&EPA
          United States
          Environmental Protection
          Agency
          Technology Transfer
                    EPA/625/4-89/022
Seminar Publication

Requirements for
Hazardous Waste Landfill
Design, Construction, and
Closure

-------

-------
Technology Transfer
EPA/625/4-89/022
Seminar Publication

Requirements for Hazardous
Waste Landfill  Design,
Construction, and Closure
August 1989
Center for Environmental Research Information
Office of Research and Development
U.S. Environmental Protectin Agency
Cincinnati, OH 45268

-------
                                 NOTICE
The information in this document has been funded wholly or in part by the United States
Environmental Protection Agency under Contract 68-C8-0011 to  Eastern Research
Group, Inc. It has been subject to the Agency's peer and administrative review, and it has
been approved for publication as an EPA document. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.

-------
                               CONTENTS
                                                                        Page
   Preface	 vi

1.  Overview of Minimum Technology Guidance and
   Regulations for Hazardous Waste Landfills	  1
     Background	  1
     Double Liners and Leachate Collection and
       Removal Systems	  2
     Leak Detection Systems	  6
     Closure and Final Cover	  9
     Construction Quality Assurance 	  9
     Summary of Minimum Technology Requirements	   10
     References  	   10

2.  Liner Design: Clay Liners 	   11
     Introduction	   11
     Materials 	   11
     Clay Liners versus Composite Liners 	   12
     Darcy's Law, Dispersion, and Diffusion	   13
     Laboratory Tests for Hydraulic Conductivity  	   17
     Field Hydraulic Conductivity Testing 	   20
     Field Tests versus Laboratory Tests	   23
     Attack by Waste Leachate  	   24
     References	   26

3.  Flexible Membrane Liners	   27
     Introduction	   27
     Composite Liners: Clay versus Synthetic Components  	   27
     Material Considerations	   27
     Design Elements	   30
     References  	   39

4.  Elements of Liquid Management at Waste Containment Sites	   53
     Introduction  	   53
     Overview  	   53
     Primary Leachate Collection and Removal (PLCR) Systems 	   57
     Leak Detection, Collection, and Removal (LDCR) Systems  	   62
     Surface Water Collection and Removal (SWCR) Systems 	   65
     Gas Collector and Removal Systems  	   66
     References  	   70

5.  Securing a Completed Landfill	   75
     Introduction  	   75
     Flexible Membrane Caps  	   75
     Surface Water Collection and Removal Systems  	   75
     Gas Control Layer	,	   75
     Biotic Barriers	   78
     Vegetative Layer	   73
     Other Considerations  	   81

                                     iii

-------
6.  Construction, Quality Assurance, and Control:
   Construction of Clay Liners  	•	• •  39
     Introduction 	• •  °9
     Compaction Variables	• •  °9
     The Construction Process  	;• •  94
     Construction Quality Assurance (CQA) Testing  	i.  95
     Test Fills	;• •  96

7.  Construction of Flexible Membrane Liners  	• •  99
     Introduction 	• •  99
     Responsibility and Authority  	'• •  "
     CQA Personnel Qualifications   	.•  10"
     Inspection Activities  	  100
     Sampling Strategies  	•  101
     Documentation  	•	•  103

8. Liner Compatibility with Wastes	••  109
     Introduction	•  1(^9
     Exposure Chamber 	•  1°9
     Representative Leachate  	•
     Compatibility Testing of Components	•
     Blanket Approvals 	
     Interpreting Data 	

9. Long-Term Considerations: Problem Areas and Unknowns  	,.  113
     Introduction 	
     Flexible Membrane Liners 	•
     Clay Liners 	•, •
     Leachate Collection and Removal Systems	:•
     Cap/Closure Systems	.•••'•

10. Leak Response Action Plans	: •
     Background  	• •
     Action Leakage Rate (ALR)	• •	• •
     Rapid and Large Leakage (RLL)	  122
     Response Action Plans (RAPs)	......;.  124
     Preparing and Submitting the RAP	• • •  124
     Summary  	•	f •  125

    List of Abbreviations 	•	  127
                                       IV

-------
                        ACKNOWLEDGEMENTS
This  seminar publication is  based wholly on  presentations  made  at  the  U.S.
Environmental  Protection Agency (EPA) Technology  Transfer seminars  on
Requirements for Hazardous Waste Landfill Design, Construction, and Closure. These
seminars were held from June 20 to September 16, 1988 in San Francisco, California;
Seattle, Washington;  Dallas, Texas; Chicago, Illinois;  Denver, Colorado;  Kansas  Cityi
Missouri; Philadelphia, Pennsylvania; Atlanta, Georgia; New  York,  New York; and
Boston, Massachusetts. The presenters were:

     Sarah A. Hokanson, the  Earth Technology Corporation, Alexandria, Virginia
     (Chapters 1 and 10)

     Dr. David Daniel, University of Texas, Austin, Texas (Chapters 2 and 6)

     Dr. Gregory N.  Richardson, Soil & Materials Engineers, Inc.,  Raleigh, North
     Carolina (Chapters 3, 5, and 7).

     Dr. Robert M.  Koerner,  Drexel University, Geosynthetic Research Institute,
     Philadelphia, Pennsylvania (Chapters 4 and 9).

     Robert Landreth, U.S. Environmental Protection Agency, Risk Reduction
     Engineering Laboratory, Cincinnati, Ohio (Chapter 8)

Susan Edwards, Linda Saunders,  and Heidi Schultz of Eastern Research Group,  Inc.,
Arlington, Massachusetts, prepared the text of this document based on the  speakers'
transcripts and slides. Orville  Macomber (EPA Center for Environmental Research
Information, Cincinnati, Ohio) provided substantive guidance and review.

-------
                                  PREFACE
The U.S. Environmental Protection Agency's (EPA's) minimum technological require-
ments for hazardous waste landfill design were set forth by Congress in the 1984 Hazard-
ous and Solid Waste Amendments (HSWA). HSWA covered requirements for landfill lin-
ers and leachate collection and removal systems, as well as leak detection  systems for
landfills, surface impoundments, and waste piles. In response to HSWA and other Con-
gressional mandates, EPA has issued proposed regulations and guidance on the design of
these systems, and on construction quality assurance, final cover, and response action
plans for responding to landfill leaks.

This seminar publication outlines in detail the provisions  of the minimum technology
guidance and proposed regulations, and offers practical and detailed information on the
construction of hazardous waste facilities that comply with these requirements. Chapter
One presents a broad overview of the minimum technology guidance and regulations.
Chapter Two describes the use of clay liners in hazardous waste landfills, including the
selection and testing of materials for the clay component of double liner systems. Chap-
ter Three discusses material and design considerations for flexible membrane liners, and
the impact of the proposed regulations on these considerations. Chapter Four presents an
overview of the three parts of a liquid management system, including the leachate collec-
tion and removal system; the secondary leak detection, collection, and removal system;
and the surface water collection system. Chapter Five describes the elements of a closure
system for a completed landfill, including flexible membrane caps, surface water collec-
tion and removal systems, gas control layers, biotic barriers, and vegetative top covers.
Chapters Six and Seven discuss the construction, quality assurance, and control criteria
for clay liners and flexible membrane liners, respectively.  Chapter Eight discusses the
chemical compatibility of geosynthetic and natural liner materials with waste ileachates.
Chapter Nine presents  an overview of long-term considerations regarding hazardous
waste landfills,  surface impoundments, and waste piles, including flexible membrane
and clay liner durability, potential problems in liquid management systems, and aesthet-
ic concerns.  Chapter Ten reviews proposed requirements for response action plans for
leaks in hazardous waste landfills.

This publication is not a design manual nor does it include all of the latest knowledge
concerning hazardous waste landfill design and construction; additional sources should
be consulted for more detailed information. Some of these useful sources can bei located in
the reference sections at the end of several chapters.  In addition, State and local authori-
ties should be contacted for regulations and good management practices applicable to lo-
cal areas.
                                        VI

-------
          1.  OVERVIEW OF MINIMUM TECHNOLOGY GUIDANCE AND
              REGULATIONS FOR HAZARDOUS WASTE LANDFILLS
 This chapter presents a summary of existing and
 proposed regulations and guidance on the design of
 double liners and leachate collection and removal
 systems, leak detection systems, final cover, and
 construction quality assurance. An overview  of
 proposed  regulations  concerning leak response
 action plans is given in Chapter Ten. More technical
 discussion of these and  other components of landfill
 design and construction are given in Chapters Two
 through Nine.

 Background
 EPA's minimum technological requirements for
 hazardous waste landfill design and construction
 were introduced by Congress in the 1984 Hazardous
 and Solid  Waste Amendments (HSWA). In HSWA
 Section 3004(o)(l)(A), Congress required all new
 landfills and surface impoundments to have double
 liners and leachate collection and removal systems
 (LCRS). In Section 3004(o)(4), Congress also required
 leak detection systems at all new land disposal units,
 including  landfills,  surface  impoundments, and
 waste piles. In response to  other Congressional
 mandates, EPA has  issued proposed regulations or
 guidance on the design of these systems. In addition,
 EPA has issued guidance on construction quality
 assurance programs and final  cover. While not
 specified in HSWA, the guidance and regulations in
 the additional  areas were  issued by  the  U.S.
 Environmental Protection Agency (EPA)  to ensure
 protection of human health and the environment.

 For these new hazardous waste landfills and surface
 impoundments, EPA and Congress have set  forth
performance objectives of preventing hazardous
constituent migration out of a unit through the end
of post-closure care (or approximately 30 to 50 years).
The approach EPA  has developed to  meet  those
performance objectives is  called  the Liquids
Management Strategy. The goal of the strategy is to
 minimize  leachate  generation  through  both
operational practices and the final cover design, and
to maximize leachate collection and removal through
use of the lining system and LCRS.

To date, EPA has issued regulations and guidance
primarily  focusing on double liners and leachate
collection and removal systems. Four Federal
Register notices and guidance documents  have been
published  by EPA in the last 4 years in this area (see
Table 1-1). EPA has issued proposed  regulations
and/or guidance in  the additional areas listed in
Table 1-2. The  draft guidance on the final cover
issued  in July  1982,  which was never widely
distributed, is being revised for reissuance  by the end
of 1989. EPA also plans to issue final regulations for.
double  liners and  for  leak  detection  systems,
including construction quality  assurance and
response action plans.
Table 1-1.  Guidance and Regulations Issued to Date
         (Double Liners and LCRS)


 • Codification Rule (July 15, 1985)
 • Draft Minimum Technology Guidance (May 24, 1985)
 • Proposed Rule (March 28, 1986)
 • Notice of Availability of Information and Request for Comments
   (April 17, 1987)
Table 1-2. Guidance and Regulations Issued to Date
        (Additional Areas)
 Leak Detection Systems
 • Proposed Rule (May 29, 1987)
 Construction Quality Assurance
 • Proposed Rule (May 29, 1987)
 • Technical Guidance Document (October 1986)
 Response Action Plan
 • Proposed Rule (May 29, 1987)
 Cover Design
 • Draft Guidance (July 1982)

-------
Double Liners and  Leachate Collection
and Removal Systems
Figure 1-1 is a simplified schematic diagram of a
hazardous waste landfill, showing the geometry and
placement of double liners and LCRSs in a landfill.
In a double-lined landfill, there are two liners and
two LCRSs. The primary LCRS is located above the
top liner, and the secondary LCRS is located between
the two liners.  In this diagram, the top  liner is a
flexible membrane liner (FML) and the bottom liner
is a composite  liner system consisting of a FML
overlying compacted  low  permeability soil (or
compacted clay).


Existing (Draft) Guidance for Double
Liners
The EPA draft guidance  issued in July 1985
discusses three types of liners: flexible  membrane
liners (FMLs); compacted clay liners; and composite
liner systems (a FML overlying a compacted low
permeability soil layer). Material  specifications in
the guidance for FMLs and compacted clay liners are
briefly reviewed below, along with existing and
proposed regulations  regarding all three liner
systems.

The minimum thickness specification for a FML top
liner covered with a layer of soil is 30 mils; for a FML
without a soil cover layer,  the specification is  45
mils. A FML in a composite  bottom liner system
must be  at least 30 mils thick. Even though these
FML thicknesses meet EPA specifications, 30 mils is
not a suitable thickness for all FML materials. In
fact, most FML materials installed at landfills are in
the range of 60 to 100 mils  in thickness. Other key
factors affecting selection of FML materials include
chemical compatibility with waste leachate, aging
and durability characteristics, stress and strain
characteristics, ease of installation,  and  water
vapor/chemical permeation. These factors  are
discussed in greater detail in Chapter Three.

For compacted, low permeability soil liners, the EPA
draft guidance recommends natural soil materials,
such as clays and silts. However,  soils amended or
blended with different additives (e.g., lime, cement,
bentonite clays, borrow clays) also may  meet the
current selection  criteria of low  hydraulic
conductivity,  or permeability,  and sufficient
thickness   to  prevent hazardous constituent
migration out of the landfill unit. Therefore, EPA
does not currently exclude compacted soil liners that
contain these amendments. Additional factors
affecting the design and construction of compacted
clay liners include plasticity index, Atterburg limits,
grain  sizes, clay mineralogy,  and attenuation
properties. These factors are discussed further in
Chapter Two.
Existing and Proposed Federal
Regulations for Double Liners
Figure 1-2 shows cross sections of three double liner
designs that have  been used to; meet existing or
proposed regulations. The double liner design on the
left side of the figure meets the existing minimum
technological requirements (MTR) as codified in July
1985. The center and right-hand designs meet the
MTR as proposed  by EPA in March  1986.  The
existing regulations for MTR call for a double liner
system consisting of a FML top liner  and a
compacted clay bottom liner that is 3 feet thick and
has a maximum saturated hydraulic conductivity of
no more than 1 x 10-7 centimeters per second
(cm/sec). The 1986  proposed rule on double liners
gives two design options for MTR  landfills: one
similar to the existing MTR design (differing only in
that the compacted clay liner must be sufficiently
thick to prevent  hazardous  constituent migration);
and one calling for a FML top  liner and composite
bottom liner.                   ',

EPA is currently  leaning toward requiring a
composite bottom  liner in the' final  rule to be
published in the summer of 1989. The Agency also is
considering allowing use of a composite liner as an
optional top liner system, instead of a FML. The final
rule, however, probably will not have  minimum
thickness or  maximum hydraulic conductivity
standards  associated with the compacted clay
component of such a composite top liner.

EPA's rationale for favoring the; composite bottom
liner option in the  final double liner rule would be
based on the relative permeability of the two liner
systems. Figures 1-3 through 1-5 show the results of
numerical  simulations performed by EPA (April
1987) that compare the performance of a composite
bottom liner to that of a compacted soil bottom liner
under various  top liner leakage scenarios. In these
scenarios, liquids pass through defects in the top
FML and enter the secondary' LCRS above  the
bottom liners. As  illustrated  in these  numerical
results, the hydraulic conductivities of these  bottom
liner systems greatly  affect the amounts of liquids
detected, collected, and removed by  the secondary
LCRS.

Figure 1-3 compares  the compacted  soil and
composite bottom liner  systems  in terms  of
theoretical leak detection sensitivity, or the minimal
leak rate  that  can be detected,  collected, and
effectively removed in the secondary  LCRS. The
theoretical leak detection sensitivity is  less than 1
gallon per acre per day (gal/acre/day) for a composite
liner having an  intact FML component. This leak
detection sensitivity  value reflects water vapor
transmission rates for  FMLs  with no defects. In
contrast, with well-constructed clay bottom liners

-------
                                   Double Liners and Leachate Collection System

                                            Components
                         - Protective Soil or
                           Cover (Optional)
                                                  r- Top Liner (FML)
                                         — Drain Pipe (Typ)
                                                 Solid Waste
                                     .  .  ,•';'. Drainage '•;.'. '•!•.•'•' : • .•'. ' • •.•'./'•':•.'•..'
                                  '•'•' '• '• •: 'o'.' Material   'Q . '. •. •.'. :.•'.;''.  .' Q ' '•'  ', '-"•
  Leachate Collection
  and Removal System
Leachate Detection,   .
Collection, and
Removal System (LDCRS)
.' • • j •••:••.•.••".. Drainage • • •'. •••.••';.'.•'.••••••  •. •
V'. • .'* '.!>'• ^/v. Material  :.n  • •>'.•»'• n'-'.'. '4'.  .'•.•'
>>.  •     • o.	.	w •   . • • u      . i  . •
    Compacted Low-Permeability Soil
                                      Native Soil Foundation
                                                                   ,"- 3'
Source: EMCON, 1988

Figure 1-1.  Schematic of a double liner and leachate collection system for a landfill.
Bottom
Composite Liner
Upper Component
(FML)
Lower Component
(compacted soil)
                                                     Leachate Collection
                                                     System Sump
                                                     (Monitoring Compliance
                                                     Point)
      cm/sec permeability), liquids entering the
secondary LCRS may go undetected and migrate into
the bottom liner until the leak rates approach 100
gal/acre/day. With a slightly more permeable
compacted  clay bottom liner with  10-6 cm/sec
permeability, the secondary LCRS'may not detect,
collect, or remove the  liquid flowing from a leak in
the top liner until leak rates are very serious (on the
order of 1,000 gal/acre/day).

Figure 1-4 compares theoretical leachate collection
efficiencies for landfills having compacted soil
bottom liners with those having composite bottom
liners. Leachate collection efficiency is the amount of
liquid collected and  removed in the secondary
leachate collection system divided by the total
amount entering into the secondary LCRS through a
breach in the top liner.  For low leakage rates, the
leachate collection efficiency  of a landfill with a
composite bottom liner  system, even a composite
system with tears or small defects in the FML, is
very high (above 95 percent for leak rates in the
range of 1  to  10  gal/acre/day).  In  comparison,
landfills with compacted clay bottom liners have 0
percent leachate collection  efficiency  for low leak
rates, and only 50 percent efficiency for leak rates of
approximately 100 gal/acre/day. These results
demonstrate that leachate collection efficiency of the
secondary LCRS improves significantly simply  by
                       installing a FML over the compacted clay bottom
                       liner.

                       Figure  1-5  shows  the total quantity of liquids
                       entering the two bottom liner systems over a 10-year
                       time span with a constant top liner leak rate of 50
                       gal/acre/day. A composite bottom liner with an intact
                       FML accumulates  around 70  gal/acre, primarily
                       through water vapor transmission. Even with a 10-
                       foot  tear, which would  constitute a worst-case
                       leakage scenario, a composite liner system will allow
                       47,000 to 50,000 gal/acre to enter that bottom liner
                       over a 10-year  time span.  Compacted soil liners
                       meeting the 10-7 cm/sec permeability standard will
                       allow significant quantities of liquids into the bottom
                       liner, and potentially out of the unit over time, on the
                       order of hundreds of thousands of gallons per acre.

                       The numerical results indicate superior performance
                       of composite liner systems over compacted clay liners
                       in preventing hazardous constituent migration out of
                       the unit and maximizing leachate collection and
                       removal. Consequently, many owners of new units
                       subject to the double liner requirement of HSWA are
                       proposing and installing composite bottom liners or
                       double composite liner systems, even though they
                       are not required currently. A survey conducted in
                       February of 1987 and revised in November of that
                       year has indicated that over 97 percent of these MTR

-------
landfills and  surface impoundments have one  of
these two double liner designs.
Existing (Draft) Guidance for Leachate
Collection and Removal Systems
Double-lined landfills  have both primary  and
secondary LCRS. The design of the secondary LCRS
in the landfill receives particular attention in EPA's
proposed leak detection requirements. Described
below are the  existing guidance and  proposed
regulations applicable to both LCRSs in double-lined
landfills.

The components of a LCRS  include the drainage
layer, filters,  cushions,  sumps,  and pipes  and
appurtenances. Of these  components, the drainage
layer receives the most attention in the guidance and
regulations. The drainage layer can consist of either
granular or synthetic material. If granular,  it must
be either clean sand or gravel with very little fines
content in order to facilitate the rapid collection and
removal of the liquids that accumulate above the top
liner and between the two liners. This minimizes
hydraulic head on both liner systems.
                                 According to the draft guidance, the main selection
                                 criteria for granular  drainage materials are high
                                 hydraulic conductivity and low capillary tension, or
                                 suction forces. Figure 1-6 shows a range of hydraulic
                                 conductivities for natural granular materials. For
                                 typical drainage layer materials, permeabilities
                                 range between 10-3 cm/sec and 1 cm/sec. A silty sand
                                 drainage layer with significant fines  content  will
                                 have a lower permeability (i.e., liO-3  cm/sec)  and
                                 significant capillary tension. At the-upper end of the
                                 scale, drainage layers consisting of plean gravel can
                                 achieve a permeability on the order of 1 cm/sec to 100
                                 cm/sec. In this upper range of permeability, capillary
                                 tension is  negligible. Therefore clean sands  and
                                 gravels are preferred over silty sands.

