Design of Earth  Dams.  (Chapter 6) In  (A.R. Golze,
   ed) Handbook of Dam Engineering. Van Nostrand Reinhold Company, N.Y. p.
   291-318.

 Boutwell,  G.P. and V.R. Donald (1982),  Compacted  Clay Liners for Industrial Waste
   Disposal, Presented ASCE National  Meeting, Las  Vegas, April 26, 1982.

 Boynton,  S.S.  (1983),  An Investigation of Selected Factors Affecting the
   Hydraulic Conductivity of Compacted Clay.  M.S.  Thesis, University of
   Texas,  Geotechnical Engineering Thesis  GT83-4,  Geotechnical Engineering
   Center, Austin,  Texas.  79 p.

 Boynton,  S.S.  and D.E.  Daniel  (1985), Questions Concerning Hydraulic Conductivity
   of  Compacted Clay.   Journal of Geotechnical Engineering, Vol. Ill, No. 4.

 Brown, K.W. and D.C. Anderson.  (1983), Effects of Organic Solvents on the
   Permeability of  Clay Soils.  United States Enviromental Protection Agency.
   Grant No. R806825010.   153 p.

 Brown, K.W., J.W.  Green,  and J.C. Thomas,  J.C.  (1983),  The Influence of Selected
   Organic Liquids  on the  Permeability of Clay Liners,  In Proceedings of
   the Ninth Annual Research Symposium on Land Disposal of Hazardous Waste,
   (EPA-600/9-83-018). p.  114-125.

 Corps of Engineers  (1977), Earth-fill and Rock-fill Construction.  (Chapter 5)
   In Construction Control for Earth and Rock-Fill Dams.  U.S. Arny Engineer
  Manual EMI 110-2-1911

Daniel, D.E. (1984), Predicting Hydraulic Conductivity of Clay Liners.
  Journal of Geotechnical Engineering, Vol.  110, No. 2  p. 285-300.

Daniel, D.E.,  D.C. Anderson and S.S.  Boynton  (1985), Fixed-Wall vs Flexible-Wall
  Permeameters. _In Hydraulic Barriers in Soil and Rock,  ASTM STP 874 (In
  Press).

Day,  S.R. (1984),  A Field Permeability Test for Compacted Clay Liners.  M.S.
  Thesis, University of Texas,  Austin, Texas 105 p.

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                                       69
  Day, S.R.,  D.E. Daniel, and S.S. Boyriton, (1985), "Field Permeability Test
    for Clay  Liners.  In Hydraulic Barriers in Soil and Rock,  ASTM STP 874
    (In Press).

  Dunn, R.J.  and J.K. Mitchell  (1984), Fluid Conductivity Testing of Fine-Grained
    Soils.  Journal of Geotechnical Engineering, Vol. 110,  No. 11, p. 1648-1665.

  Earth Manual. (1984), Bureau of Reclamation, U.S. Department of the Interior.
    Government Printing Office, Washington, D.C.

  EPA  (1982), Test Methods for Evaluating Solid Waste.  United States Environmental
    Protection Agency, Washington, D.C.  (SW-846).

  EPA  (1983), Landfill and Surface Impoundment Performance Evaluation United
    States Environmental Protection Agency/ Washington,  D.C.  (SW-869), April 1983.
    (S/N 055-000-00233-9,  $5.00), Superintendent of Documents, U.S.  Government
    Printing Office,  Washington, D.C. 20402, 69 pages.

 EPA  (1983A), Lining of Waste Impoundment and Disposal  Facilities.   United States
   Environmental Protection Agency,  Washington, D.C.  (SW-870),  March 1983.
    (S/N 055-000-66231-2,  §11.00), Superintendent of Documents, U.S. Government
   Printing Office,  Washington, D.C. 20402, 448 pages.

 EPA (1984B), Procedures  for Modeling Flow Through Clay Liners to Determine
   Required Liner Thickness.  (Draft Technical Resource Document for Public
   Comment)  United States Environmental Protection Agency, Washington,  D.C.
   (EPA/530-SW-84-001).  32 p.

 EPA (1984A), Soil Properties,  Classification,  and Hydraulic  Conductivity
   Testing.   United  States Environmental Protection Agency, Washington,  D.C.
   (SW-925).  167  p.

 EPA (1983C), Hazardous Waste Land Treatment,   f'.iited States  Environmental
   Protection Agency, Washington,  D.C.   (SW-874).

 Geotextile Engineering Manual,  Training Manual, Federal Highway Administration.

 Ghassemi, M., M. Haro, and  L.  Fargo (1984),  Assessment of Hazardous Waste
   Surface Impoundment Technology Case  Studies  and Perspective of Experts.
   Report to  the U.S. EPA, MEESA,  Torrance, CA.  (EPA Contract #69-02-3174),

 Green, J.W., K.W. Brown, J.D.  Thomas  (1985), Effective Porosity of Compacted
   Clay Soils Permeated with Organic Chemicals.  _In Land Disposal of Hazardous
   Waste, Proceedings of  the Eleventh Annual  Research Synposium,  pp.  270-271.

Griffin, R.A. et al. (1984), Migration of Industrial Chemicals  and Soil-waste
   Interactions at Wilsonville,  Illinois.  _In_ Proceedings of  the Tenth Annual
   Research Symposium on Land Disposal  of  Hazardous  Waste  (EPA 600/9-84—007)
   USEPA Municipal Environmental Research  Laboratory, Cincinnati, OH 45268.

Griffin, R.A., N.F.  Shrimp, Attenuation of Pollutants  in Municipal Landfill
  Leachate by Clay Minerals, EPA-600/2-78-157, U.S.  EPA, MERL,  Cincinnati, OH
   [OTIS PB 287-140/AS].