                                 Table  1-3 shows the correlation  between
                                 permeability and capillary rise (the elevation height
                                 of liquids retained by granular particles within the
                                 drainage layer by surface tension under unsaturated
                                 conditions). At 10'3  cm/sec,  there  is significant
                                 capillary rise (approximately 1 meter) while at the
                                 upper  end of the permeability scale  (1 cm/sec), the
                                 capillary rise  is only  on the  order of an inch.
                                 Reduction in fines content, therefore,  significantly
                                 reduces capillary rise while increasing hydraulic
        Interim
    Statutory Design
                                                            Proposed Designs
          Waste
    Leachate Collection
     System Between
         Liners
                     Design 1

                     Waste
  O
o
         3 Feet
                Leachate Collection
                 System Between
                     Liners
                                                          Design 2

                                                          Waste
O
O
        Native Soil
                                      Native Soil
                                Top Liner
                          Designed, Constructed, and
                            Operated to Prevent
                           Migration—AL & PCCP
                                          Bottom Liner

                                            Composite
                                    Upper Component Prevent (FML)
                                    Lower Component Minimize (clay)

                                         Compacted Soil
                                        Sufficient Thickness
                                   *    to Prevent Migration
                                        During AL & PCCP
   Leachate Collection  '
   : System Between
        Liners
o :	     o
                                                                                        Native Soil
 Figure 1-2. Interim statutory and proposed double liner designs.

-------
  1000
   800
1
o
 0
 c
 Q.
 O
I-


 o> 600
 o
 CO
oc
 §* 400
^
 co
 CD
 O
 CD
Q
E
3
E
'E
i
   200
               860
           Compacted Soil
         k = 1 x 1 o-6 cm/sec
                           86
                                    0.001
Compacted Soil
k = 1 x 1 0-7 cm/sec

Composite
(intact)
                                                       100
                     Type of Bottom Liner

 Source: 52 FR 12570, April 17, 1987

 Figure 1-3. Comparison of leak detection sensitivities for 3-
          foot compacted soil and composite liners (one-
          dimensional flow calculations).
conductivity. Increasing hydraulic conductivity, in
turn, results in rapid collection  and removal of
liquids.

Synthetic drainage, materials-have-only recently
been introduced to^the wasfe management industry.
Unlike granular materials,  synthetic drainage
materials come in various forms and thicknesses:

• Nets (160-280 mils)

• Needle-punched nonwoven geotextiles (80-200
  mils)

• Mats (400-800 mils)

• Corrugated, waffled, or alveolate plates (400-800
  mils)
                                                        50
                                                     o
                                                     O

                                                     I
                                                     I
                                                     CD
                • Composite
                  (intact)

             • Composite with
             Small FML Hole
                                                                 Compacted Soil  -.
                                                              k = 1  x 10'7 cm/sec
                                                                                          11 Compacted Soil
                                                                                          = 1 x 10-6 cm/sec
      1        10        100      1,000      10,000
            Top Liner Leakage Rate (gal/acre/day)

Source: 52 FR 12572, April 17, 1987

Figure 1-4.  Comparison of leachate collection efficiencies
          for compacted soil and composite bottom liners.
                                                     Construction materials also vary. The most common
                                                     synthetic materials are polypropylene, polyester, or
                                                     polyethylene.  More detailed discussion of these
                                                     drainage materials is presented in Chapter Four.
                                                     Because synthetic drainage layers are much thinner
                                                     (less than 1 inch) than granular drainage layers (1
                                                     foot) and have similar design liquids capacity, their
                                                     use in a landfill results in increased space for waste
                                                     storage and disposal. This advantage translates into
                                                     increased revenues fo"f"the owner/operator of a
                                                    -landfill.	

                                                     The main selection criteria for  synthetic drainage
                                                     materials are  high hydraulic transmissivities, or
                                                     inplane flow rates, and chemical compatibility with
                                                     the waste  leachate.  Discussion of chemical
                                                     compatibility of synthetic liners and drainage layers
                                                     is given in Chapter Eight.

                                                     Hydraulic transmissivity  refers to the value of the
                                                     thickness  times the hydraulic conductivity for that
                                                     drainage layer. Over the  lifetime of af facility, the
                                                     actual hydraulic transmissivities of synthetic
                                                     drainage layers are affected by two key  factors: (1)
                                                     overburden stress and (2)  boundary conditions. The
                                                     first factor pertains to the increasing  loads (i.e.,

-------
   200.000
la
   150,000
£ 100,000
   50,000
               160,000
             Compacted Soil
           k = 1 x 10'7 cm/sec
47,000
                    Type of Bottom Liner

Source: 52 FR 12574 , April 17, 1987

Figure 1-5.   Cumulative 10-year leakage into the bottom
           liner for a leak of 50 gal/acre/day through the
           side wall of the top liner.
Table 1-3.  Capillary Rise as a Function of the Hydraulic
         Conductivity of Granular Materials
   Hydraulic Conductivity of
     Drainage Medium (k)
         cm/sec
    Capillary Rise (h)
         in
         1 x 10-3
         1 x 10-2
         1
        38.6
        12.2
         1.2
Source: EPA, May 1987


wastes, operating equipment, and final cover)
applied to the liner that an LCRS experiences over
the lifetime of the facility. The second factor pertains
to the stress-strain characteristics of adjacent layers
(i.e., PMLs, filters, cushions, compacted clay). Over
time and with increasing stress, adjacent layers will
intrude,  or extrude, into the drainage layer and
result in clogging, or reduced transmissivity, of the
LCRS.                        '

Proposed Regulations for Leachaie
Collection and Removal Systems
Proposed regulations applicable tp LCRSs in double-
lined landfills  (March 1986) differ in two principal
ways from  existing  standards for LCRS in single-
lined landfills and waste piles. First, LCRSs must be
designed to operate through the end of the post-
closure care period (30 to 50 years), and not simply
through the active life of the unit. Secondly, in a
double-lined landfill with primary and secondary
LCRSs, the primary  LCRS need only cover the
bottom of  the unit (i.e.,  sidewall coverage  is
optional). The secondary LCRS, hbwever, must cover
both the bottom and the side walls.

As in the existing standards for single-lined landfills
and waste  piles, the  proposed regulations also
require that LCRSs be chemically resistant to waste
and leachate, have sufficient strength and thickness
to meet design  criteria, and be able  to function
without clogging.              ;

Applicability of Double Liner and LCRS
Requirements
According to HSWA Section 3004,(o)(l), all new units
(landfills and  surface impoundments)  and lateral
expansions or replacements of;existing units for
which permit applications were submitted after
November 8,1984 (the date  HSWA was enacted) will
be required to comply with these double-liner and
LCRS requirements once they are finalized. If permit
applications for  these units were submitted  before
this date, new  units need not have double liners and
LCRSs unless the applications were modified after
the date HSWA was enacted. However, EPA can use
the omnibus provision of HSWA to  require  double
liners and LCRSs that meet the liner guidance on a
case-by-case basis at  new facilities, regardless  of
when the permit applications were submitted. Table
1-4 identifies facilities  that will be  required  to
comply with the new regulations.

Leak Detection Systems
Described in this section are proposed leak detection
system requirements  that  apply to the secondary
LCRS between the  two liners  in a landfill. These
requirements focus on the drainage layer component
of the LCRS. Figure 1-7 illustrates the  location of a
leak detection system in a double-lined landfill that
meets these requirements.      ;

Proposed Design Criteria <
The proposed minimum  design standards for
granular  drainage  layer materials require a
minimum  thickness  of 1  foot and  a minimum

-------
Table 1-4. Landfills and Surface Impoundments Subject to
         Proposed Regulations

                APPLICABLE UNITS
            Permit Applications Submitted
Before 11/8/84
New Facilities
If permit
modified after
11.8.84:
Interim Status
Facilities
If permit modified
after 11/8/84:
Permitted Facilities
New units at
previously Interim
Status facilities
No
Yes
No
Yes
No*
After 11/8/84
New Facilities
Interim Status
Facilities
Existing units:
New units
(operational)
after 5/8/85):
Permitted Facilities
New units at
previously Interim
Status facilities:
yes
No
Yes
Yes
'Proposing to require MTR for these units on site-by-site basis.

hydraulic conductivity of 1 cm/sec. In order to meet
this proposed  minimum hydraulic conductivity
standard for  granular  drainage  materials, the
secondary LCRS, or leak detection system, must be
constructed of clean gravels.

For synthetic drainage materials, EPA has proposed
a minimum hydraulic transmissivity of 5 x  1O4
square meters  per second (m2/sec).  The hydraulic
transmissivity of a drainage  material refers to the
thickness of the drainage layer multiplied by the
hydraulic conductivity. The  transmissivity of
                            granular drainage layers (1 foot x 1 cm/sec) is within
                            an order of magnitude of the 5 x 1O4 m2/sec standard
                            for synthetic drainage  layers.  The proposed
                            hydraulic transmissivity  value  for synthetic
                            drainage materials was developed to ensure that the
                            design performance for a geonet, geocomposite, or
                            other synthetic drainage layer is comparable to that
                            for a 1-foot thick granular drainage layer.

                            The proposed standards for leak detection systems
                            also specify a minimum bottom slope of 2 percent, as
                            is recommended in the existing draft guidance for
                            LCRS,  and  require  the installation of  a  leak
                            detection  sump of appropriate size to  allow  daily
                            monitoring of liquid levels or inflow  rates in the leak
                            detection  system. Specifically, the sump should be
                            designed to  detect a top liner leakage  rate in the
                            range of the action leakage rate (ALR) specified in
                            the proposed leak detection  rule. Chapter Ten
                            discusses the proposed ALR in more detail.
                            Proposed Design Performance
                            Requirements
                            The proposed leak detection rule also establishes
                            design performance standards for the leak detection
                            system. Design performance standards mean that
                            the facility design  must  include materials  and
                            systems that can meet the above-mentioned design
                            criteria. If the liners and LCRS materials meet the
                            design criteria, then  the design  performance
                            standards will be met. Compliance  with design
                            performance standards can be demonstrated through
                                    Coefficient of Permeability (Hydraulic Conductivity) in CM/SEC
                                                     (Log Scale)
                   102
   101
                                    1.0
                                                    10-2
                                     10-3
                                                                      10-4
                                   ID'5
                                                               10-6
                                                    10-7
        Drainage
        Potential
                    Good
                                                      Poor
                                              Almost
                                             Impervious
          Soil
         Types
Clean gravel
Clean sands, and
clean sand and
gravel mixtures
Very fine sands, organic
and inorganic silts, mixtures
of sand, silt and clay, glacial
till, stratified clay deposits,
etc.
 Adapted from Terzaghi and Peck (1967)

 Figure 1-6. Hydraulic conductivities of granular material!;.

-------
                                  1 -ft Granular Drainage Layer

                                     Compacted Soil
     2% min '.'•••'•i''•.:••:•;: •:•"•
MfeMtfMYfHNnwWWVv*"**9** " _ • . * « • *
;. •.';';; •' :•'.••'. •\'\'•:•'.'•'• /•' 2% min  •;'•';
                                                                   Protective Soil Cover

                                                                   Leachate Collection and
                                                                   Removal System (above top liner)
                                                                —- Top Liner (Composite)
Leachate Detection, ;
Collection, and Removal System
                                                                —  Bottom Liner (Composite)
                  t granular drainage layer
                     (k > 1 cm/sec)
        - 3-ft min compacted soil
          (k < 1  x 10-7 cm/sec)
                       Legend

                       Geotextile
                       (synthetic fibers—woven, nonwoven or knit)
                       Geonet
                       (plastics formed into an open, netlike
                       configuration (used here in a redundant manner))
                       Flexible Membrane Liner (FML)
 Figure 1-7.  Location of a leak detection system in a double-lined landfill that meets proposed requirements.
numerical calculations rather than through field
demonstrations.

The proposed leak detection rule outlines two design
performance  standards:  (1)  a leak detection
sensitivity of 1 gal/acre/day and (2) a leak detection
time of 24 hours. The leak detection sensitivity refers
to the  minimum top  liner leak  rate  that  can
theoretically be detected, collected, and removed by
the leak detection system. The leak detection time is
the  minimum time needed for liquids  passing
through the top liner to be detected, collected, and
removed in the nearest downgradient collection pipe.
In the case of a composite top liner, the leak detection
time refers to the period starting at the point when
liquids have  passed through the compacted soil
component and ending when they are collected in the
collection pipe.

EPA bases its 1  gal/acre/day  leak  detection
sensitivity on the results of calculations that show
that, theoretically, a leak detection system overlying
a  composite  bottom liner with an intact  FML
component can detect,  collect, and  remove liquids
                 from a top liner leak rate less .than 1 gal/acre/day
                 (see Figure 1-3). This  performance standard,
                 therefore, can be  met with designs that include a
                 composite bottom liner. Based on numerical studies,
                 one cannot meet the leak detection sensitivity with a
                 compacted soil bottom  liner,  even  one with a
                 hydraulic conductivity of 10-7 cm/sec. Therefore, the
                 emphasis of this standard  is on selecting an
                 appropriate bottom liner system.

                 Meeting the 24-hour leak detection time, however, is
                 dependent on the design of the leak detection system.
                 A drainage layer meeting the design criteria,
                 together  with  adequate  drain spacing,  can
                 theoretically meet  the  24-hour detection  time
                 standard. The emphasis of the proposed standards,
                 therefore, is on  designing and  selecting appropriate
                 materials for the secondary LCRS.

                 As stated  previously, compliance  with EPA's
                 proposed design  performance  standards  can be
                 demonstrated through one-dimensional, steady-state
                 flow calculations, instead of field tests.  For detection
                 sensitivity,  the calculation of flow  rates should

-------
assume uniform top  liner leakage.  For detection
time, factors such as drain spacing, drainage media,
bottom slope, and top and bottom liners should all be
considered,  and the  worst-case leakage scenario
calculated.

Applicability  of Leak Detection System
Requirements
Owners  and operators  of landfills,  surface
impoundments, and waste piles  on  which
construction begins 6  months after the date the rule
is finalized will be required to install double liners
and leak detection systems.

Closure and  Final Cover
The following section  reviews existing guidance and
regulations concerning the  design .of the final cover
on top of closed landfills. EPA is' currently revising
the guidance for final covers. The  recommended
design differs little from that contained in the July
1982 draft version, with the exception that  some of
the design values for  components  of the final cover
have been upgraded. EPA plans to issue the revised
guidance for final covers in 1989.

Draft Guidance and Existing Regulatory
Requirements
EPA issued regulations and  draft  guidance
concerning  closure and final cover for hazardous
waste facilities  in  July  1982. Basically, the
regulations require that the final  cover be no more
permeable than the liner system. In addition, the
cover must be designed to  function with minimum
maintenance, and to  accommodate settlement and
subsidence of the underlying waste. The regulations
do not specify any design criteria for liner materials
to meet the performance standard for permeability.

The draft guidance issued in July  1982 recommends
a three-layer cap design consisting of a vegetative
top cover, a middle drainage layer, and a composite
liner system composed of a FML over compacted low
permeability soil. The final  cover is to be placed over
each cell as it is completed.

Since the regulations  do  not specify designs  of
materials for the final cover, or cap, design engineers
can usually use their own judgment in designing the
final cover and selecting materials. For example, if
the lining system  contains a high density
polyethylene (HOPE) membrane, the final cover does
not necessarily need to have a HOPE membrane. The
amount of flexibility in selecting FML materials for
the final cover varies from region to region, based on
how strictly'the statutory phrase  "no more
permeable than" is interpreted. Nevertheless, from a
design perspective, the selection of FML materials in
the final cover should emphasize the physical rather
than the chemical properties of the liner material,
since the main objective is to minimize precipitation
infiltration. Precipitation infiltration is affected
mainly by the number of holes or tears in the liner,
hot by the water vapor transmission rates.

For  the  vegetative  cover, EPA's  guidance
recommends a minimum thickness of 2 feet and final
upper slopes of between 3 and 5 percent, after taking
into account total settlement and subsidence of the
waste.  The middle drainage layer should have a
minimum thickness of  1  foot and minimum
hydraulic conductivity of 10-3 cm/sec. EPA's revised
draft guidance upgrades that standard by an order of
magnitude to 10-2 cm/sec to reduce capillary rise and
hydraulic head above the composite liner system. For
the composite liner system at the bottom of the cap, it
is critical that both the FML and the compacted soil
components be below the average depth of frost
penetration. The FML should also have a minimum
thickness of 20  mils, but 20 mils will not be a
sufficient thickness for all  FML materials. The soil
component under the FML must  have  a minimum
thickness of 2 feet  and  a  maximum saturated
hydraulic conductivity of 10-7 cm/sec. The final upper
slope of the composite liner system must be no less
than  2 percent after settlement.  Table 1-5
summarizes specifications for each part of the final
cover.


Construction Quality Assurance
The final component of the regulatory/guidance
summary discusses construction of a hazardous
waste landfill.  The following section summarizes
EPA's construction quality assurance  (CQA)
program, as it is presented in existing guidance
(October 1986) and proposed regulations (May 1987).
Chapter Seven contains a more detailed discussion of
CQA implementation.


Guidance and Proposed Regulations
The  proposed regulations  and existing  CQA
guidance require the  owner/operator to develop a
CQA plan that will be implemented by contracted,
third-party engineers. The owner/operator also must
submit a CQA report containing the following:

• Summary of all observations, daily inspec-
  tion/photo/video logs.

• Problem  identification/corrective  measures
  report.

• Design engineer's acceptance reports (for errors,
  inconsistencies).

» Deviations   from  design  and  material
  specifications (with justifying documentation).

-------
 Table 1-5. Cover Design
 Vegetative Cover
 • Thickness 2: 2 ft
 • Minimal erosion and maintenance (e.g., fertilization, irrigation)
 • Vegetative root growth not to extend below 2 ft
 • Final top slope between 3 and 5% after settlement or
   subsidence. Slopes greater than 5% not to exceed 2.0
   tons/acre erosion (USDA Universal Soil Loss Equation)
 • Surface drainage system capable of conducting run-off across
   cap without rills and gullies

 Drainage Layer Design
 • Thickness > 1 ft
 • Saturated hydraulic conductivity > 10-3 cm/sec
 • Bottom slope > 2% (after settlement/subsidence)
 • Overlain  by graded granular or synthetic filter to prevent
   clogging
 • Allow lateral flow and discharge of liquids

 Low Permeability Liner Design
 FML Component.
 • Thickness > 20 mil
 • Final upper slope > 2% (after settlement)
 •   Located, wholly below the average depth of frost
     penetration in the area
 Soil Component.
 • Thickness a 2 ft
 • Saturated hydraulic conductivity < 1 x 10-7 cm/sec

 • installed in 6-in lifts
•  Summary of CQA activities for each landfill
   component.

This report  must  be signed by a registered
professional engineer or the equivalent, the CQA
officer, the design engineer, and the owner/operator
to ensure that all parties  are  satisfied with the
design and construction of the  landfill. EPA will
review selected CQA reports.

The CQA plan covers  all components of landfill
construction, including  foundations, liners,  dikes,
leachate collection and  removal systems, and final
cover. According to the proposed rule  (May  1987),
EPA also may require field permeability testing of
soils on a test fill constructed prior to construction of
the landfill to verify that the final soil liner will meet
the permeability standards of 10-"7 cm/sec. This
requirement, however, will not preclude the  use of
laboratory  permeability  tests and  other  tests
(correlated to  the field permeability tests) to verify
that the soil liner  will, as  installed, have a
permeability of 10-7 cm/sec.
Summary of Minimum Technology
Requirements
EPA's minimum  technology ; guidance  and
regulations for new hazardous waste land disposal
facilities emphasize the importance of proper design
and construction in the performance of the facility.
The current trend in the regulatory programs is to
develop standards  and recommend designs based on
the current state-of-the-art technology. Innovations
in technology are,  therefore, welcomed by EPA and
are taken into account when developing these
regulations and guidance.

References
1.  EMCON Associates.  1988.  Draft background
    document on the final double liner and leachate
    collection system rule. Prepared for Office of
    Solid Waste, U.S. EPA. NUS Contract No. 68-01-
    7310, Work Assignment No. 66.

2.  U.S. EPA. 1987a. Liners and leak detection for
    hazardous waste land disposal units: notice of
    proposed rulemaking. Fed. Regi Vol 52, No.  103,
    20218-20311. May 29.         :

3.  U.S. EPA. 1987b. Hazardous waste management
    systems: minimum technology  requirements:
    notice of availability of information and request
    for comments.  Fed. Reg. Vol. 52, No. 74, 12566-
    12575. April 17.

4.  U.S.  EPA.  1987c. Background document on
    proposed liner and leak detection rule. EPA/530-
    SW-87-015.                  :

5.  U.S. EPA. 1986a. Technical guidance document:
    construction quality assurance  for hazardous
    waste land disposal facilities. EPA/530-SW-86-
    031.

6.  U.S. EPA. 1986b. Hazardous waste management
    systems: proposed codification rule. Fed. Reg.
    Vol. 51, No. 60,10706-10723. March 28.

7.  U.S. EPA. 1985a. Hazardous waste management
    systems:  proposed codification rule. Fed. Reg.
    Vol. 50, No. 135, 28702-28755. July 15.

8.  U.S. EPA. 1985b. Draft minimum technology
    guidance on double liner systems  for landfills
    and  surface  impoundments  -  design,
    construction, and operation. EPA/530-SW-84-
    014. May 24.

9.  U.S. EPA. 1982. Handbook for remedial action at
    waste  disposal  sites.  EPA-625/6-82-006.
    Cincinnati, OH: U.S. EPA.
                                                 10

-------
                            2.  LINER DESIGN: CLAY LINERS
Introduction
This chapter discusses soil liners and their use in
hazardous waste  landfills. The chapter focuses
primarily on hydraulic conductivity testing, both in
the laboratory and in  the field.  It also covers
materials used to construct soil liners, mechanisms
of contaminant transport through soil liners, and the
effects of chemicals  and waste  leachates on
compacted soil liners.

Materials
Clay
Clay is the most important component of soil liners
because the clay fraction of the soil ensures low
hydraulic   conductivity.   In   the   United
States.however, there is some ambiguity in defining
the term "clay"  because two soil  classification
systems are widely used. One.system, published by
the American  Society of Testing and Materials
(ASTM),  is used predominantly by civil engineers.
The other, the U.S. Department of Agriculture's
(USDA's) soil classification system, is used primarily
by soil scientists, agronomists, and soil physicists.

The distinction between various particle sizes differs
between ASTM and USDA soil classification systems
(see Table 2-1). In the ASTM system, for example
sand-sized particles are defined as those able to pass
a No. 4 sieve but not able to pass a  No. 200  sieve,
fixing a grain size of between 0.075 millimeters (mm)
and 4.74 mm. The USDA soil classification system
specifies a grain size for sand between 0.050 mm and
2mm.

The USDA classification system is  based entirely
upon grain size and uses a three-part diagram to
classify all soils (see Figure 2-1). The  ASTM system,
however, does not have a grain size criterion for
classifications of clay; clay is distinguished from silt
entirely upon plasticity criteria. The ASTM
classification system uses a plasticity diagram and a
sloping line, called the "A" line (see  Figure 2-2) to
distinguish between silt and clay. Soils whose data
 Table 2-1. ASTM and USDA Soil Classification by Grain Size

                       ASTM            USDA
      Gravel
       Sand
        Silt
       Clay
     4.74
  (No. 4 Sieve)

     0.075
 (No. 200 Sieve)

     None
(Plasticity Criterion)
                                       0.050
                                       0.002
points plot above the A line on this classification
chart are, by definition, clay soils with prefixes C in
Unified Soil Classification System symbol. Soils
whose data points plot below the A line are classified
as silts.

EPA requires that soil liners be built so that the
hydraulic conductivity is equal to or less than 1  x
10-7 cm/sec. To meet this requirement,  certain
characteristics of soil materials should be met. First,
the soil should have at least 20 percent fines (fine silt
and clay sized particles). Some soils with less than 20
percent fines will have  hydraulic conductivities
below 10-7 cm/sec, but at such low fines content, the
required  hydraulic  conductivity value is  much
harder to meet.

Second, plasticity index (PI) should be greater than
10 percent. Soils with very high PI, greater than 30
to 40 percent, are sticky and, therefore, difficult to
work with in the field. When high PI soils are dry,
they form hard clumps that are difficult to break
down during compaction. On the Gulf Coast of Texas,
for example, clay soils are predominantly highly
plastic clays and  require additional .processing
during construction. Figure 2-3 represents  a
collection of data from the  University of Texas
laboratory in Austin showing hydraulic conductivity
as a function of plasticity  index. Each data  point
represents a separate soil compacted  in the
                                                11

-------
                    Clay Loam \Silty Clay\^
            Sandy y\x—*
          ClayLoairf ^^	^
                    Percent Sand

 Figure 2-1. USDA soil classification.


laboratory with standard Proctor  compaction
procedures and  at a water content about 0 to 2
percent wet of optimum. Hydraulic conductivities
are consistently below 10-7 cm/sec for soils with Pis
greater than 10 percent.

Third,  coarse fragments should be screened to no
more than about 10  percent gravel-size particles.
Soils with a greater percentage of coarse fragments
can contain zones of gravel that have high hydraulic
conductivities.

Finally, the material should contain no soil particles
or chunks of rock larger than 1 to  2 inches in
diameter. If rock diameter becomes a significant
percentage of the thickness of a layer  of soil, rocks
may form a permeable "window" through a layer. As
long as rock size is small compared to the thickness
of the soil layer, the  rock will be surrounded by the
other materials in the soil.

Blended Soils
Due to a lack of naturally occurring soils at a site, it
is sometimes necessary to blend  imported clay
minerals with onsite soils to achieve a suitable
blended material. The most  common blend is a
combination of onsite sandy materials and imported
sodium bentonite.

Figure 2-4 shows the influence of sodium bentonite
on the hydraulic conductivity of the silt/sand soil.
The addition of only 4 or 5 percent sodium bentonite
 to  this particular soil  drops the hydraulic
  conductivity from 10-4 to 10-"7  cm/sec, a rather
  dramatic reduction.
                                 i
  Calcium  bentonite, though more permeable than
  sodium bentonite, has also been used for soil blends.
  Approximately twice as much calcium bentonite
  typically is needed, however, to achieve a hydraulic
  conductivity comparable to that of sodium bentonite.
  One problem with using sodium bentonite, however,
  is its vulnerability to attack by chemicals and waste
  leachates, a problem that will be discussed later in
  the chapter.

  Onsite sandy soils also can be blended with other
  clay soils available in the area, biit natural clay soil
  is likely  to form chunks that are difficult to break
  down into small pieces. Bentonites, obtained in dry,
  powdered forms, are much easier tjo blend with onsite
  sandy soils than are  wet, sticky clods of clay.
  Materials other than bentonite can be used, such as
  atapulgite, a clay mineral that is insensitive to
  attack by waste. Soils also can !be amended  with
  lime, cement, or other additives.  ;
  Clay Liners versus Composite Liners
  Composite liner systems should 'outperform either
  flexible membrane liners (FMLs) or clay liners alone.
  Leachate lying on top of a clay liner will percolate
  down through the liner at a rate controlled by the
  hydraulic conductivity of the liner, the head of the
  leachate on top of the liner, and the liner's total area.
  With the addition of a FML placed directly on top of
  the clay and sealed up against its upper surface,
  leachate moving down through a hole or defect in the
  FML does not spread out between the FML and the
  clay liner (see  Figure 2-5).  The  composite liner
  system allows much less leakage .than a clay liner
  acting alone, because the area of flow through the
  clay liner is much smaller.       '

  The FML must be placed on. top of the clay such that
  liquid does not spread along the interface between
  the FML and the clay and move downward through
  the entire area of the clay liner. A FML placed on a
  bed of sand, geotextiles,  or other highly permeable
  materials, would allow liquid to move through the
  defect in the FML, spread over the whole area of the
  clay liner, and percolate down as if the FML was not
  there (see Figure 2-6). With clay  liner soils that
  contain some  rock, it is sometimes proposed that a
  woven geotextile be placed, on  top of the soil liner
  under the FML to prevent the ipuncture of rocks
  through the FML. A woven geotextile between the
  FML  and the clay, however, ^creates a  highly
  transmissive zone between the FML and the clay.
  The surface of the soil  liner instead should be
  f compacted and the stones removed so that the FML
  can be placed directly on top of the clay.
12

-------
  JO
  CL
50
40
30
20
10
7
4
0
C
For classification of fine-grained soils
and fine-grained fraction of coarse-grained
soils.
Equation of "A" - Line
Horizontal at PI =4 to LL = 25.5,
then PI = 0.73 (LL - 20)
Equation of "U" - line
Vertical at LL = 1 6 to PI = 7,
then PI = 0.9 (LL - 8)

/.
yf s
S///, CL - ML
X I i
/
X
X
X

;-^^

/
X
/
. *
ov
S^
ML o

/
/
X
X
nv ^/
X
rOL
/•
*

/


/
X
^ S

MHc

X
-£j^


rOH


/




X





r





10 16 20 30 40 50 60 70 80 90 100 111
                                              Liquid Limit (LL)
 Figure 2-2. ASTM plasticity determination for fine-grained soils.
   o
   O
   g
       10-6
       10-7
       TO'8
       10-9
      10-10
                                   Upper Bound
                  • Lower Bound
                    	i
         10      20      30      40
                      Plasticity Index (%)
50
       60
 Figure 2-3.  Hydraulic conductivity as a function of plasticity
           index for soils in Austin Laboratory Tests.
Darcy's Law, Dispersion, and Diffusion
Figure 2-7 illustrates Darcy's law, the basic equation
used to describe the flow of fluids .through porous
materials. In Darcy's law, coefficient k, hydraulic
conductivity,  is often  called  the coefficient of
permeability by civil engineers.

Darcy's law applied to a soil liner shows the rate of
flow of liquid q directly proportional to the hydraulic
conductivity of the soil and the hydraulic gradient, a
measure of the driving power of the fluid forcing
itself through the soil and the cross-sectional area
"A" of the liner (see Figure 2-7).

If hydraulic conductivity is 10-7 cm/sec, the amount
of leakage for a year, per acre, is 50,000 gallons. If
the conductivity  is 10 times  that value (1 x. 10-6
cm/sec), the leakage is 10 times greater, or 500,000
gallons. Table 2-2 summarizes quantities of leakage
per annum for a 1-acre liner with an amount of liquid
ponded on top of it, assuming a hydraulic gradient of
1.5. Cutting the hydraulic conductivity to 10-8 cm/sec
reduces the quantity of leakage 10-fold  to 5,000
gallons per  acre per year. These data demonstrate
how essential low  hydraulic conductivity is to
minimizing  the quantity of liquid passing through
the soil liner.

Contam/nants
The transport of contaminants through the  soil liner
occurs by either of two mechanisms: advective
                                                 13

-------
   o
                                                                  Leachate
                                                                                              Leachate
          10-9 -
         10-10
             04      8     12     16    20     24

                           Percent Bentonite


 Figure 2-4.  Influence of sodium bentonite on hydraulic
            conductivity.
         Clav Liner
                               Composite Liner
                                                FML
      A = Area of Entire       Area <  Area of Entire
           Liner                    Liner

 Figure 2-5.  Leachate infiltration in clay and composite liner
            systems.
transport,  in which dissolved contaminants  are
carried by flowing water, and molecular diffusion of
the waste through the soil liner. Darcy's law can be
used to estimate rates of flow via advective transport
by calculating the seepage velocity of the flowing
water. Seepage velocity is the hydraulic conductivity
times the hydraulic gradient, divided by the effective
porosity of the soil. The effective porosity  is defined
as the  volume of the pore space that is effectively
                                                                     Do  ,                       Don't

                                                          Figure 2-6. Proper placement of FMLs on clay liners.
     Influent
     Liquid
ent   J
id -/
                                                                                     Soil
                                              Effluent
                                              Liquid
                                                                 q  = rate of flow
                                                                 k  = hydraulic
                                                                      conductivity
                                Hi =  headless
                                L  =  length of flow
                                A; =  total area
                                                                                       V	L
                                                                            Leachate
                                                                             Subsoil
          q  =  kiA

          i   =  Hydraulic Gradient

             _ H + D             |
                 D               |

          (Assumes  No Suction Below Soil Liner)

Figure 2-7. Application of Darcy's Law.
                                                     14

-------
Table 2-2.   Effects of Leakage Quantity on Hydraulic
           Conductivity for a 1-Acre Liner

 Hydraulic Conductivity (cm/sec)    Annual Leakage (gallons)
1 X 10-6 .
1 x 10-7
1 X ID'8
500,000
50,000
5,000
Note: Hydraulic Gradient Assumed to be 1.5

conducting the flow, divided by the total volume of
the soil sample (Figure 2-8).
                                               divided by the hydraulic conductivity times the
                                               hydraulic gradient (Figure 2-9).
                                                                 Leachate
                                                                  Subsoil
                                                                                          .    Ln
                                                                                    TOT = — = -=-2
                                                                                         V     ki
  Flux
I
             Leachate
             Subsoil
                        H
i   = Hydraulic
     Gradient

  _ H +T
     T

  (No Suction)
     i
             Leachate
             Subsoil
                          seepage velocity
                     ne  = effective porosity
Figure 2-8.  Advective transport.
If the liquid uniformly passes through all the pores
in the soil, then the effective and total porosities are
equal.  However, if the flow takes place in only a
small percentage of the total pore space, for example,
through fractures or macropores, the effective
porosity will be much lower than the total porosity.
Judging the effective porosity is one of the problems
of estimating seepage velocities.

If effective porosity and other parameters are known,
the time of travel (TOT)  for a  molecule of waste
transported by flowing water through the soil liner
can be  calculated. TOT equals the length of the
particular flow path times the  effective porosity,
                                                    Figure 2-9.  Time of Travel (TOT).
It is  possible to confirm these  calculations  and
measure some of the parameters needed to make
them by performing  laboratory permeability
experiments.  In these  experiments, clean soil  is
placed into columns in the laboratory, and the
leachate or some other waste liquid is loaded on top
of each soil column, forcing the liquid through the
column over a period of time, while  keeping the
concentration of influent liquid constant. The
concentration of one or more chemicals  in the
effluent liquid is measured over time.

A plot called a breakthrough  curve shows the
effluent liquid concentration c divided by  the
influent liquid concentration c0 as a function of pore
volumes of flow (see Figure 2-10). One pore volume of
flow is equal to the volume of the void space in the
soil. The effective porosity of the  soil is determined
by measuring a breakthrough curve.

It can be expected that  as the leachate invades the
soil, none of the waste chemical will appear in the
effluent liquid at first, only remnant soil and water.
Then at some point, the invading leachate will make
its way downstream through the soil column,  and
come out in more  or less full strength.  An
instantaneous breakthrough  of  the waste liquid
never occurs, however. The breakthrough is  always
gradual because the invading leachate mixes  with
the remnant soil water through a process called
mechanical dispersion.

Many of the waste constituents in the  leachate are
attenuated or retarded by the soil. For example, lead
migrates very slowly through soil, while chloride and
bromide ions migrate very  quickly. With  no
retardation or attenuation, breakthroughs would
occur at c/c0 of 0.5 to 1 pore volume of flow and below
(see Figure 2-11). With effective and total porosities
equal, a  much delayed breakthrough of chemicals
                                                 15

-------
              Leachate
Concentration
of Solute = C0
              Effluent
Concentration
of Solute = c
                                                            No Retardation
                                                                I
                                                                                Retardation
                                                                                              (n = ne)
                          0          1          2

                                    Pore Volumes of Flow

                    Figure 2-11. Effective porosity of soils with retardation and
                              without retardation of waste ions.
                                (for n = ne)
                                       Dispersion
         0                1

                  Pore Volumes of Flow

Figure 2-10.  Effective porosities.
                   the  soil. At the start of the  experiment,  the
                   concentration c is equal to c0 in the waste liquid. The
                   soil is clean. Even though no water flows into the soil
                   by advection, chemicals move into the soil by the
                   process  of molecular diffusion. Eventually,  the
                   concentration of the waste liquid  and the soil will be
                   one and the same (see Figure 2-12).
                                                             Leachate
                                                           (constant c0)
                                                                                   t = 0
                                                   Concentration (c)
                    Figure 2-12. Molecular diffusion.
that have been absorbed or attenuated by the soil
could be expected.

The best way to determine effective porosity is to
perform a test using a "tracer" ion that will not be
absorbed significantly by the soil, such as chloride or
bromide. If the breakthrough occurs in one pore
volume of flow, the effective and total  porosity is
equal.  If, instead, the breakthrough  occurs at half a
pore volume of flow, then the effective porosity is half
the total porosity.

Molecular Diffusion
Chemicals can pass through soil liners by molecular
diffusion, as well as by advective transport. One can
study the molecular diffusion of chemicals in the soil
by compacting soil in the bottom of an impermeable
beaker and ponding waste liquid or leachate on top of
                    Calculations  show  that after  10 to 30  years,
                    molecular diffusion  begins to transport the first
                    molecules of waste  3  feet downwards through a
                    compacted soil liner.  Accordingly,  even  with a
                    perfectly impermeable liner with  0 hydraulic
                    conductivity, in 1 to 3 decades contaminants  will
                    begin to pass through the soil liner, due to molecular
                    diffusion.                        ;

                    The rate of diffusion is  sensitive; to a number of
                    parameters.  For conservative ions  that are not
                    attenuated, the transfer time is 1 to 3 decades. For
                    ions that are attenuated, transfer time is much
                    longer. The mass  rate of transport  by molecular
                    diffusion, however,  is so slow that  even  though
                    chemicals begin to show up in 1  to 3 decades,  the
                    total amount released per unit of area is small.

                    Flexible membrane liners  permit the release of
                    organics and vapors via molecular diffusion by
                                                 16

-------
almost exactly the same process. Transport times for
organic chemicals through FMLs typically range
from a few hours to a few days.

Laboratory Tests for Hydraulic
Conductivity
The hydraulic conductivity of a soil liner is the key
design  parameter. The important variables  in
hydraulic conductivity testing in the laboratory are:

• Representativeness of the sample.

• Degree of water saturation.

• Stress conditions.

• Confinement conditions.

• Testing details.

flepresentaf/Veness of Sample: Case
Histories
Representativeness of the soil  sample being tested is
the most crucial factor. Two case histories illustrate
the importance and  the  difficulty of obtaining
representative samples.

Klingerstown, PA
A test pad constructed under EPA sponsorship  in
Klingerstown, Pennsylvania,  consisted of a pad  of
clay soil 30 feet wide, 75 feet  long, and 1 foot thick.
The clay liner was built in three lifts, or layers, each
lift being 4 inches thick. The liner was built up on a
concrete pad  so that researchers could crawl under
and collect and measure the liquid coming out of the
bottom. A shelter was  built over  the test pad and
about 1 foot of water ponded over the surface.

The principal investigator,  Dr. Andrew Rogowski,
divided the  collection units into a  number  of
subunits, each subunit measuring 3 feet by 3 feet. A
total of 250 different collection units underneath the
soil  liner were monitored independently  to
determine rate of flow. Dr. Rogowski's objective was
to  correlate the  variability of the hydraulic
conductivity of the liner with the molding water
content of the soil and with the dry density of the
compacted soil.

Dr. Rogowski also installed 60 1-foot diameter rings
in the surface of the liner, so that he could measure
independently 60 different infiltration rates on the
surface  of the liner. Each of the 3-square-foot (ft2)
blocks  was  assigned an  average hydraulic
conductivity based on many months of testing and
observation. Figure 2-13 shows the results. The zone
at  the top of the diagram  with a high hydraulic
conductivity of 10-5 cm/sec  probably resulted from
 the way the liner was built. The sheepsfoot roller
 used to compact the liner probably bounced on the
 ramp causing lower compaction, which resulted in a
 relatively  high conductivity  at  the end. The
 conductivity for the rest of the liner varies between
 10-6 and lO-8 cm/sec, a 100-fold variation of hydraulic
 conductivity.
     10-5 cm/s


     10-6 cm/s


     10'7 cm/s


     10'8 cm/s
                                            75ft
                            30ft
 Figure 2-13. Hydraulic conductivity zones from Klingerstown,
           PA Tests.
 For a laboratory test on this soil, the test specimen
 would need to measure about 3 inches in diameter
 and 3 inches  in height. Finding a 3-inch diameter
1 sample representative of this large mass of soil
 presents  a challenge, since small  samples  from
 larger quantities of material inevitably vary in
 hydraulic conductivity.

 Dr. Rogowski's  experiments resulted in  two
 interesting sidelights. First, the average  of all the
 hydraulic conductivities was 2 to 3 x 10-7 cm/sec. Dye
 was poured into the water inside some of the 1-foot
 diameter rings installed in the surface of the liner to
 determine if the dye came out directly beneath the
 ring or off to  the side. In some cases it  came out
 directly beneath the ring and in some it wandered off
 to the side. It took only a few hours, however, for the
 dye to pass through the  soil liner, even with an
 average conductivity only slightly greater than 1 x
 ID-7 cm/sec. A few preferential flow paths connected
                                                17

-------
to some of the rings allowed very rapid transit of the
dye through the soil liner.

The second interesting sidelight was Dr. Rogowski's
conclusion that no,relationship existed between in
situ hydraulic conductivity and either molding water
content of the soil or the dry density of the compacted
soil.