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                               D/TF HUE
                                      70
 Griffin, R.A., R.E. Hughes, L.R. Polluter, C.J. Stohr,  W.J.  Morse,  T.M.  Johnson,
   J.K. Bartz, J.D. Steele, K. Cartwright, M.M. Killey and P.B.  DuMontelle
   (1984), Migration of Industrial Chemicals and Soil-Waste Interactions at
   Wilsonville, Illinois.  In:  Proceedings of the Tenth Annual  Research
   Symposium on Land Disposal of Hazardous Waste, (EPA 600/9-84-007)'.

 Herzog, B.L. and W.J.  Morse (1984), A Corrparison of Laboratory  and Field
   Determined Values of Hydraulic Conductivity at a Waste Disposal  Site.   In:
   Proceedings of the Seventh Annual Madison Waste Conference, University of
   Wisconsin-Extension, Madison,  Wisconsin, pp 30-52.

 Horz, R.C.  (1984), Geotextiles for Drainage and Erosion Control at Hazardous Waste
   Landfills.  EPA Interagency Agreement No. AD-96-F-1-400-1.  U.S. EPA,
   Cincinnati,  Ohio.

 Johnson,  Russell and Eric Wood,  (1984),  Unsaturated Flow Through Clay Liners.
   Report to the U.S. EPA,  GCA Corporation, Bedford., MA.  (EPA Contract
   #68-01-6871).

 Johnson,  Russell and Eric Wood,  (1984),  Unsaturated Flow Through Clay Liners
   (Letter Report).  Prepared for the Office of Solid Waste, Washington,  D.C.,
   GCA Corporation, Bedford,  NA.   (GCA-TR-85-01-G)  29 p.

 Kays,  W.B.  (1977), Construction  of Linings For Reservoirs, Tanks,  and Pollution
   Control Facilities.  John Wiley & Sons,  Inc.  NY.  379 p.

 Koerner,  Robert M., and J.P. Welsh (1980),  Construction  and Geotechnical Engineering
   Using Synthetic Fabrics.   John Wiley and Sons, New York.

 Lindsey,  W.L.   (1979), Chemical  Equilibria in Soils.   John Wiley and  Sons,  Inc.,
   449 p.

 Mitchell, J.K.  (1976), Fundamentals of Soil Behavior.  John Wiley arid  Sons,
   Inc., N.Y. 422p.

 Mitchell, J.K., D.R. Hooper, and R.G. Canpanella (1965), Permeability of
   Compacted Clay.  Journal of the Soil Mechanics and Foundations Division,
   ASCE, Vol. 91, No. SM4. p. 41-65.

NSF (1983),  Standard Number  54, Flexible Membrane Liners.  National Sanitation
   Foundation, Ann Arbor, Michigan.  69p.
                                    ?
Olson, R.E.  and D.E. Daniel  (1981), Field and Laboratory Measurement  of  the
  Permeability of Saturated and Partially Saturated Fine-Grained Soils.   .In
  Permeability and Groundwater Contaminant  Transport, ASTM STP  746.
            U.S. Environmental Protection Agency
            Region V, Library
            230 South Dearborn Street
            Chicago, Illinois  60604            ;

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                                        71
                               Suggested Reading List


 Flexible Membrane Liner Permeation

 Haxo, H. E.,  J.  A. Miedema,  and N. A.  Nelson  (1984),  Permeability of Polymeric
 Membrane Lining Materials for Waste  Management Facilities.  In Proceedings
 of the Education Symposium on Migration of Gas, Liquids, and Solids in Elastomers,
 Denver, Colorado.  Sponsored by Rubber Division, American Chemical Society,
 Oct.  23-26,  1984.

 August, H.,  R.  Tatzky,  G.  Pastuska,  and T. Win (1984), Study of the Permeation
 Behavior of  Commercial  Plastic Sealing Sheets  as a Bottom Liner for Dumps
 Against Leachate, Organic Solvents,  and their  Aqueous Solutions.  Research
 Report No. 103  02 208,  Federal Minister of the Interior, Berlin, West Germany.

 Mitchell, J.  K.,  D.  R.  Hooper,  and R.  G. Campanella,  (1965), Permeability of
 Compacted Clay.   Journal  of  Soil Mechanics Foundation Division, ASCE, 91 (SM4):
 41-65.

 Statistical earthwork control

 Hinterkorn, H.,  and H.  Y.  Fang.  Foundation Engineering Handbook, Van-Nostrand-
 Reinhold, Publishers (1975),  See Chapter 7 by  Jack W. Hilf, section 7.4:
 Control of Compaction.

 Lee,  I. K., W. W-iite, and O.  G.  Ingles.  Geotechnical Engineering, Pitman Publishers
 (1983),  See Chapter  2,  Soil Variability; and Chapter 9, Soil Treatment:
 Quality Assurance.  (Good  general introduction  to the use of statistics).

 Representative samples

 U.S.  Environmental Protection Agency.  Test  Methods for the Evaluation of
 Solid Waste.  SW-846, Washington, D.C., July 1982 Second Edition.

 U.S.  Environmental Protection Agency.   Draft Solid Waste Leaching Procedure
 Manual.  Washington,  D.C., 1983.

 Graded  granular filters

 U.S.  Environmental Protection Agency.  Guide to the RCRA Land Disposal Permit
 Writers' Training Program, Volume 1, Sept. 1984, Chapter 3, p.  3-38 to 3-41.

 Synthetic fabric  filters

U.S.  Environmental Protection Agency.  Guide to the RCRA Land Disposal Permit
Writers's Training Program, Volume 1, Sept., 1984, Chapter 3, p.  3-44 to 3-46.

 U.S. Federal Highway Administration.  Geotextile Engineering Manual.

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