The soil used in the experiment was a low plasticity
sandy material with a PI of about 11 percent. The
variations in  hydraulic conductivity probably
reflected zones of material that contained more sand
in some places  and more clay in others. Tests have
been performed on a couple of liners in  the field
where  liquid flowing into the  soil liners has been
dyed and traced by cutting  a cross section or trench
through the liner.  Typically, a pattern such as that
shown in Figure 2-14 emerges, with the horizontal
dots indicating lift interfaces.  The results  seem to
indicate that dyed liquid finds a defect in the top lift,
moves down and spreads along a more permeable
zone between  lifts;  finds  another defect, moves
downward, spreads; finds another defect and so forth.

            	2.	
                           Dyed water
  3R
                6 In.
                      I          I         I
 Figure 2-14. Liquid flow between lift interfaces in a soil liner.
 The problem arises in determining from where a
 representative sample should be taken. Even if 25
 samples were picked randomly in a grid pattern from
 that zone for 25 independent measures of hydraulic
 conductivity, it would be unclear how to arrive at a
 single representative measure. The flow through a 3-
 inch diameter specimen is much too small to mimic
 the patterns of fluid flow that occur in the field under
 similar conditions.

 Houston, TX
 A  second case  history  that  demonstrates the
 difficulty of obtaining  representative  samples
 involves a trial pad constructed in Houston in 1986.
A 1-foot thick clay liner was compacted over a gravel
underdrain with an area roughly 50 feet by 50 feet.
The entire area of the liner was drained and the flow
from an area roughly 16 feet by 16 feet was carefully
collected and measured.

The liner was first built on top of the underdrain, the
soil compacted with a padfoot roller, and water
ponded on top of the liner. Infiltro'meters measured
the rate of inflow, and a lysimeter measured the rate
of outflow. The soil used in the experiment was
highly plastic with a PI of 41 percent.

The liner was compacted with two lifts, each 6 inches
thick. A 1-ft3  block of soil was carved from the liner,
and cylindrical test specimens we|re trimmed from
upper and lower lifts and measured for hydraulic
conductivity.  A 3-inch diameter specimen also was
cut, and hydraulic  conductivity parallel to the lift
interface was measured.          i

Table 2-3 summarizes the results! of these various
tests. The actual in situ hydraulic conductivity, a
high  1  x  10-4 cm/sec, was verified both by the
infiltration  measurements and^ the underdrain
measurements.

Table 2-3. Hydraulic Conductivities from, Houston Liner Tests

Actual k: 1 x 10/4 cm/s                '.
Lab K's:
                                                         Location
                                                                         Sampler
                                      K (cm/s)
Lower Lift
Upper Lift
Lift Interface
Lower Lift
Upper Lift
3-in Tube
3-in Tube
3-in Tube
Block :
Block
4x10-9
1 X 10-9
1 x 10-7
8 x 10-5
1 x 1 0-8
 The tests were replicated under controlled conditions
 using soil collected from the liner in thin-walled 3-
 inch diameter sample  tubes. The laboratory
 measures of hydraulic conductivity were consistently
 1 x 10-9 cm/sec, five orders of magnitude lower than
 the field value of 1 x 10-4 cm/sec. The laboratory tests
 yielded  a  hydraulic  conductivity 100,000  times
 different than that from the field test. Apparently
 the flow through the 3-inch specimens did not mimic
 flow on a larger scale through the entire soil liner.
 The sample trimmed horizontally at the lift interface
 was actually obtained by taking a 3-inch diameter
 sample  from a sample  collected, with a 5-inch
 diameter tube. The hydraulic conductivity with flow
 parallel to the lift interface was two orders of
 magnitude higher.               :

 Of all the values recorded from the lab tests, only the
 one obtained from the upper lift of the block sample
 was close  to the  field value of ,1 x 10-4 cm/sec.
                                                 18

-------
Apparently that one block sample happened to hit
one of the more permeable zones and, more or,less by
accident, yielded a  lab measurement that agreed
with the field measurement.

Degree of Water Saturation
The hydraulic conductivity obtained in a laboratory
test also can be affected by the amount of gas present
in the  soil. Dry  soils are less permeable than wet
soils. A dry soil primarily is filled with air. Because
invading water does not flow through air-filled voids,
but only through water-filled voids, the dryness of a
soil tends to lower permeability.

Some engineers  believe that hydraulic conductivity
tests on compacted clay soil should be performed on
fully saturated soils in an attempt to measure  the
highest possible  hydraulic conductivity. Most if not
all  of the gas can be eliminated from  laboratory
hydraulic conductivity tests by backpressure
saturation of the soil. This technique pressurizes the
water  inside the soil, compressing the.gas and
dissolving it  in  the water.  Increasing the
backpressure  will  increase  the  degree of water
saturation and reduce the amount of air, thereby
increasing hydraulic conductivity.

Stress Conditions
Another factor substantially  influencing the
hydraulic conductivity of compacted clay soil is the
overburden, or confining pressure, acting on the soil.
The weight of 1 foot of soil overburden is roughly
equivalent to 1 pound per square inch  (psi). If two
identical samples of soil are  buried, one near  the
ground surface and one at depth, the soil near the
ground surface is likely to be more permeable than
the soil buried at depth, simply because the soil
buried at depth  is squeezed  into a more compact
configuration by the overburden pressure. Thus, soil
has a lower porosity with increasing depth.

In a series of experiments performed a few years ago,
slabs of clay were compacted in the lab and then
trimmed to produce cylindrical test specimens. One
sample of the clay was compacted and then trimmed
for a test specimen immediately, while the other was
allowed to desiccate for a period of time before being
trimmed. The one that desiccated had tiny cracks as
a result of the desiccation process,  and was much
more permeable than  the soil that had not been
desiccated. As  confining stress increased, the
hydraulic conductivity decreased because the soil
was compacted into a less porous condition.

Although the sample that was  cracked  from
desiccation was obviously more permeable, at a very
high stress the hydraulic  conductivities  were
essentially identical (see Figure 2-15). With enough
confining pressure acting on the soil, the cracks that
had existed earlier closed up completely so that the
soil was no longer highly permeable.
                        (kPa)
                         50
                                       100
        10-7
        TO'8
    E
    o
    O
    o
    1
    I-
        10-9
                         . Sample Containing
                          Desiccation
                          Cracks
Sample Containing
No Desiccation
Cracks
            0      4       8       12
                Effective Confining Pressure (psi)
                            16
 Figure 2-15. Hydraulic conductivity as a function of confining
           pressure.
One implication of these experiments for laboratory
hydraulic conductivity testing is that conductivity
values can vary remarkably depending on the
confining stress. It is essential that the  confining
stress  used in a laboratory test be  of the  same
magnitude as the stress in the field.

Another  important implication is  that highly
permeable soil liners generally have  defects, such as
cracks, macropores, voids, and zones that have not
been compacted properly. One opportunity  to
eliminate those defects is at the time of construction.
Another  opportunity arises after the landfill is  in
operation and the weight of overlying solid waste or
of a cover over the whole system further compresses
the soil. This compression, however, occurs only  on
the bottom liners, as there  is not much overburden
stress on a final  cover placed over a solid waste
disposal unit. This is one reason it is more difficult to
design and implement  a  final cover with low
hydraulic conductivity than it is a bottom liner. Not
only is there lower stress acting on a cover than on a
liner, but the cover is  also subjected to many
environmental forces which the liner is not.
                                                19

-------
Double-ring and Flexible Wall Permeameters

A  double-ring  permeameter separates flow that
occurs through the central part of the soil sample
from  flow that occurs near the side wall. The
permeameter is designed such that a ring sticks into
the bottom of the soil sample, thereby detecting
sidewall leakage that might invalidate the results of
laboratory conductivity tests. Almost all of the rigid
wall permeameters now being  installed  in the
University of Texas laboratories have double rings.
Another kind of permeameter cell is a flexible-wall
permeameter in which the soil specimen is confined
by a thin, flexible membrane, usually made of latex.
The latex membrane conforms to  any irregularities
in the sample, an  advantage  when  collecting
irregularly shaped specimens from the field.

Termination Criteria

When conducting laboratory hydraulic conductivity
tests, two criteria should be met  before testing is
terminated. First, the rate of inflow should be within
10 percent of the rate of outflow. Measuring both the
rate of inflow and the rate of outflow is necessary to
detect problems such as a  leak  in the system or
evaporation from one of the reservoirs. Second, a plot
of hydraulic conductivity versus time or pore volume
of flow should essentially level off, indicating that
hydraulic conductivity is steady.

ASTM has no  standards at the  present  time for
testing low-hydraulic- conductivity soil, but is in the
final stages of developing a  standard for tests with
flexible wall permeameters that should be available
within the next 2 years.

Field Hydraulic Conductivity Testing
In situ, or field, hydraulic conductivity testing
operates  on the assumption that  by testing larger
masses of soil in the field one  can obtain more
realistic results. There are actually four kinds of in
situ hydraulic conductivity tests:  borehole tests,
porous probes,  infiltrometer tests, and underdrain
tests. To  conduct a borehole test one simply drills a
hole in the soil, fills the hole  with water, and
measures the rate at which water percolates into the
borehole.

The second type of test involves driving or pushing a
porous probe into the soil and pouring water through
the probe into the soil. With this  method,  however,
the advantage of testing directly  in the field is
somewhat offset by the limitations of testing such a
small volume of soil.

A third method of testing involves a device called an
infiltrometer. This device  is embedded  into the
surface of the soil liner such that the rate of flow of a
liquid into the liner can be measured. Infiltrometers
have the advantage of being able to permeate large
volumes of soil, which the first two devices cannot.

A fourth type of test utilizes an underdrain, such as
the one at the Houston test site discussed earlier.
Underdrains are  the most accurate  in situ
permeability testing device because they  measure
exactly what comes out from the bottom of the liner.
They are, however, slow to generate good data for
low permeability liners because they take a while to
accumulate  measurable flow. Also, underdrains
must be  put in during construction, so there  are
fewer in operation  than there are other  kinds of
testing devices. They are highly recommended for
new sites, however.

The two  forms of infiltrometers popularly  used  are
open and sealed. Four variations are illustrated in
Figure 2-16. Open rings are less desirable because
with a conductivity of  1O7 cm/sec,  it is difficult to
separate a 0.002 inches per day drop in water level of
the pond from evaporation and other losses.
       \
     Open, Single Ring
                            \
 Open, Double Ring
    Sealed, Single Ring
                            \
Sealed, Double Ring
 Figure 2-16. Open and sealed single- and double-ring
           infiltrometers.
With sealed rings, however, very low rates of flow
can be measured. Single-ring infiltrometers  allow
lateral flow beneath the ring,  complicating the
interpretation of test results. Single rings are also
susceptible to the effects of temperature variation; as
the water heats up, the whole system expands and as
it  cools down, the  whole system contracts. This
situation could lead to erroneous^ measurements
when the rate of flow is small.

The sealed double-ring infiltrometer has proven the
most successful and is  the one used currently. The
outer ring forces the infiltration from the inner ring
to be more or less one dimensional. Covering the
                                                20

-------
inner ring with water insulates it substantially from
temperature variation.

Figure 2-17 shows the double ring device currently
being used. It consists of a 12-foot by 12-foot outer
ring and a 5-foot diameter inner ring. Tensiometers
are embedded  at various depths  to establish the
depth of water penetration  into the soil so that
hydraulic conductivity can be calculated.
       Sealed Inner Ring
 Flexible Bag N
Tensionmeters
  Outer Ring
 Figure 2-17.  Details of a sealed double-ring infiltrometer.
Rate of infiltration is measured by a small flexible
bag. As water infiltrates from the inner ring into the
soil, the  flexible bag is gradually compressed as
water leaves it to enter the ring. To determine how
much flow has  taken place, the flexible  bag is
disconnected, dried off, and weighed.  Then it can
either be refilled or replaced with a fresh bag.

The flexible bag also serves to stabilize pressure
between the inner and outer rings. If the water level
in the outer ring changes, the hydrostatic pressure
on the flexible bag changes by precisely the same
amount.  Thus, even though the water level in the
outer ring fluctuates, the  differential pressure
between  the inner and outer rings is always  zero.
Overall,  this simple device compensates for water
level changes and allows a range of measurements,

Installation  of the Sealed Double-ring
Infiltrometer
The sealed double ring infiltrometer is best used on a
test pad. The width of the test pad is usually about 40
feet by 50 feet; the thickness of the test pad usually 2
or 3 feet. The  test  pad  is always covered to prevent
desiccation after construction has been completed.

The 12-foot by 12-foot outer ring is made of four
aluminum panels that  are assembled at the site. A
prefabricated design allows the panels to be bolted
together  to prevent breaching. The outer box can
then be lifted  up and put into position embedded in
the liner. If the site is sloping, the elevation of the
four corners is measured at the site with a handheld
level or a transit, so that the top of the infiltrometer
is more or less horizontal and the water level is even
with the top of the infiltrometer.

A rented ditching machine is used to excavate a
trench about 18 inches deep and 4 inches wide for the
outer ring. The ring is embedded into the trench and
the elevations are checked again.

The sealed inner ring typically is made of fiberglass
and measures 5 feet by 5 feet. It slopes from left to
right and from side to side in a dome-shaped slope
such that it has a high point. As the ring fills with
water from the bottom up, gas is  displaced out  the
top. When the inner ring is completely full of water,
the gas is purged out of the system.

The trench for the  inner ring is not  dug with  the
ditching device because the vibration and churning
action might open up fractures in the soil and change
the measurements.  Instead, the trench is dug in one
of two ways: by a handheld mason's hammer or by a
chain saw. A chain saw with a specially  equipped
blade is the state-of-the-art in excavation of trenches
for the inner ring.

While the excavation is being done, the working area
is covered with plastic. Before the system is ready to
be filled with water, a pick or rake is used to scrape
the surface thoroughly to ensure that smeared soil
has not sealed off a high hydraulic conductivity zone.

After the trench has been excavated, it is filled with
a grout containing  bentonite that  has been mixed
with water to the consistency of paste. A grout mixer
rather  than a concrete mixer is used to provide more
complete mixing. The inner ring is then forced into
the grouted trench. The grout is packed up against
the ring to obtain the best possible seal. To pretest
the seal, the inner ring is filled with about 3 inches of
water. If there is a gross defect at the seal, water will
spurt out of it. Next,  the outer ring is placed in its
grout-filled trench.

The next step is to tie steel cords in the middle of the
four sections to prevent the outer ring from bowing
out from the pressure of the water. Tensiometers are
installed in nests of three at three different depths to
monitor the depth of the wetting process. To cushion
the tensiometers, soil is excavated and mixed with
water  to  form  a paste.  The tensiometer is then
inserted into the hole which is then sealed with
bentonite. The depths of the porous tips are typically
6 inches,  12 inches, and 18 inches in each nest of
three. Finally, the system is ready to fill with water.

The small flexible bag used can be an intravenous
bag from the medical profession, available in a range
                                                21

-------
of sizes from a few hundred milliliters to larger sizes.
A ruler taped to the inside of the outer ring can be
used to monitor the water level, which should be kept
to within +/-1 inch of its original level.

When the construction process is complete, the entire
unit is covered with a tarp. The tarp minimizes water
evaporation and  keeps  the temperature from
fluctuating.

After  the infiltrometer has  been installed,
measurements are taken over a period lasting at
least 2 weeks and  often as much as 1 to 2 months.
Readings involve removing the bag, weighing the
bag, and refilling it with water.  Readings  might be
taken as infrequently as once a week or as frequently
as once a day, depending on the situation.

An  experienced group of people can put in a sealed
double ring infiltrometer in 1 day. Two days is more
typical for less experienced people.

The cost of the equipment  to build a sealed double
ring infiltrometer is about $3,000. The tensiometers,
grout, and equipment rental typically add another
$1,500. The total cost for equipment and installation,
plus the periodic monitoring of the  flow  rate and
analysis of test data is approximately $10,000, not
including the cost  of a trial pad. The sealed double
ring infiltrometer  itself is  reusable, therefore the
$3,000 cost of the rings is recoverable. In comparison
to the  cost of infiltrometer  installation and
operation, a single  laboratory hydraulic conductivity
test costs only $200 to $400.


Issues Associated with Field Hydraulic
Conductivity  Testing
A number of issues are associated with all  field
hydraulic conductivity tests. Most importantly, the
tests do  not directly measure the  hydraulic
conductivity (k) of the soil. Instead they measure the
infiltration rate (I) for the soil. Since hydraulic
conductivity  is the infiltration rate divided by the
hydraulic gradient (i) (see equations in Figure 2-18),
it is necessary to determine the hydraulic  gradient
before k can be  calculated. The following equation
(with terms defined in Figure 2-18) can be used to
estimate the hydraulic gradient:

 i = (D+Lf)/Lf

This equation assumes the pressure head at the
wetting front equal to zero. The value of the pressure
head is, however, a source of disagreement and one of
the sources of uncertainty  in this test. The
assumption  that the pressure  head is zero is a
conservative assumption, tending to give a high
hydraulic conductivity.
         I  = Infiltration Rate
           = (Quantity of Flow/Area)/Time
           = (Q/A)/t

         k  = Hydraulic Conductivity
           = Q/(iAt) = l/i

Figure 2-18.  Hydraulic gradient.
A  second issue  is  that of effective stress  or
overburden stress. The overburden stress on the soil
is essentially zero at the time the test is performed,
while  under  operating  conditions, it  may  be
substantial.  The influence of overburden stress  on
hydraulic conductivity cannot be estimated, easily in
the field, but can be measured in the laboratory.
Using conservative estimates, the shape of the field
curve should be the  same as that; obtained in the
laboratory (see Figure 2-19). If thiere is significant
overburden stress under actual field performance,
the infiltrometer test measurements would need to
be adjusted according to the laboratory results.

A third issue that must be considered is the effect of
soil swelling on hydraulic conductivity (see Figure 2-
20). Tests on highly expansive  soils almost  always
take longer  than  tests with other  soils, typically
lasting 2 to  4 months. This is a particular problem
with soils along the Texas Gulf Coast.

A hydraulic conductivity test is terminated when the
hydraulic conductivity drops below 10-7  cm/sec (see
Figure 2-21). It usually takes 2  to;8 weeks to reach
that point, and is usually clear after about 2 months
whether or not that objective will be achieved.

The ASTM standard for double-ring infiltrometers is
currently being revised. The existing double-ring
test (D3385) was  never intended  for low hydraulic
conductivity soil  and should not ibe used on clay
liners. A new standard for double-ring infiltrometers
                                                 22

-------
                                                                      Termination of Test
  t
  1
  •o
  S
  g
  o
   o
  O
   to
  •§,
                                                        10-7
                     Effective Stress
                                                                                               Time
Figure 2-19.  Hydraulic conductivity as a function of effective
           stress.
 Figure 2-21. Termination of testing.
Figure 2-20.  Soil swelling.
intended for low hydraulic conductivity soils will
probably be available in 1990.

Field Tests versus Laboratory Tests
A  comprehensive program of testing soil liner
materials will involve both laboratory and field tests.
Field tests provide an opportunity to permeate a
larger, more representative volume of soil than do
laboratory tests. A field test  is  also  more
comprehensive and more reliable.

A primary advantage of laboratory tests is that they
are less expensive so more of them can be performed.
Also, certain conditions can be simulated in a lab
that cannot be duplicated in the field.  One can
saturate the soil fully in the laboratory, getting rid of
all the gas. One can also vary the overburden stress
in the lab, which cannot be done conveniently in the
field. Finally, in the lab,  actual waste liquids can be
passed through a column of material for testing, a
condition that could not be duplicated in the field.

There is a radical variation in the reliability of field
tests versus laboratory tests. In the Houston test pad
discussed  earlier  the real value  for hydraulic
conductivity in the field was 1 x 10-4 cm/sec while the
lab  values  were  1 x  10-9 cm/sec, a 100,000-fold
difference in the values.

At the Keele Valley landfill, just outside Toronto,
however, some excellent field data  have been
obtained. At this particular site, a 3-foot clay liner
spanning 10 acres is monitored by a series  of
underdrains. Each underdrain measures 15  m2 and
is made  of high density polyethylene.  The
underdrains track the  liquid as it moves down
through the  soil liner. The underdrains have been
monitored for more than  2 years  and have
consistently  measured hydraulic conductivities  of
. about 1 x 10-8 cm/sec. Those field values essentially
are identical to the laboratory values.

:The clay  liner at  Keele Valley was  built very
carefully  with strict  adherence to construction
quality assurance. The laboratory and field values
are the same because the liner is essentially free of
defects. Lab and  field values differ when the soil
liner in the  field contains defects that cannot be
simulated accurately on small specimens. If the soil
                                                23

-------
is homogeneous, lab and field tests should compare
very well.

Attack by Waste Leachate
Acids and Bases
Acids can attack soil by dissolving the soil minerals
into other constituents. Typically, when acids are
passed through soil, hydraulic conductivity drops
because the acids dissolve the materials that help to
neutralize them. After large amounts of acid wash
into the soil, hydraulic conductivity decreases.

There is real concern over waste impoundments used
to store acidic liquid. Small amounts of acid such as
that contained in a barrel in a solid waste landfill
underlain by a 3-foot thick liner will not inflict major
damage on the soil liner. A large volume of liquid in
the impoundment,  however, can damage the  soil
seriously.

Neutral Inorganic Compounds
Nonacidic liquids can change hydraulic conductivity
in other ways. Soil  is made up of colloidal particles
that have negative charges along the surface. Water
is a polar molecule, with atoms arranged or aligned
asymetrically.  This alignment allows  the water
molecule to be  attracted electrochemically to the
surfaces of the negatively charged soil particles (see
Figure 2-22).
of water and ions surrounding the clay particles,
known as the diffuse double layer.

The water and ions in the double layer are attracted
so strongly electrochemically to the clay particles
that they do not conduct fluids. Fluids going through
the soil go around the soil particles and, also, around
the double layer. The hydraulic conductivity of the
soil,' then,  is controlled very 'strongly by  the
thickness of these double layers. When  the double
layers shrink, they open  up flow paths resulting in
high hydraulic conductivity. When  the layers swell,
they constrict flow paths, resulting in low hydraulic
conductivity.                  '

The  Gouy-Chapman Theory relates electrolyte
concentration, cation valence, and dielectric constant,
to the thickness of this double layer (see Figure 2-
23). This theory was originally developed for dilute
suspensions  of solids  in  a  liquid.  However,
experience confirms  that the principles can be
applied qualitatively to soil, even compacted soil that
is not in suspension.
       Oouv-Chapman Theory:  .
                                                                           Thickness «
                                                                                        D
                                                           D = Dielectric Constant

                                                           n0 = Electroylte Concentration

                                                           V = Cation Valence

                                                    Figure 2-23. Gouy-Chapman Theory.
      +     +     •»•     +•+     +     +     +


   y'V  ^-^  V^  f^  *"^  ¥^*  V^*   «**^
 Figure 2-22. Water and clay particle molecules.
It is also possible for ions in the water, especially
positively charged ions, or cations, to be attracted to
the negatively charged surfaces. This leads to a zone
The following application of the Gouy-Chapman
Theory uses sodium bentonite. The ion in the soil is
sodium, which has a charge of +1. The electrolyte
valence in the Gouy-Chapman Theory is v = 1. The
permeating liquid is rich in calcium, and calcium has
a charge of +2. As calcium replaces sodium, the
valence (v) in the Gouy-Chapman equation goes from
1 to 2. A rise in v increases the (denominator, thus
decreasing the thickness (T). As Tj decreases and the
double layer shrinks, flow paths open up making the
soil more permeable, as shown in Figure 2-24.

Since calcium bentonite, typically, is 100 to 1,000
times more permeable than sodium  bentonite, the
                                                  24'

-------
                    Flow
               Clay
               Particle
 Figure 2-24. The diffuse double layer.
Double
Layer
introduction of this permeating liquid could change
hydraulic conductivity substantially.

Table 2-4 shows  that soils  containing  polyvalent
cations  having high valence and high  electrolyte
concentration  have a high conductivity, while the
soils containing monovalent cations, like sodium,
have a low k.  Distilled water at the extreme end of
the spectrum  is Tree of electrolytes. In the Gouy-
Chapman  equation,  then, no  the electrolyte
concentration, would be  0.  The  denominator,
therefore, would go to 0 and the T value to infinity.

Table 2-4. Electroylte Concentration
     High k    Water with Polyvalent Cations

               Tap Water (Note Variation)

               Water with Monovalent Cations

     Low k      Distilled Water
Consequently, if the free ions in the soil water are
leached out, the double  layers swell tremendously,
pinching off flow paths  and resulting in very low
hydraulic conductivity. Data have shown hydraulic
conductivity to be as much as two to three orders of
magnitude lower when measured  with distilled
water  than with other  kinds of water. For this
reason, distilled water should not be used in testing
the hydraulic conductivity of a clay liner.

An ASTM standard under development recommends
using 0.005 normal calcium sulfate as1 the standard
 permeating  water, because of its medium range
 electrolyte concentration. Calcium sulfate,  with
 divalent calcium, will usually not reduce hydraulic
 conductivity.

 Neutral Organic Compounds
 Organic chemicals can cause major changes in
 hydraulic conductivity. The dielectric constant (D) of
 many of the organic solvents used in industry is very
 low. For example, the dielectric constant of water is
 about  80, while the dielectric constant of
 trichloroethylene is about 3. Using the Gouy-
 Chapman equation, if D decreases, which means the
 numerator decreases,  the  value for  T will  also
 decrease, causing the double layer to  shrink. The
 effect of replacing water with an organic solvent then
 is to shrink the double layer and open up flow paths.

 In addition to opening up flow paths, as the double
 layers  shrink,  the  solvent flocculates  the  soil
 particles,  pulling them together and  leading to
 cracking in the soil. Permeation of the soil with an
 organic chemical,  such as gasoline, may  produce
 cracking similar to that associated with desiccation.
 The organic solvent, however, produces a  chemical
 desiccation rather  than a desiccation of the soil by
 drying out.

 Laboratory test data indicate  that if the  organic
 chemical is present in a dilute aqueous solution, the
 dielectric constant will  not be dangerously low. A
 dielectric constant above 30 generally will not lower
 the conductivity substantially enough to damage the
 soil. Two criteria need to be met for a liquid not to
 attack'clay liners:  (1) the solution must contain at
 least 50 percent water, and (2) no separate phase or
 organic chemicals can be present.

 Termination Criteria
 Chemical  compatibility  studies  with hydraulic
 conductivity tests must  be performed over a long
 enough period of time to determine  the full effects of
 the waste liquid. Termination criteria include equal
 inflow and outflow  of liquid, steady hydraulic
 conductivity,  and influent/effluent  equilibrium. At
 least two  pore volumes of liquid  must be passed
 through the soil to flush out the soil water and bring
 the waste leachate  into the soil in  significant
 quantities  (see  Figure  2-25).  Reasonable
 equilibrations of the  influent and  effluent liquids
occur when the pH of the waste influent and  effluent
 liquids are similar and the key organic and inorganic
 ions are at full concentrations in the effluent liquid.

Resistance  to Leachate Attack
 It is possible to make soils more resistant to chemical
attack. Many of the same methods used to lower
hydraulic  conductivity can stabilize  materials
against  leachate attack,  including greater
                                               25

-------
    Water
Organic Chemical
               0             1

                Pore Volumes of Flow
 Figure 2-25.  Hydraulic conductivity as a function of pore
           volumes of flow.
compaction, an increase in overburden stress, and
the mixing of additives such as lime cement or
sodium silicate with the natural soil materials.

Figure 2-26 shows the results of an experiment
conducted  using a soil called SI, an illitic  clay
containing  chlorite from Michigan. Two sets of data
show the results of permeation of the regular soil, .
first with water and then with pure  reagent grade
heptane. The heptane  caused  the hydraulic
conductivity of the  regular compacted soil to
skyrocket. About 8 percent cement was then added to
the soil.

After treatment of the soil with Portland cement,
however, the heptane did not affect the soil  even
after a pore volume  of flow. The Portland cement
glued the soil particles together so that the soil
became invulnerable to attack, rather than causing
it to undergo chemical desiccation.

References
1.  Daniel, D.E.  1987. Earthen liners  for  land
    disposal facilities.  Proceedings, Geotechnical
    Practice for Waste Disposal 1987,  Univ. of
    Michigan, Ann Arbor, Michigan,  June 1987: 21-
    39. New York, NY: American Society of  Civil
    Engineers.

2.  Trautwein Soil Testing Equipment Company.
    1989. Installation and operating instructions for
    the sealed double-ring infiltrometer.  Houston,
    Texas: Trautwein Soil Testing  Equipment
    Company.
                                                           10-5
                                                          ID'6

                                 O   10-7
                                 o

                                 |

                                 £   10-8
                                                           10-9
                                                          10-10
Clay Stabilization Research;
Soil: S1
Stabilization: Cement
Organic Chomical: Heptane
                                                                            Cement Stabilized
                                                                                         Key
                                                                                       Unstabilized
                                                                                       Stabilied
                                       •2.00    0.00     2.00   4.00     6.00
                                                  Pore Volumes of Flow
                                                                                                8.00
                               Figure 2-26. Illltic-chlorated clay treated with heptane and
                                         with Portland cemant.
                              3.  U.S. EPA. 1986a. U.S. Environmental Protection
                                 Agency. Design, construction,; and evaluation of
                                 clay liners for waste  management facilities.
                                 Technical Resource Document.  Report  No.
                                 EPA/530/SW-86/007, NTIS Order No. PB86-
                                 184496/AS. Cincinnati, Ohio: EPA.
                                                             i
                              4.  U.S. EPA. 1986b. U.S. Environmental Protection
                                 Agency. Saturated hydraulic  conductivity,
                                 saturated leachate  conductivity, and intrinsic
                                 permeability. EPA Method 9ltiO. EPA.
                                                26

-------
                          3.  FLEXIBLE MEMBRANE LINERS
 Introduction
 This chapter discusses several material and design
 considerations for flexible membrane liners (FMLs).
 It highlights some of the problems encountered in
 designing "bathtub"  systems for hazardous waste
 landfills and describes the impact of proposed
 regulations on material and design considerations.

 Composite Liners: Clay versus Synthetic
 Components
 After a landfill site has been chosen and a basin has
 been excavated, the basin is lined with one or more
 layers of water-retaining material (liners) that form
 a  "leachate bathtub." The contained leachate is
 pumped out through a network of pipes and collector
 layers. Liners  may  be constructed of synthetic
 polymer sheets or  of clay. EPA's minimum
 technology guidance (discussed in Chapter One)
 relies on a composite liner that utilizes advantages
 obtained from combining both liner systems.

 Understanding the basic hydraulic mechanisms for
 synthetic liners and clay liners is very important in
 appreciating  the advantages of a composite liner.
 Clay liners are controlled by Darcy's law (Q = kiA)
 (Darcy's law is discussed in more detail in Chapter
 Two).  In clay liners, the factors that most influence
 liner performance are hydraulic head and soil perme-
 ability. Clay liners have  a higher hydraulic
 conductivity and thickness than do synthetic liners.
 Additionally, leachate leaking through a clay liner
 will undergo chemical reactions that reduce the
concentration of contaminants in the leachate.

 Leakage through a synthetic liner is controlled by
Pick's first law, which applies to the process of liquid
diffusion through the  liner membrane. The diffusion
process is similar to  flow governed by Darcy's law
except it is driven by concentration gradients and not
by hydraulic head. Diffusion rates in membranes are
very low in comparison to hydraulic flow rates even
in clays. In synthetic liners, therefore, the factor that
most influences liner performance is penetrations.
 Synthetic liners may have imperfect seams or
 pinholes, which can greatly increase the amount of
 leachate that leaks out of the landfill.


 Clay liners, synthetic liners, or combinations of both
 are required in landfills. Figure  3-1 depicts  the
 synthetic/composite double liner system that appears
 in EPA's minimum technology guidance. The system
 has two synthetic flexible membrane liners (FMLs):
 the primary FML, which  lies between two leachate
 collection and removal systems (LCRS), and  the
 secondary FML,  which overlies a  compacted clay
 liner to form a composite secondary liner. The ad-
 vantage  of the composite liner design is  that by
 putting a fine grain material beneath the membrane,
 the impact of given penetrations can be reduced by
 many orders of magnitude (Figure 3-2). In the figure,
 Qg is the inflow rate with gravel and Qc is the inflow
 rate with clay.


 Figure 3-3 is a profile of a liner that appeared in an
 EPA design manual less than  a year ago. This
 system is already dated. Since this system was
 designed, EPA has changed the minimum hydraulic
 conductivity in the secondary leachate collection
 system from 1 x 10-2 cm/sec to 1 cm/sec to improve
 detection time. To meet  this requirement, either
 gravel or a net made of synthetic material must be
 used to build the secondary leachate collection
system; in the past, sand was used for this purpose.


 Material Considerations
Synthetics are made up  of polymers—natural or
synthetic compounds of high molecular weight.
Different polymeric materials may  be used  in the
construction of FMLs:


• Thermoplastics—polyvinyl chloride (PVC)
• Crystalline thermoplastics—high density poly-
  ethylene (HOPE), linear low density polyethylene
  (LLDPE)
                                              27

-------
                                                                                     Primary FML

                                                                                Secodary FML
                                                ompacted Clay Liner
                                                    Native Soil Foundation
                       (Not to Scale)


Figure 3-1. Synthetic/composite double liner system.
                      Qn « 105 CL
 Figure 3-2. Advantage of composite liner.


•  Thermoplastic elastomers—chlorinated poly-
   ethylene (CPE), chlorylsulfonated  polyethylene
   (CSPE)
•  Elastomers—neoprene, ethylene propylene diene
   monomer (EPDM)

Typical compositions of polymeric  geomembranes
are depicted  in Table 3-1. As the table shows,  the
membranes contain various admixtures such as  oils
and fillers that are added to aid manufacturing of the
FML but may affect future performance. In addition,
many polymer FMLs will cure once installed, and the
strength and elongation characteristics  of certain
FMLs will  change with time.  It is important
                                                         Minimum
                                                        Thickness
                                                        —r~—
                                                        15 cm
30 cm

  j.076 cm

30 cm
                                                           .076 cm
90 cm
         ,•.; ;••-•.-!••.••- «>.-•?. -•.r..<.-.-:,^,:;v
         :o;.-;:r;''-  Solid Waste .'•"••^i
         .*-r.r*::.i •• , r.r.-•'.--^..^'-^i
                 Filter Media

             Hydraulic Conductivity
                     10-2 cm/secr"~y
                                                                   /^\a 1
                                                                      Hydraulic Conductivity
                                                                       > 1 x 10-2
                                                                   s~\ > 1
                                                                                     '/-\
              Hydraulic Conductivity
               < 1 x 10'7 cm/sec
                                      Primary LCR

                                     • Primary FML

                                      Secondary LCR

                                     • Secondary FML



                                      Clay Liner
                                      Native Soils
                Unsaturated Zone

                ; Saturated Zone
                r//////j0m!(f0(m
"Minimum hydraulic conductivity is now 1 cm/sec.

Figure 3-3. Profile of MTG double liner system.


therefore to select polymers for  FML construction
with care. Chemical compatibility, manufacturing
considerations, stress-strain characteristics, sur-
                                                     28

-------
vivability, and permeability are some  of the key
issues that must be considered.

Chemical Compatibility
The chemical  compatibility of a FML with waste
leachate is an important material consideration.
Chemical compatibility and EPA Method 9090 tests
must be performed on the synthetics that will be
used to construct FMLs. (EPA Method 9090 tests are
discussed  in more detail  in Chapter Nine.) Unfor-
tunately, there usually is a lag period between the
time these tests are performed  and the actual
construction of a facility. It is very rare  that at the
time of the 9090 test, enough material is purchased
to construct the liner. This means that the material
used for testing  is not typically  from the same
production lot as the synthetics installed in the field.

The molecular structure of different polymers can be
analyzed through differential scanning calorimeter
or thermogravimetric testing. This testing or
"fingerprinting" can ensure that the same material
used for the 9090 test was used in the field. Figure 3-
4 was provided by a HOPE manufacturer, and the
fingerprints depicted are all from high density
polyethylenes. Chemical compatibility of extrusion
welding rods  with polyethylene  sheets is also  a
concern.

Manufacturing Considerations

Polyethylene sheets are produced in various ways:

•  Extrusion—HOPE
•  Calendaring—PVC
•  Spraying—Urethane

In general, manufacturers are producing  high
quality polyethylene  sheets.  However,  the

Table 3-1. Basic Composition of Polymeric Geomembrane
                                    180°C, SOOpsig
      28-

      24-

      20-

   LL
   to  12-1
   0)

       8-
         0  10 20  30  40  50 60 70 80  90 100110120

                        Time (min)

 Figure 3-4. Comparison of "fingerprints" of exothermic peak
          shapes.
compatibility of extrusion welding rods and high
density polyethylene sheets can be a problem. Some
manufacturing processes can cause high density
polyethylene to crease. When this material creases,
stress fractures will result. If the material is taken
into  the field to be placed,  abrasion damage  will
occur on the creases. Manufacturers have been
working to resolve this problem and, for the most
part, sheets of acceptable quality are  now being
produced.

Stress-Strain Characteristics

Table 3-2 depicts typical mechanical properties of
HDPE, CPE, and  PVC. Tensile strength is a
                                                          Composition of Compound Type
                                                               (parts by weight)
Component
Polymer or alloy
Oil or plasticizer
Fillers:
Carbon Black
Inorganics
Antidegradants
Crosslinking system:
Inorganic system
Sulfur system
Crosslinked
100
5-40
5-40
5-40
1-2
5-9
5-9
Thermoplastic
100
5-55
5-40
5-40
1-2
-
' Semicrystalline
100
0-10
2-5
1
'-- .,
Source: Haxo, H. E. 1986. Quality Assurance of Geomembranes Used as Linings for Hazardous Waste Containment. In: Geotextiles and
      Geomembranes, Vol. 3, No. 4. London, England.
                                                29

-------
fundamental design consideration. Figure 3-5 shows
the uniaxial stress-strain performance of HDPE,
CPE, and PVC. As 600, 800,1,100, and 1,300 percent
strain is developed, the samples fail. When biaxial
tension is applied to HDPE, the material  fails at
strains less than 20 percent. In fact, HDPE can fail at
strains much less than other flexible  membranes
when subjected to biaxial tensions common in the
field.

Another stress-strain consideration is that high
density polyethylene, a material used frequently at
hazardous waste facilities, has a high degree of
thermal coefficient of expansion - three to four times
that of other flexible membranes. This means that
during the course of  a  day (particularly in the
summer),  100-degrees-Fahrenheit (°F) variations in
the temperature of the sheeting are routinely
measured. A 600-foot long panel, for example, may
grow 6 feet during a day.


Survivability

Various  tests may be used to  determine the
survivability of unexposed polymeric geomembranes
(Table 3-3).  Puncture tests frequently are  used to
estimate 'the survivability of FMLs in the field.
During a puncture test, a 5/16 steel rod with rounded
edges is pushed down through the membrane. A very
flexible membrane that has a high strain capacity
under biaxial tension may  allow that rod to
penetrate almost to the bottom of the chamber
rupture.  Such  a membrane has  a very  low
penetration force but a very high penetration elonga-
tion, and may have great survivability in the field.
High density polyethylenes will give  a very high
penetration force, but have very high brittle failure.
Thus, puncture data may not properly predict field
survivability.


Permeability

Permeability of a FML is evaluated using the Water
Vapor Transmission test (ASTM E96). A sample of
the membrane is placed on top of a small aluminum
cup containing a small amount of water. The cup is
then placed in  a  controlled  humidity  and
temperature chamber. The humidity in the chamber
is typically 20 percent relative humidity, while the
humidity in  the  cup is 100  percent.  Thus,  a
concentration  gradient is set  up  across the
membrane. Moisture diffuses through the membrane
and with time the liquid level in the cup is reduced.
The rate at which moisture is moving through the
membrane  is measured. From that rate,  the
permeability of the membrane is calculated with the
simple diffusion equation (Pick's first law).  It is
important to  remember that  even if a  liner is
installed correctly with no holes, penetrations,
punctures, or defects, liquid will still diffuse through
the membrane.                 '•

Design Elements
A number of design elements must be considered in
the construction of flexible membrane liners: (1)
minimum technology  guidance,  (2)  stress
considerations, (3) structural details, and (4) panel
fabrication.

Minimum Technology Guidance
EPA has set minimum technology  guidance for the
design of landfill and surface impoundment liners to
achieve de minimis leakage. De minimis leakage is 1
gallon per acre per day. Flexible membrane liners
must be a minimum of 30 mils thick, or 45 mils thick
if  exposed for  more than 30  days.  There  may,
however, be local variations in the requirement of
minimum thickness, and these variations can have
an impact on costs. For example,  membranes cost
approximately $.01 per  mil per square foot, so that
increasing the required thickness of the FML from
30 mils to 60 mils, will increase the price $.30 cents
per square foot or $12,000 per acre.
                              I
Stress                        I
Stress considerations must be considered for side
slopes and the bottom of a landfill. For side slopes,
self-weight (the weight of the membrane itself) and
waste settlement must be considered; for the bottom
of the facility, localized settlement and  normal
compression must be considered.  !

The primary FML must be able to support its own
weight on the side slopes. In order to calculate self-
weight,  the FML specific gravity, friction angle,
FML thickness, and FML yield stress must be known
(Figure  3-6).                   ;

Waste settlement is another consideration. As waste
settles in the landfill, a downward force will act on
the primary FML. A low friction component between
the FML and underlying material prevents that
force from being transferred  to  the underlying
material, putting tension on the primary FML. A 12-
inch direct shear test is used to measure the friction
angle between the FML and underlying material.

An example of the effects of waste settlement can be
illustrated by a recent incident at a hazardous waste
landfill  facility in California. At this facility, waste
settlement led to sliding of the  waste, causing the
standpipes (used to  monitor secondary leachate
collection sumps) to move 60 to 90 feet downslope in
1  day. Because there was a very low coefficient of
friction between the primary liner and the geonet,
the waste (which was deposited in a canyon) slid
down the canyon. There  was  also a failure zone
between the secondary liner and the clay. A two-
                                               30

-------
 Table 3-2. Typical Mechanical Properties

Density, gm/cm3
Thermal coefficient of expansion
Tensile strength, psi
Puncture, Ib/mil
HOPE
>.935
12.5 x 10-5
4800
2.8
CPE
1.3 - 1.37
4 x 10-5
1800
1.2
PVC
1 .24 - 1 .3
3x10-5
2200

      4000
                                                                                    To 3860 PSI at 1180%
                     100
                                 200
                                             300
                                          Strain, %
      400
                   500
 Figure 3-5. FML stress-strain performance
          (uniaxial-Koerner, Richardson; biaxial-Steffen).
dimensional slope stability analysis at the site
indicated a factor of safety greater than one. A three-
dimensional slope  stability analysis, however,
showed the safety factor had dropped  below one.
Three-dimensional slope stability analyses  should
therefore be considered with canyon and  trench
landfills.


Since more trenches are being used in double FML
landfills, the impact of waste settlement along such
trenches should be considered. Figure 3-7 is a simple
evaluation of the impact of waste settlement along
trenches on the FML.  Settlements along trenches
will cause strain in the membrane, even if the trench
is a very minor ditch.  Recalling that when biaxial
tension is applied to high density polyethylene, the
material fails at a 16  to 17 percent strain, it is
possible that the membrane will fail at a moderate
settlement ratio.

Another consideration is the normal load placed on
the membranes as waste is piled higher. Many of the
new materials on the market, particularly some of
the linear low density polyethylene (LLDPE) liners,
will take a tremendous amount of normal load
without failure. The high density polyethylenes, on
the other hand,  have a tendency to  high brittle
failure.

Structural Details
Double liner systems are more prone to defects in the
structural  details (anchorage, access ramps,
collection standpipes, and penetrations) than single
liner systems.
                                                31

-------
Table 3-3. Test Methods for Unexposed Polymeric Geomembranes
Membrane Liner Without Fabric Reinforcement
Property
Analytical Properties
Volatiles

Extractables

Ash
Specific gravity
Thermal analysis:
Differential scanning
calorimetry (DSC)
Thermogravimetry
(TGA)
Physical Properties
Thickness - total
Coating over fabric
Tensile properties
Tear resistance
Modulus of elasticity
Hardness
Puncture resistance
Hydrostatic resistance
Seam strength:
In shear
In peel
Ply adhesion


Environmental and Aging
Effects
Ozone cracking
Environmental stress
cracking
Low temperature testing
Thermoplastic

MTM-1a

MTM-2a

ASTM D297, Section 34
ASTM D792, Method A


NA
Yes

ASTM D638
NA
ASTM D882,
ASTM D638
ASTM D1004
(modified)
NA
ASTM D2240
Dura A or D
FTMS101B,
Method 2065
NA

ASTM D882, Method A
(modified)
ASTM D413, Mach
Method Type 1
(modified)
NA




ASTM D1149
NA

ASTM D1790
Crosslinked

MTM-1a

MTM-2a

ASTM D297, Section 34
ASTM D297, Section 15


NA
Yes

ASTMD412
NA
ASTM D412
ASTM D624
NA
ASTM D2240
Duro A or D
FTMS 101B,
Method 2065
NA

ASTM D882, Method A
(modified)
ASTM D413, Mach
Method Type 1
(modified)
NA




ASTM D1 149
NA

ASTM D746
Semicrystalline

MTM-ia

MTM-2a

ASTM D297, Section 34
ASTM D792, Method A

\/r\ff
Yes
Yes

ASTM D638
NA
ASTM D638
(modified)
ASTM D1004
DieC
ASTM D882, Method A
ASTM D2240
Duro A or D
FTMS 1 01 B,
Method 2065
ASTM D751, Method A

ASTM D882, Method A
(modified)
ASTM D41 3, Mach
Method Type 1
(modified)
NA




NA
ASTM D1 693

ASTM D1790
ASTM D746
Fabric Reinforced
,
MTM-ia
(on selvage and
reinforced sheeting)
MTM-2a
(on selvage and
reinforced sheeting)
ASTM D297, Section 34
(on selvage)
ASTM D792, Method A
(on selvage)
>
MA '
IMr\ ,
Yes

ASTM D751, Section 6
Optical method
AStM D751, Method A
and. B (ASTM D638 on
selvage)
ASTM D751, Tongue
method (modified)
NA
ASTM D2240 Duro A
or 0 (selvage only)
FTMS 1.01 B,
Methods 2031 and 2065
ASTM D751, Method A

ASTM D751, Method A
(modified)
ASTM D413, Mach
Method Type 1
(modified)
ASTM D413, Mach
Method Type 1
ASTM D751 , Sections
39:42


ASTM D1 149
NA

ASTM D2136
Tensile properties at
  elevated temperature

Dimensional stability
ASTM D638 (modified)     ASTM D412 (modified)    ASTM D638 (modified)    ASTM D751 Method B
                                                                   (modified)
ASTM D1204
                       ASTM D1204
                                             ASTM D1204
                                                                   ASTM D1204
                                                       32

-------
Table 3-3. Test Methods for Unexposed Polymeric Geomembranes (continued)




                                       Membrane Liner Without Fabric Reinforcement
Property Thermgplastc Crosslinked ; Semicrystalline Fabric Reinforced
Air-oven aging ASTM D573 (mod fied) ASTM D573 (modified) ASTM D573 (modified) ASTM D573 (modified)
Water vapor transmission ASTM E96, Method BW ASTM E96, Method BW ASTM E96, Method BW ASTM E96, Method BW
Water absorption ASTM D570 ASTM D471 ASTM D570 ASTM D570
Immersionin standard ASTM D471, D543 ASTM D471 ASTM D543 ASTM D471 D543
liquids '
Immersion in waste
^uids EPA 9090 EPA 9090 EPA 9090 EPA 9090
Soil burial ASTM D3083 ASTM D3083 ASTM D3083 ASTM D3083
Outdoor exposure ASTM D4364 ASTM D4364 ASTM D4364 ASTM D4364
Tub test b b b b
aS
"S
Nf
So

ee reference (8).
ee reference (12).
^ = not applicable.
urce: Haxo, 1987

Cell Component: FLEXIBLE ME.MBRAWE Lmep
Consideration !~Ttw*'LE ^TRE« - LIUER UEIGHT • t™ u»,e
A5ILITY OF FML TO zureaHT
Required Material Properties Range
F«i<=-n<>u £>"<;Lf-
• FML-TO-LCE ^ %L \°~-,. *<>'
FML TiWuijti-i ,-t to TO no
Oilli1 MIC limi," "£*':> > ^Y I««ero5»o
Analysis Procedure:
"" lifer1


(4U^-u«. D«,«M aoi. SimA~
PR. GI /s
Design Ratio: Referenc
T* OKJ U ^JCi^HT ow THE
Test Standard
Oi«££T -5HCAA PftoPoato ASTM
0 "Te^jsue A-STM Dtss

>-' l'x t
-)ffY
es:

FML ^rtc.Fii <^«»uily , Cj. O.S4I
• p>- 5D*
(O tfr.ucj^j^jt FML TtU4iLt foeZ(TE T
•°'° 1
= 2.2.2. Ib/fr
T' ~\o.e, ^.vj -J0°_ 22.2
(z1 ^^LcuL^Tt FMI_ lei_,-5at STRESS s"
..,VO,^;¥,,,
'te~
20 ' 450 /"./ •.
»« -'*-/'*- '« o^
Example No. 5.H
 Figure 3-6.  Calculation of self-weight.
                                                       33

-------
                          0.1          0.2
                         Settlement Ratio, S/2L
Figure 3-7. Settlement trough models (Knipschield, 1985).
Anchorage
Anchor trenches can cause FMLs to fail in one of two
ways: by ripping or by pulling out. The pullout mode
is easier to correct. It is possible to calculate pullout
capacity for FMLs  placed in  various  anchorage
configurations (Figures 3-8 and 3-9).  In  the "V;"
anchor configuration, resistance can be increased by
increasing the "V" angle. A drawback to using the
"V"  design for getting an accurate estimate of
pullout  capacity  is that it uses more  space. The
concrete trench is not presently used.


Ramps
Most facilities have access ramps  (Figure 3-10),
which are used by trucks during construction and by
trucks bringing waste into the facility.  Figure 3-11
depicts a cross section of a typical access ramp. The
double FML integrity must be  maintained over the
entire surface of the ramp. Because ramps can fail
due  to  traffic-induced sliding,   roadway
considerations, and drainage, these three factors
must be considered  during  the design and
construction of access ramps.

The weight of the  roadway, the weight of a vehicle on
the roadway, and the vehicle braking force all must
be considered when evaluating the potential for
slippage due to traffic (Figure 3-12). The vehicle
braking force should be much larger than the dead
weight of the vehicles that will use it. Wheelloads
also have an impact on the double FML system and
the two leachate collection systems  below the
roadway. Trucks with maximum axle loads (some
much higher than the legal highway loads) and 90
psi tires should be able to use the ramps. Figure 3-13
illustrates how to verify that wheel contact loading
will not damage the FML. Swells or small drains
may be constructed  along the inboard side  of  a
roadway to ensure that the ramp will adequately
drain water  from the roadwjay. Figure 3-14
illustrates how to verify that a ramp will drain water
adequately. The liner system, which  must be
protected from tires, should be armored in the area of
the drainage swells. A sand subgrade contained by a
geotextile beneath the roadway can prevent local
sloughing and local slope failures along the side of
the roadway where the drains are located. The sand
subgrade tied together with geotextile layers forms,
basically,  800-foot long sandbags stacked on top of
one another.

Vertical Standpipes
Landfills have two leachate collection and removal
systems (LCRSs): a primary  LCRS and a secondary
LCRS. Any leachate that penetrates the primary
                                                34

-------
Cell Component: FLEXIBLE ME.KI&RAJ-JE
Consideration* ^ ^"" '^""^•'iS -CALCULATE

Required Material Properties Range
•^•IL/FML Fw^n«u Au^ie. 12-20*
• S.iL F«i<=Tiou AuqL6 2S-J8"
Dull "1C Mnrun
Analysis Procedure:
* iC^toMETKV * MA.T*IR IAL,
- SLOPE At-i^lE fe -SoiL fd
-ENBePMtMr Lcu?-s.^r



Standard
A»TS, P«0P0«0
<•
I V
LvJfj -i


Design Ratio: References:
MOT APPLICABLE.
Example:
^iv/E M *• ^EoMtTR V 5^, L
• DR« 1.5. M.^.M-JM
(0 DtFiuE^piA6LE.^ /^ iw" U'
-s^\+ t«*
^^ ^--X,«JM'«"«*.M-P-
H - ' •) T 21"«6XTAMll' -Jglt/
	 b!I*.U\ ^ 1 I.SixlB.V-S.ulM'TA,UIS* "1° ^*"T
- ., x" — ' 'W""Av*' /-i/.|'

1 ^ ^^^ ^J.^
"d*"'-*l'M'5 7,3-q^r 4»-i- '"•''•'"]
T |.331 3Hlb/Fr
0,U«E1f A.^B.« _x^ «^"*W*
'"t''*'rt''^Ll»-J..^)"1\.
l-aai ^^ /'T
--^^•-••^^^^^^^^^
KP =="
[T]<° '•-•*•'
Example No. 2>.17
Figure 3-8. Calculation of anchor capacity.
system and enters the secondary system must be
removed.   Vertical  standpipes  (Figure  3-15) are
used to access the primary leachate collection sumps.
As waste settles over time, downdrag forces can have
an impact on standpipes. Those downdrag forces can
lead to puncture of the primary FML beneath the
standpipe. Figure 3-16 illustrates how to verify that
downdrag induced settlement of standpipes will not
cause  the underlying leachate collection  system  to
fail.

•To reduce the amount of downdrag force on the waste
pile, standpipes can be coated with viscous or low
friction coating. Standpipes can be encapsulated
with multiple layers of HDPE. This material has a
very low coefficient of friction that helps reduce the
amount of downdrag force on the  waste piles. Figure
3-17  illustrates how to evaluate the  potential
downdrag forces acting on standpipes and how  to
compare coatings for reducing these forces.
Downdrag forces also affect the  foundation or
subgrade beneath the standpipe. If the foundation is
rigid, poured concrete, there is a potential for sig-
nificant strain gradients. A flexible foundation will
provide a more gradual transition and spread the
distribution of contact pressures  over a larger
portion of the FML than will a rigid foundation
(Figure 3-18).  To  soften rigid  foundations,
encapsulated steel plates may be installed beneath
the foundation, as shown in Figure 3-15.

Standpipe  Penetrations
The secondary leachate collection system is accessed
by collection standpipes that  must penetrate the
primary liner. There  are two  methods  of making
these penetrations: rigid or flexible (Figure 3-19). In
the rigid penetrations, concrete anchor blocks are set
behind the pipe with the membranes anchored to the
concrete. Flexible penetrations are preferred since
these allow the pipe to move without damaging the
                                                35

-------
                 Tcosg
Cover Soil
                            mrnTiF iTrnrnT
                       tsinp
                                                 ^  < *L
                                                            <},= Ycs^cs
                                   Horizontal Anchor
                                   "V" Anchor
                  Tcosp
                       tsing
                                    Concrete Anchor
Figure 3-9. Forces and variables—anchor analysis.
liner. In either case, standpipes should not be welded
to the liners. If a vehicle hits a pipe, there is a high
    potential for creating major tears in the liner at
    depth.
                                   36

-------
Ramp structure
Figure 3-10. Geometry of typical ramp.
                                                   FML—•
                                                   FML—•
                                                                  18' Typical
 Figure 3-11. Cross section of typical access ramp.


Wind Damage
During the installation of FMLs, care must be taken
to avoid damage from  wind. Figure  3-20 shows
maximum wind speeds  in the United  States.
Designers should determine if wind will affect  an
                                                37

-------
Cell Component: RA.MP
Consideration: -^UD'Sj<:\ ' -"g-a-Ff THAT RAMP -sj6-&A-sE. •»
5TA8L6 JUPE.R LOAD,
Required Material Properties
S.IL • PML fa.cr— j Au^u, $fnl.
Dull Kit ««nn
Analysis Procedure:

Range
to - IS'
14 • «*
\o-ia'
^.-ivj" V
Test

^3^=4
Standard
«TM RoRrrfO
^
fa * rrt ie.T.»»ML FtRe£ (Q pA*£ o r K OAOVI A v
* C W^^ U*4 ) V ^tf < ft 1* TAtJ 2
UMEAE ,£M.U i»7fie MIMIMJH fc'^r.^j norec?FA^e. AM^LE
(^ • KoHt^iou FoRiE
i«r*,~t Dt*^(?AT,»,DR


^rt (?E*i5Tluq R>R«:e-b

WK" (U^W^'^^e,
Design Ratio:
B«»M- «/
rt
References:
Example:
**iL-L«iR JJ" Zoa,p»f?
TML-I^O; 11° o ! ^ 	 fiuOat e« irtaiA
UIM-" . i»' Itu^rw • 1*°' THKKUEW £4" ft- 8°
U.-iJ^r.rBp.^ -;^"*'^^- •*fa-"" ft*1^
F8' &^A.«,U, R.^6 - .9*n»K,P- i|.K,p
, r
F^» (7o2 4 no) *CQ<» £>° + TXkj 12°
r ITo,^ Kip-^
O1P*FM-IE pE,-»^KJ R^T.o*^ pf^

^^ l"70.«l 17**.^
^E
-------
 Cell Component: I? A.MP-
 Consideration: WHt£L
                       g - VER.FI
 Required Material Properties  Range    Test   Standard
                          2.S - 40'
 Analysis Procedure:
 (0
          PR --
 Design Ratio:

 PRMIPJ 5>° <9|
References:
                                                   Example:
                                                          lUfc F'ELP 6.KJTA
                                                                    .? 6..?
                                                                                          
-------
Cell Component:
Consideration t
Required Material Properties
 lu-piAjji  now -r i-tre  , £
 Pl«MlA6iur»,K)flF'S
                                                                                     1*3
                                                                CO E-S.TIM1AT6- F^o1^ f^APAiiTY «r LCC
                                                                                                  1.2 fi^ -sit.
                                                                                                         |S
                                                                                                        Example No. 4.2.
Figure 3-14. Calculation of ramp drainage capability.
                                                            40

-------
Placing low friction HOPE around a standpipe.
                                                               41

-------
                     Steel Plate    &.  .
                       •  ^        f!f)  *—
                                                      36"-48" RCP
                                                              •*	+•
                                                     Concrete Base
                                                                              Gravel
                       FML

                                                                                                        ,LCR
                                                                                               Sand
Figure 3-15. Details of standpipe/drain.
                                                          42

-------
Figure 3-16., Verification that downdrag induced settlement will not cause LCR failure.
                                                        43

-------
 Cell  Component: STXUDP.PE.
                                              fof*. REOJ^-nwo of
 Required Material  Properties
 Range
                                            Test
                                                    ASTM PROPOSED
                    Standard
 Analysis Procedure:
            P»UUpgA<^ WiTHouT.
                                                 (MWFAtf DM7.2*)
 'tf> STALJOPJ>e  PffUlMOftAC^ U*TH &lT»lHtM
 Design Ratio:
References:

  V6«cC".T7,

  (J*vr-/v«  PM T.l ( 1^82)
                                  Example:
                                                                             - DIAMETER , D - ^ O"


                                                                             - PfcPTH 2 »  |£S'
                                                                               C MfeotUM




                                                                   CO STA.MPPIPE  Poukj
                                                                             - 655 kifi
Figure 3-17.  Evaluation of potential downdrag forces on standpipes with and without coating.
                                                                                                  a .73
                                                                                                  5
                                                                                                      —i_ALL PILCS<

                                                                                                       1  I  t
                                                                                                      .VW SOTT.
                                                                                                      rrr*>":±
                                                                                                                      RATIO OF

                                                                                                                       CA/C
                                                                                                     oCLC
                                                                                                         Example No.
                                                             44

-------
           •s
           J
           111
                2.0
                                                                           edge

                                                                           1.0
                                                  A) Elastic Settlement Constant
            r/a
                                                           Clay Subgrade
Sand Subgrade
                                                                            (after Terzaghi and Peck)
                     Elastic Subgrade
                                             B) Distribution of Contact Pressures
Figure 3-18.  Standpipe induced strain in FML.
                                                            45

-------
                                Geotextile
   Weld
              FML
   Steel Clamp     [

       Pipe Sleeve

                Weld
                        Rigid Penetrations
Flexible Penetrations
                  Weld
                           Pipe Sleeve

  ygBBisagBEaM*.	/..... •  -.
   \            -Pipe              '  1 Geotextile
                                                 FML
                        •Pipe
                  Primary FML
             Weld i
                                                                                               Secondary FML
Figure 3-19. Details of rigid and flexible penetrations.
                                                         46

-------
Figure 3-20.  Design maximum wind speeds.
                                                       47.

-------
Cell Component: FU^.euL Me.Me.RAue.
p -1J . UllUO L,CT: • 7.3/)o.£>^ 073 we,
o FT =*• 5-"7/'o.o = 0.57 fjq
Example No. &>.!
Figure 3-21. Calculation of required sandbag spacing for FML/FMC panels.
Table 3-4. Wind-Uplift Forces, PSF (Factory Mutual System)
Height
Above "
Ground _
(ft)
0-15
30
50
75
Wind Isotach, mph :
City, Suburban Areas, Towns,
70
10a
10
12
14
SO
11
13
15
18
90
14
17
19
22
and Wooded Areas
100
17
21
24
27
110
20
25
29
33
Flat, Open Country,
70
14
16
18
20
80
18
21
24
26
or Open Coastal Belt > 1500 ft from Coast
90
23
27
30
33
•I 00
29
33
37
40
; 110
35
40
; 44
49
120
14
48
35
85
'Uplift pressures in PSF
                                                         48

-------
 Cell Component:  Fi.eyi6Le  MEMBBAME  LIUI
                                          L Art<> v
                                         IM F~M L .
 Required Material Properties   Range     Test    Standard
 S.,L^e>»-.FML
  FML-LCE  Faic
 Yieio STRESS oF
 Drill UIC Unrxm
 Analysis Procedure:
  EXAMPLE:
 Design Ratio:
  \o-Zo'
  a -is°
 iooo-tZ6t>\
                     A.XTM 04J0
                                       =  ISoo p«t
References:
                                                                 Example':
                                                                   •SOLVE  Fog Snoiug STABILITY
                                                                                           pj,- loo»«2.4« stJS* ' SfcS l
                                                                  ." SOLVE Foa MfcMftRfcME ~feKJ*'°M
                                                                                         - ISooox
                                                                           Bur
                                                                                                    .'.  T»  O
                                                                            lkjCE  1 -O
                                                                                                       (Example No.  3.18
Figure 3-22.  Calculation of soil cover stability.
                                                            49

-------
Creation of "whales."
                                                             50

-------
            -Liner
. Geotextile or
 Drainage Composite
                                          Place Vent Higher than Maximum Liquid Level
                                          at Over-Flow Conditions  ',

                                           Two-Inch Minimum
                                                                      Wind Cowl Detail
                                      Gas Flow
                     Openings in Vent to be Higher than
                    "Top of Berm or Overflow Liquid Level
            Geotextile or
            Drainage Composite
                                        Air/Gas Vent Assembly
                               — Approx. Six-Inches



                                       Bond Skirt of Vent to Liner


                                      Gas Flow
                                                                                                        Geomembrane
Concrete
Figure 3-23.  Gas vent details.
                                                           51

-------
                                                                 A      A        A
7C
N /o^\
\ *£y
\
(2§)
(26)
©

/§\S—
i i '
I I i
i i

^» Toe of Slope /^
i
0
r~ T "~i T T i
i . ' . i © ' ®
i i i
%1
f
©
©
©

©\
                                                                 A      A        A
                                             ^^  Panel Number
                                             /\  Seam Number
Figure 3-24.  Panel-seam identificaiton scheme.
                                                       52

-------
   4.  ELEMENTS OF LIQUID MANAGEMENT AT WASTE CONTAINMENT
                                            SITES
Introduction
The drainage system for removing leachate or other
aggressive liquids from landfills, surface impound-
ments, and waste piles is critically  important. Even
if a liner has no leaks, the phenomenon of molecular
diffusion will allow some of the organics from the
liquids ponded on top of the liner  system to leach
through the  flexible membrane liner and the clay.
The timely collection and removal of that leachate is
at the heart of this chapter.

This chapter presents an overview of collector design
and materials, followed by a discussion of the three
parts  of a  liquid management system: the leachate
collection and removal system above the primary
liner,  the  secondary leak detection collection  and
removal system between the primary and secondary
liners, and the surface water collection system above
the closure of the completed facility. The chapter
concludes  with a discussion of gas collector  and
removal systems. The  following topics will be
examined:

• Overview
    Drainage Materials
    Filtration Materials
    Geosynthetics
    Design-by-function Concepts

• Primary  Leachate Collection and Removal
  (PLCR)  Systems
    Granular Soil (Gravel) Drainage Design
    Perforated Collector Pipe Design
    Geonet Drainage Design
    Granular Soil (Sand) Filter Design
    Geotextile Filter Design
     Leachate Removal Systems

• Leak Detection, Collection, and Removal (LDCR)
  Systems
    Granular Soil (Gravel) Drainage Design
     Geonet Drainage Design
     Response Time
     Leak Detection Removal Systems

• Surface Water Collection and Removal  (SWCR)
  Systems
• Gas Collector and Removal Systems

Overview
Leachate refers to rainfall and snowmelt that
combines  with liquid  in  the  waste  and
gravitationally moves to  the bottom of a landfill
facility. During the course of its migration, the liquid
takes on the pollutant characteristics of the waste
itself. As such, leachate is both  site specific and
waste specific with regard to both its quantity and
quality. The first part of the collector system to
intercept the leachate is the primary leachate
collection and removal  (PLCR) system located
directly below the waste  and above the primary
liner. This system must be designed and constructed
on a site-specific basis to  remove the leachate for
proper treatment and disposal..

The second part  of a  leachate collection system is
between the primary and secondary liners.  Varying
with State or region, it is called by a number of
names including  the secondary leachate collection
and removal (SLCR) system, the leak detection
network, or the leak questioning system. It will be
referred to here as the leak detection, collection, and
removal (LDCR)  system. The main purpose of this
system is to determine the degree of leakage, if any,
of leachate through the primary liner. Ideally, this
system would collect  only  negligible quantities of
leachate; however, it must be designed on the basis of
a worst-case scenario.

The third part, called the  surface water collection
and removal (SWCR) system, lies above the waste
system in a cap or closure above the closed facility.
Its purpose is to redirect surface water coming
through the cover soil from off of the  flexible
membrane in the cap to the outside perimeter of the
                                               53

-------
system. The location of all three parts of the liquid
management system is illustrated in Figure 4-1.

Drainage Materials
The drainage materials for the liquid management
system must allow for unimpeded flow of liquids for
the intended lifetime of the facility. In a leachate
collection system, the drains may consist of pipes,
soil (gravel),  geonets, or geocomposites. These
materials will be described in the following sections.

Perforated drainage pipes have the advantage of
common usage and design, and they transmit fluids
rapidly. They do, however,  require considerable
vertical space, and are susceptible to particulate
clogging, biological clogging,  and creep (deflection).
Creep is of concern for both poly vinyl chloride (PVC)
and high density polyethylene (HDPE) pipe
materials.

According to proposed EPA  regulations,  the
hydraulic conductivity value for soil  used as  the
drainage component of leachate  collection systems
will increase over previous regulations by two orders
of magnitude, from 0.01 cm/sec to I cm/sec, in the
very  near future. This  regulation essentially
eliminates the use of sand, and necessitates the use
of gravel. Gravel  that meets this  regulation  has
particle sizes of 1/4 to 1/2  inches and must be quite
clean with no fines content. While  gravels of this
type  are durable and  have! high hydraulic
conductivities, they require a  filter soil to protect
them. They also tend to move when waste is loaded
onto the landfill or personnel walk on them. For the
latter reason, they are practically ^mpossible to place
on side slopes.                 ',


The synthetic materials that best1 meet inplane flow
rate regulations are called geonets. Geonets require
less space than perforated pipe or gravel, promote
rapid transmission of liquids, and, because of their
relatively open apertures, are less likely to clog.
They  do, however, require geotextile filters above
them  and can experience problems  with creep and
intrusion. Geonets have the disadvantage of being
relatively new and, therefore, less familiar to owners
and designers than are sand  and gravel drainage
materials.
                               -tf"—&
                                         Cover Soil
                            T°\~*g                cwc—-        —...	,
                                                            ^^
                                                                        ^
 Figure 4-1.  The three elements of a liquid management drainage system in a double-lined solid waste facility.
                                                54

-------
Another new synthetic material is called a drainage
geocomposite, many types of which are available.
Geocomposites have most of the same  advantages
and disadvantages of geonets. They generally are not
used for primary or secondary  leachate collection
systems, however,  because of their relatively low
crush strength. The  crush strength, or normal
strength perpendicular to the plane, of currently
available  products is not sufficient to carry the
weight of a large landfill. Geocomposites are useful,
however, for surface water collector systems, where
the applied normal stresses are quite low.

Filtration Materials
The openings in drainage materials,  whether holes
in pipes, voids in gravel, or apertures in geonets,
must be protected  against invading fine particle-
sized materials.  An intermediate material,  having
smaller openings than those of the drainage
material, must be used as a filter. Commonly in a
pipe or gravel drain, a medium-coarse to fine sandy
soil is used as a filter.  Sand, however, has the
disadvantages  of  taking up vertical space and
moving under various loading conditions.

Geotextiles used as filters avoid these problems. The
open spaces in the fabric allow liquid flow while
simultaneously  preventing upstream fine particles
from fouling the drain. Geotextiles save vertical
space,  are easy to install, and have the  added
advantage of remaining stationary under load. As
with sand filters, clogging can occur, and because
geotextiles are a new technology much about them is
not known. Geotextiles are being used more and
more not only for filters, but also as cushioning
materials above and/or below FMLs.

Geosynthetics
Geosynthetic materials play a key  role in  liquid
management systems. The five major categories of
geosynthetics are:

•   Geotextiles
•   Geogrids
•   Geonets
•   Geomembranes
•   Geocomposites

A brief discussion of each type follows.

Geotextiles are either woven or nonwoven  fabrics
made from polymeric fibers. Woven geotextiles are
fabrics made up  of webbed fibers that run in
perpendicular directions. For filtration, the spaces
between the fibers  are the most important element.
These spaces or voids must be large enough to allow
unimpeded liquid flow but be small enough to keep
out invading particulates. The geotextiles also must
be sufficiently strong to cover and reinforce the
apertures, or openings, of the drainage materials
they are meant to protect.

In nonwoven geotextiles the fibers are much thinner
but far more  numerous.  The various types are
needle-punched, resin-bond, and melt-bond. All
contain a labyrinth of randomly oriented fibers that
cross one another so that there is no direct line of
flow. The fabric must have enough open space to
allow liquid to pass through,  while  simultaneously
retaining any upstream movement of particles. The
needle-punched nonwoven type is very commonly
used as a filter material.

Geogrids are very  strong in  transverse and
longitudinal directions,  making them useful as
reinforcing materials for either soil or  solid waste.
Generally, they are used to steepen the side slopes of
interior cells or exterior containment slopes of a
facility. Recently they also have been  used in the
construction of "piggyback" landfills, i.e., landfills
built on top of existing landfills, to reinforce the
upper landfill against differential settlements within
the lower landfill.

Geonets are formed with intersecting ribs made from
a counter-rotating  extruder. A  typical geonet is
about 1/4-inch thick from the top of the  upper 'rib to
the bottom of the lower rib, yet the flow capability is
approximately equivalent to that of 12 inches of sand
having a 0.01  cm/sec  permeability. (The proposed
regulation will increase this value to 1 cm/sec, as
mentioned earlier.)  The rapid transmission rate is
due to clear flow paths in the geonets, as opposed to
particle obstructions in a granular soil material.
There are two main concerns with geonets. First, the
crush strength at the rib's intersection must be
capable of maintaining its  structural stability
without excessive deformation or creep. Second,
adjacent materials must be prevented from intruding
into the rib apertures, cutting off or reducing flow
rates.

Foamed geonets are relatively new  products made
with a foaming agent that produces a thick geonet
structure (up to 1/2-inch) with very high flow rates.
These improved flow rates result from the thicker
product, but eventually the nitrogen gas in the rib
voids diffuses through the polymer structure, leaving
behind a structure with reduced thickness. The
result  over  the long  term is a solid rib geonet
thickness equivalent to other nonfoamed geonets.

The fourth type of geosynthetic is a geomembrane, or
FML. It is the primary defense against escaping
leachate and of crucial importance. FMLs are the
focus of Chapter Three.
                                                55

-------
The final category of geosynthetics is drainage,
geocomposites. These are polymeric materials with
built-up columns, nubs, cuspations, or other
deformations that allow planar flow within their
structure. A drainage geocomposite having 1-inch
high columns can carry the flow -of a 4- to 5-inch
diameter pipe. Many products, however, have low
crush  strengths that are  inadequate for deep
landfills or surface impoundments. They are useful,
however, for surface water collector systems above
the closed facility where they only need to support
approximately  4 feet  of soil and  construction
placement equipment.

Design-by-function  Concepts
Whatever parameter of a specific material one is
evaluating, a required value for the material must be
found using a design model and an allowable value
for the material must be determined by a test
method. The allowable value divided by the required
value yields the design ratio (DR), or the resulting
factor of safety (FS). This design-by-function concept
is necessary to design and evaluate new materials
that are both feasible  and safe for  a  variety of
situations.

In evaluating drainage and filtration materials, an
allowable flow rate is divided by a required flow rate
to obtain the design ratio or factor of safety according
to the equations below:

(a) For Drainage:

               DR = qallow/qreqd              (D
                or

               DR = Va
    where  DR = design ratio

           q   = flow rate per unit width

           V  = transmissivity
(b) For Filtration:
DR = qallow/qreqd
or

DR =
                                             (4)
    where DR = design ratio
           q   = flow rate per unit area
           W  = permittivity

Transmissivity is  simply  the coefficient of
permeability, or the hydraulic conductivity  (k),
within the plane of the material multiplied by the
thickness  (t)  of  the material.  Because  the
compressibility of some polymeric materials is very
                                    high, the thickness of the material needs to be taken
                                    into account. Darcy's law, expressed by the equation
                                    q =  kiA, is used to calculate rate of flow, with
                                    transmissivity equal  to kt and i  equal  to the
                                    hydraulic gradient (see Figure 4-2):
                                    Figure 4-2.   Variables for calculating inplane flow  rates
                                               (transmissivity).
            q  = kiA  .       ; '             (5)

               = k(Ah/L) (w x t)|

            q/w = (kt) (Ah/L)   '

.   if       9   = kt

            q/w = 0(i)         I

   where   q/w = flow rate per unit width

            9   = transmissivity

Note that when i = 1.0, (q/w) =  9; otherwise it does
not.                           :

With a liquid flowing across ;the  plane of the
material, as in a  geotextile filter, the permeability
perpendicular to the plane can be divided by the
thickness, t, to obtain a new valu£, permittivity (see
Figure 4-3). In crossplane flow,  t is in the
denominator; for planar flow it is in the numerator.
Crossplane flow is expressed as:

           q  = kiA                         (6)

              = k(Ah/t)A

           q  = (k/t)AhA
           u; = (k/t) = (q/AhA)

   where   W  = permittivity
            q/A = flow rate per unit area ("flux")
                                                 56

-------
Thus, both transmissivity and permittivity values
allow for the thickness to be avoided in subsequent
analyses.
 Figure 4-3.  Variables for calculating crossplane flow rates
           (permittivity).

Table 4-1 shows some of the ASTM test methods and
standards for drainage and filter materials used in
primary leachate collection and leachate detection
and collection systems. Test methods are determined
by D18, the Soil and Rock Committee of ASTM, and
by D35, the Committee on Geosynthetics.

Primary Leachate Collection and
Removal (PLCR)  Systems
The  various design options for  primary leachate
collection systems are  granular  soil drains,
perforated pipe collectors, geonet drains, sand filters,
and  geotextile  filters. Figure 4-4 shows a cross
section of a primary leachate collection system with
a geonet drain on the side slope leading into a gravel
drain on the bottom. This gravel drain then leads
into a perforated pipe collector. A geotextile acts as a
filter protecting the geonet and sand acts as a filter
for the drainage gravel. Quite often  the sideslope
geotextile extends  over  the  bottom sand filter as
shown in Figure 4-4.

Granular Soil (Gravel) Drainage  Design
Current minimum  technology guidance  (MTG)
regulations require  that  granular soil drainage
materials must:

•  Be 30 centimeters (12 inches) thick.
•  Have 0.01 cm/sec  (= 0.02 ft/min) permeability
   (hydraulic conductivity).
•  Have a slope greater than 2 percent.
•  Include perforated pipe.
•  Include a layer of filter soil.
• Cover the bottom and side walls of the landfill.

There are two ways to calculate the required flow
rate, q, in granular soil drainage designs. One is
based on the above MTG values; the other is based on
the Mound Model (see Figure 4-5). Based on MTG
values:
                                                         q  = kiA

                                                           .= (0.02) (0.02) (1 x 1)

                                                            = 4x10-4 ft3/min
                                            (7)
                                                  Note that if MTG increases the required hydraulic
                                                  conductivity of the drainage soil to 1 cm/sec, the
                                                  above flow rate will be increased to 0.04 ft3/min.

                                                  In the Mound Model, the maximum height between
                                                  two perforated pipe underdrain systems is equal to:
h    =
 max
       L/C
   9
tan a
      tana   ,   o
+ 1 - 	V tan a + c
                                (8)
where c = q/k
k = permeability
q = inflow rate

The  two unknowns in the equation are  L,  the
distance  between pipes, and c, the amount of
leachate  coming through the system.  Using  a
maximum allowable head, hmax, of 1 foot,  the
equations are usually solved for L.

One method of determining the value of c is using the
Water Balance Method:
          PERC = P - R/0 - ST - AET
                                (9)
    where   PERC =
         percolation, i.e. the liquid
         that permeates  the solid
         waste (gal/acre/day).
            P     =  precipitation for which the
                     mean monthly .values  are
                     typically used.

            R/O   =  surface runoff.

            ST    =  soil moisture storage, i.e.,
                     moisture retained in the soil
                     after a given  amount of
                     accumulated potential water
                     loss or gain has occurred.

            AET  =  actual  evapotranspiration,
                     i.e., actual amount of water
                     loss during a given month.
                                                57

-------
Table 4-1,  Test Methods and Standards
ASTM Test Designation
(or other)
D2434
D2416
F405, F667
D4716
D4491
D4751
CW-022153
GRI-GTlb
Used to Determine
Permeability
Strength
General specification
Transmissivity
Permittivity
Apparent opening size
Gradient ratio
Long-term flow
Material
Soil
Underdrain pipe
HOPE pipe
Geonet, geocomposite
Geotextile
Geotextile
Geotextile
Geotextile
i
jValue Used for
1 PLCR, LDCR
PLCR, LDCR
PLCR, LDCR
PLCR, LDCR
1 PLCR filter
PLCR filter
' PLCR filter
PLCR filter
a U.S. Army Corps of Engineers Test Method.
bQeosynthetic Research Institute Test Method.
                                                                                            Perforated
                                                                                              Pipe
Figure 4-4.   Cross section of primary leachate collection systems.
                          Inflow
      I   1    i    i    1   1 •   1    1    i    1

   Drainage Layer      7^—	^ hn
Figure 4-5.   Flow rate calculations: Mound Model.
The range of percolation rates in the United States is
15 to 36 inches/year (1,100  to 2,700 gal/acre/day)
(U.S. EPA, 1988).               !

The computer  program Hydro;logic Evaluation
Landfill Performance Model (HELP) can also be used
to calculate c. HELP was developed to assist in
estimating the magnitude  o|f water-balance
components and the height of water-saturated soil
above the barrier layers. HELP [can be used  with
three types of layers:  vertical percolation, lateral
drainage,  and barrier  soil liner. By providing
climatological data  for 184  cities throughout the
United States, HELP allows  the user to incorporate
extended evaluation  periods without  having to
assemble large quantities of data (Schroeder et al,
1984).                          :
                                                 58

-------
Perforated Collector Pipe Design
The original perforated collector pipes in landfills
were made of concrete like those used in highway
underdrain systems. As landfills became higher, the
strength of such pipes became inadequate. Today,
perforated PVC pipes are commonly used, as  are
HDPE pipes.  New regulations require that all
materials be tested for chemical resistance as part of
the permit-approval process.

The three steps in designing perforated collector
pipes are:

1.  Obtain the required flow value using known
    percolation and pipe spacing.
2.  Obtain the required pipe size using the required
    flow and the maximum slope.

3.  Check the pipe strength and  obtain its ring
    deflection  to  determine tolerance against
    crushing.

Knowing the percolation and pipe spacing from the
previous  calculations, the required flow can be
obtained using the curve in Figure  4-6. The amount
of leachate  percolation at the particular site is
located on the x-axis. The required flow rate is  the
point at  which  this value intersects  with the pipe
spacing value determined from the Mound Model.
Using this value of flow rate and the bottom slope of
the site,  one can find the required  diameter for  the
pipe (see Figure 4-7). Finally, the graphs in Figures
4-8 and 4-9 show two ways to determine  whether or
not the strength of the  pipe is adequate for the
landfill design.  In Figure 4-8,  the vertical soil
pressure is located on the y-axis. The density of the
backfill  material  around  the pipe is used to
determine ring deflection.  Plastic pipe is not
governed by strength, so it will deform under
pressure rather than break. Twenty percent is often
used as the limiting deflection value for plastic pipe.
Using Figure 4-9 the applied pressure on the pipe is
located and traced to the trench geometry, and then
the pipe deflection value is checked for its adequacy.

Geonet Drainage Design
Table 4-2 presents a compilation of  currently
available geonets. The  structure and properties of
each are also identified. Geonets used in drainage
design must be chemically resistant to the leachate,
support the  entire weight of the  landfill, and be
evaluated by the ASTM test  D4716 as to allowable
flow rate or transmissivity.  This allowable value
must then be compared to the required value in the
design-by-function equation presented earlier.

In the D4716 flow test, the proposed collector cross
section should be modeled as closely as possible. The
candidate geonet usually  will be sandwiched
 C
 'e
    120
 2
 _o
 13
 pi
 c
100
    80
 P  60
 o  40-
 fc
 Q.
 I
 DC
    20-
         1      2      3     4.5
           Percolation, in inches per month
"Where b = width of area contributing to leachate collection pipe

Figure 4-6.  Required capacity of leachate collection  pipe
           (after U.S. EPA, 1983).

between a FML beneath and a geotextile above. Soil,
perhaps simulating the waste, is placed above  the
geotextile and the load platen from the test device is
placed above the  soil. Applied normal stress is
transmitted through the entire system. Then planar
flow, at a constant hydraulic  head, is initiated and
the flow rate through the geonet is measured.

Figure 4-10 shows the flow rate "signatures" of a
geonet between two FMLs  (upper curves) and  the
same geonet with the cross  section  described
abovedower curves). The differences between the two
sets of curves  represent  intrusion of the
geotextile/clay  into the apertures of the geonet.
Irrespective of the comparison in behavior, the
curves are necessary in obtaining an allowable flow
rate for the particular geonet being designed.

The required flow  rate can be calculated by three
different methods: (1) directly  from  minimum
technology guidance, (2) using an  equation
developed in the design manual, or (3) on the basis of
surface water inflow rate. To be conservative,  all
three calculations should  be  performed  and the
worst-case situation (e.g., that with the highest flow
rate) used for the required flow rate. The various
equations to determine the required flow rate or
transmissivity appear below:

1.  Geonet must be equivalent to MTG regulations
   for natural materials:
                                                59

-------
G.P.M. C.F.S.
                                                                                   Pipe Flowing Full
                                                                          Based on Manning's Equation n = 0.010
       '0.1 '     0.2   0.3   0.4 0.50.6  0.8 1.0        2.0    3.0  4.0 5.06.0 8.0  10
                                       Slope of Pipe in Feet per Thousand Feet
Figure 4-7.   Sizing of leachate collection pipe (U.S. EPA, 1983).
             9 S: 0.02 ft3/min-ft
                                (10)
 2.  Based on estimated leachate inflow (Richardson
     and Wyant, 1987):
Q    _
 reqd
                             2L sina
                                              (11)
 3.  Based on surface water inflow (U.S. EPA, 1986):

                  Q = CIA                    (12)

     where   Q= surface water inflow
             C= runoff coefficient
             I = average runoff intensity
             A= surface area

 Generally geonets result in high factors of safety or
 design ratios, unless creep becomes a problem or if
 adjacent materials intrude into the apertures.

 Granular Soil (Sand) Filter Design
 There are three parts to an analysis of a sand filter to
 be placed above drainage gravel.  The first
 determines whether or not the filter allows adequate
flow of liquids through it. The second evaluates
whether the void spaces are small enough to prevent
solids being lost from the upstream materials. The
third part estimates the long-term clogging behavior
of the filter.                    !

Required in the design of granular soil (sand) filter
materials  is the particle-size distribution of the
drainage system and the particle-size distribution of
the invading (or upstream) soils. The filter material
should  have its large and small size  particles
intermediate between the two extremes (see Figure
4-11). Adequate flow and adequate retention are the
two  focused design factors, but perhaps the most
important  is clogging. The equations for adequate
flow and adequate retention are:

«  Adequate Flow: d85f>(3 to 5) di5ds         (13)

•  Adequate Retention: disf < (3 to 5) dg5wf     (14)

There is no quantitative method to assess soil filter
clogging, although empirical guidelines are found in
geotechnical engineering references.

Geotextile Filter Design    :
Geotextile filter design parallels sand filter design
with some modifications. The three elements  of
                                                   60

-------
                  I
                 Q.

                 '5
                 15
                 o
                  II
                 Q_
                         12,000
                         10,000
                         8,000
                         6,000
                         4,000
                         2,000
                                        95%
                                        Soil
                                       Density
                                               Initial Effect of
                                               Ring Stiffness
                                                                             85%
                                                                              Soil
                                                                            Density
                                                                    75% Soil Density
                                                                     Plot of Vertical
                                                                      Soil Strain 6
                              0       5       10      15      20       25

                                  Ring Deflection, AY/D (%)  =  € Except as Noted


Figure 4-8.   Vertical ring deflection versus vertical soil pressure  for 18-inch corrugated polyethylene pipe in high pressure soil
           cell.
adequate  flow, soil  retention,  and clogging
prevention remain the same.

Adequate  flow  is  assessed by comparing the
allowable permittivity  with  the  required
permittivity. Allowable permittivity uses the ASTM
D4491 test method, which is well established. The
required permittivity utilizes an adapted form of
Darcy's law. The resulting  comparison yields a
design ratio, or factor of safety, that is the focus of
the design.
where
                                             (15)
               = permittivity from ASTM Test
                 D4491
          ' reqd
                                                                 — = inflow rate per unit area
                                                                 A.

                                                                hmax  =12 inches

                                                     The second part  of the geotextile filter design is
                                                     determining the opening size necessary for retaining
                                                     the upstream soil or particulates in the leachate. It is
                                                     well established that the 95% opening size is related
                                                     to the particles to be retained in the following type of
                                                     relationship
                                                                   095 < fct. (d50, CU, DR)
                                             (16)
where  Ogs = 95% opening size of geotextile (U.S.
              Army Corps of Engineers CW 02215
              test method)
        dso = 50% size of upstream particles
        CU = uniformity of the upstream particle
              sizes
                                                  61

-------
   10






O




LJrgiU




>****



-aSS^!
^"


^
^^







/
^^
	 	






XI
^^



3/D - 1.
3
B/D = 1.5

^- B/D = 1 .8
- -^"Vertical So\\ £
for Native So
757<
..-B/D
5 10 15 20 2
> Density
= o 	 1
5 3
train e
l@
0
              Ring Deflection, A Y/D (%)

Figure 4-9.   The effect of trench geometry and pipe sizing
           on ring  deflection (after Advanced  Draining
           Systems, Inc., 1988)
        DR = relative density of the  upstream
             particles

Geotextile literature documents the relationship
further.

The Ogs size of a geotextile in the equation is the
opening size at which 5 percent of a given size glass
bead passes  through the fabric. This value must be
less  than the  particle-size characteristics of the
invading materials. In the test for the Ogg size of the
geotextile, a sieve with a very coarse mesh in the
bottom is used as a support. The geotextile is placed
on top of the mesh and is bonded to the inside so that
the glass beads used in the test cannot escape around
the edges of the geotextile. This particular test
determines the Ogs value.  To  verify the factor  of
safety for particle  retention in the geotextile filter,
the particle-size  distribution of retained soil  is
compared to the allowable value using any of a
number of existing formulae.

The third consideration in geotextile design is long-
term clogging. The test method that probably will be
adopted by ASTM is called the Gradient Ratio Test.
It was originally formulated by the U.S. Army Corps
of Engineers and is listed in CW 02215. In the test,
the hydraulic gradient of 1 inch of soil plus the
underlying geotextile is compared with the hydraulic
gradient of  2 inches of soil. If the gradient ratio is
less than  3, the geotextile probably will not clog. If
the gradient ratio is greater than 3, the geotextile
probably will clog. An alternate to this procedure is a
long-term column flow test that also is performed in
a laboratory. The  test models a  given soil-to-fabric
system at the anticipated hydraulic  gradient. The
flow rate through the system is monitored. A long-
term flow rate at a constant value indicates an
equilibrium between the  soil and the geotextile
system.  If clogging occurs, the flow  rate  will
gradually decrease until it stops altogether.


Leachate Removal Systems
Figure 4-12 shows a low volume sump in which the
distance from the upper  portion of the concrete
footing to the lower portion is approximately 1 foot.
One foot is an important  design number because
EPA regulations specify a maximum leachate head
of 1 foot. Low volume submersible sumps present
operational problems, however.  Since they run dry
most of the time, there is a likelihood  of their
burning out. For this reason, landfall operators prefer
to have sumps with depths between 3 and 5 feet
instead of 1 (Figure 4-13),  even though the leachate
level in a high volume sump will be greater than the
1-foot maximum.

The leachate removal standpipe must be extended
through the entire landfill from liner to cover and
then through the cover  itself.  It also must be
maintained for the entire post-closure care period of
30 years or longer.

Leak  Detection, Collection, and  Removal
(LDCR) Systems

The leak detection, collection, and removal system
(LDCR) is  located between the primary  and
secondary liners in landfills, surface impoundments,
and waste piles. It can consist of either granular soils
(i.e., gravels) or geonets.

Granular Soil (Gravel) Drainage Design
As with the primary  leachate  collection system
above  the liner, leak  detection  systems between
liners  are designed by comparing allowable flow
rates with required flow rates. The allowable flow is
evaluated as discussed in the section on granular soil
(gravel) drainage design for PLCR systems. The
required flow is more difficult to estimate. This value
might be as low as 1 gal/acre/day or many times that
amount. It is site specific and usually  is a rough
estimate. Past designs have used 100 gal/acre/day for
the required flow rate. Data from; field monitoring of
response action plans (RAPs) will! eventually furnish
more realistic values. A pipe network for leachate
removal is required when using granular soils.

 Geonet Drainage Design
For a geonet LDCR system,  the flow rate for the
 geonet is determined in the laboratory from ASTM
 D4716 test method, and the value is modified to meet
 site-specific situations. The geonet flow rate design
                                                62

-------
Table 4-2.  Types and Physical Properties of Geonets (all are polyethylene)
                                              Roll Size, width/length
                               Thickness
Approx. Apperture Size
 Manufacturer/Agent    Product Name
Structure
                                               -- ft.
                              mils
                                                                         mm
                                                                                   in.
                                                                                             mm
Carthage Mills


Conwed Plastics




Fluid Systems Inc.
• Tex-Net (TN)


• Poly-Net (PN)





Geo-synthetics



Gundle

Low Brothers


Tenax



Tensar


FX-2000 Geo-Net
FX-2500 Geo-Net
FX-3000 Geo-Net
XB8110
XB8210
XB8310
XB8410
XB8315CN
TN-1001
TN-3001
TN-4001
TN-3001 CN
PN-1000

PN-2000
PN-3000
PN-4000

GSI Net 100

GSI Net 200
GSI Net 300
'Gundnet XL-1
Gundnet XL-3
Lotrak 8
Lotrak 30
Lotrak 70
CE1
CE2
CE3
CE600
DN1-NS1100
DN3-NS1300
-NS1400
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
foamed, and
extruded ribs
extruded ribs
extruded ribs
foamed, and
extruded ribs
foamed, and
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded mesh
extruded mesh
extruded mesh
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
extruded ribs
7.5/300
7.5/300
7.5/220
6.9/300
6.9/300
6.9/300
6.9/220
6.9/300
7.5/300
7.5/300
7.5/300
7.5/300
6.75/300

6.75/300
6.75/300
6.75/300

..

—
- •
6.2/100
6.2/100
6.6/164
6.6/164
6.6/164
4.8/66
7.4/82
7.4/82
5.5/100
5.2/98
6.2/98
6.2/98
2.3/91
2.3/91
2.3/67
2.1/91
2.1/91
2.1/91
2.1/67
2.1/91
2.3/91
2.3/91
2.3/91
2.3/91
2.0/91

2.0/91
2.0/91
2.0/91

„

—
-
1.9/30
1.9/30
2.0/50
2.0/50
2.0/50
1.5/20
3.8/25
2.2/25
1.67/30.5
1.6/30
1 .9/30
1 .9/30
200
250
300
250
160
200
300
200
250
200
300
200
250

160-
200
300

250

160
200
250
200
120
200
290.
250
200
160
160
220
150
200
5.1
6.3
7.6
6.3
4.1
5.1
7.6
5.1
6.3
5.1
7.6
5.1
6.3

4.1
5.1
7.6

6.3

4.1
5.1
6.3
5.1
3.0
5.2
7.3
6.3
5.1
4.1
4.1
5.6
3.8
5.1



0.3 x 0.3
0.35 x 0.35
0.3 x 0.4
0.25 x 0.25
0.3 x 0.3




0.3 x 0.3

0.3 x 0.4
0.35 x 0.35
0.25 x 0.25





0.3 x 0.3
0.3 x 0.3
0.3 x 0.3
1.2x1.2
2.8 x 2.8
0.3 x 0.25
0.3 x 0.35
0.3 x 0.25
0.3 X 0.25
0.3 x 0.3
0.3 x 0.3
0.3 x 0.3



8x8
9x9
8x10
6x6
8x8




8x8

9x9
8x10
6x6





8x8
8x8
8x9
30x27
70 x70
8x6
9x9
8x6
8x6
8x8
8x8
8x8
ratio is then determined in the same way as for the
granular system. No pipe network is needed.

A concern when using geonets with a composite
primary liner  design is  the effect of geotextile
intrusion and creep on the allowable flow rate (see
Figure 4-14). In composite primary liner systems, the
geonet is placed immediately below a clay liner with
a geotextile as an intermediate barrier. The design of
this geotextile is important because clay  particles
can go through large voids in an open  woven
geotextile, necessitating the use of a needle-punched
nonwoven geotextile of at least 8 to 10 ounces per
square yard (oz/yd2) mass per unit area. Even with
this precaution, the laboratory test to evaluate the
allowable flow rate should simulate the anticipated
cross section in every detail.

Response Time
EPA specifies that the minimum detection time  for
leachate entering the leak detection  system of a
                LDCR system is less than 24 hours. Response time
                calculations  are based on velocity in the geonet
                and/or granular soil drainage layer. Darcy's law is
                used to calculate flow velocity in the geonet,  and a
                "true" velocity must be used for granular soil.

                Figure 4-15 shows the response time calculation for a
                leachate leak through a primary liner traveling  40
                feet through the geonet on the side wall and 20 feet
                through the  sand at the bottom.  The  resulting
                response times  are 1.5 hours in the geonet and 6.2
                hours in the soil; giving a total response time of 7.7
                hours.

                The travel time  in a geonet is very short; so a 24-hour
                response time can easily be achieved. With granular
                soils, the travel  time will be much longer.

                Leak Detection Removal Systems
                Leak detection removal systems require monitoring,
                sampling,  and leachate removal. Any leachate that
                                                 63

-------
                it:
                c

                I
                42


                C
                CC
                                          5,000         10,000         15,000



                                                Normal Stress (Ibs/sq. ft)


                                          (a) FML - Geonet - FML Composite
20,000
                                          5,000         10,000         15,000



                                                 Normal Stress (Ibs/sq. ft)


                                     (b) FML - Geonet - Geotextile - Clay Soil Composite




Figure 4-10. Flow rate curves for geonets in different composite situations.
20,000
                                                            64

-------
    100
       Gravel    Sand       Silt

                 Particle Size (log)
Clay
  Figure 4-11.  Design based on particle-sized curves.
 penetrates the primary liner system and enters the
 secondary system  must  be removed. During
 construction the LDCR system  may accept runoff
 water, but once the landfill is in operation it only
 removes any  leakage coming through the primary
 liner. The most common removal system consists of a
 relatively large diameter-pipe running down the side
 wall between the primary and secondary liners to the
 low point (sump)  in the LDCR. The  pipe  must
 penetrate the primary liner at the top. A submersible
 pump is lowered through the pipe periodically for
 "questioning" of the quantity of fluid coming into the
 system (see Figure 4-16).  The choice of monitoring
and retrieval  pump depends on  the  quantity of
leachate being removed.

An alternate system, one based on gravity, requires
penetration of both the FML and clay components of
the secondary composite liner system as shown in
Figure 4-17.  It also requires a  monitoring and
collection manhole on the opposite side of the landfill
cell (see Figure 4-18). The manhole and connecting
pipe, however, become an underground storage tank
that needs its own secondary containment and leak
detection systems.
                Surface Water Collection and Removal
                (SWCR) Systems
                The third part of liquids management is the surface
                water collection and removal system (SWCR); It is
                placed on top of the completed facility and above the
                cover FML. The rainwater  and snowmelt that
                percolate through the top soil  and vegetative cover
                must be removed to a proper upper drainage system.
                Figure 4-19 illustrates the major components of a
                surface water collector system. The design quantity
                for the amount of fluid draining into the surface
                water collector system can be determined by either a
                water balance  method or  the computer program
                HELP discussed previously (see Figure 4-20).
                  Steel Plate
                                             36" -48" RCP
                                                    •*—#-
                                             Concrete Base
                                                                 Gravel
                                                                                    >»LCR
                   ***•••••••£•«•••••••••••••••••••••••••••••••••••


                    FML-T
                                                                            MW^^

Figure 4-12. Leachate removal system with a low volume sump.
                                                65

-------
-Standpipe
- Air Space
Figure 4-13.  Leachate removal system with a high volume
           sump.
          J    I   I   i  *.*.>. *.^P-™L
                          •FML ''vuii'Possible Intrusion
^
        '." *;' Clay Beneath Secondary FML- -'/'_ -.
                                       -S-FML
Figure 4-14.  Geotextile used as barrier material to prevent
           extrusion of upper clay into geonet drain.
Surface water drainage systems can be composed of
granular soils, geonets, or geocomposites, but the
majority of drainage systems use granular soil. This
is particularly true in frost regions where it  is
necessary to have 3 to 6 feet of soil above the FML to
satisfy the requirements for frost penetration.  In
such cases, 1 foot of granular soil thickness can serve
as the surface water collector. If good  drainage
materials are not available, if the site  is too
extensive, or if natural materials would add
undesired thickness, a geonet or geocomposite can be
used. The advantage of drainage  geocomposites is
their higher flow rate capabilities over geonets  or
granular soils. Table 4-3 lists a number  of
geocomposites that can be used for drainage systems.
All of these systems have polymer cores protected by
a geotextile filter. Although many of the polymers
cannot withstand aggressive leachates, this is not an
issue in a surface drainage collector where the only
contact is with water. The crush strengths of the
geocomposites are generally  lower than for geonets,
but that too  is not a problem in  a surface water
collector. The heaviest load the geocomposite would
be required to  support  probably would  be
construction equipment used to place the cover soil
and vegetation on the closed facility.
                                                   The design for the surface water collector system is
                                                   determined by an allowable flow rate divided by a
                                                   required flow rate. Allowable rates for geocomposites
                                                   are determined experimentally by iexactly the same
                                                   method as for geonets.  Figure 4-21 shows the flow
                                                   rate behavior for selected drainage geocomposites.
                                                   The specific cross section used in the test procedure
                                                   should replicate the intended design as closely as
                                                   possible. For the required flow rate, Darcy's law or
                                                   HELP can  be used.  Then the design-by-function
                                                   concept is used to determine the design ratio (DR), or
                                                   factor of safety (FS).
                                                            DR = FS =
                                                   allowable flow rate
                                                    required flow rate
                               Gas Collector and Removal Systems
                               Degradation of solid waste materials in a landfill
                               proceeds from aerobic to anaerobic  decomposition
                               very quickly, thereby generating gases that collect
                               beneath the closure FML. Almost 98 percent of 'the
                               gas produced is either carbon dioxide (CC>2) or
                               methane (CH4).  Because COa is heavier than air, it
                               will move downward and  be removed with the
                               leachate. However, CH4, representing about 50
                               percent of the  generated gas, is  lighter than air
                               and.therefore, will move upward and collect at the
                               bottom of the facility's "impermeable" FML. If the
                               gas is not removed,  it will produce a buildup  of
                               pressure on the FML from beneath.

                               In gas collector systems, either a granular soil layer
                               or a needle-punched nonwoven geotextile is placed
                               directly beneath the FML or clay of a composite cap
                               system. Gas compatibility and air transmissivity are
                               the design factors that must be considered. Methane,
                               the most predominant gas,  should  be compatible
                               with most types of geotextiles including polyester,
                               polypropylene, and polyethylene.

                               The thickness  design should  be  based on gas
                               transmissivity tests. Since water has a viscosity of
                               1,000 to 10,000  times that of gas, qaiiow for gas flow
                               should compare very favorably with  the results of a
                               water transmissivity test. As an example, Figure 4-
                               22 shows air transmissivity versus normal stress for
                               a 12 oz/yd2  needle-punched nonwoven geotextile.
                               Alternatively, one could  look directly  at
                               permeability coefficients where geotextile air flow is
                               several orders of magnititude greater than the MTG-
                               required values as shown in Figure 4-23. In the test
                               method, the geotextile specimen fits underneath a
                               load bonnet. Then the load, equivalent to the cover
                               soil, is added and gas is brought to the inside of the
                               geotextile. The gas flows through the geotextile and
                               into a shroud that goes on the outside of the flanges
                               and registers on an air meter. The resulting applied
                                                66

-------
            Example:
           vTe 'Taut.'
                         -  .CO I  M/
                                                      ftCc.
                                                        f  ao
                                     • "
                                                                        0.3
Figure 4-15.  Example problem for calculation of primary liner leak response time.
stresses, gas pressures, and gas permeabilities  are
then recorded, and, if necessary, converted into  gas
transmissivity. The allowable gas transmissivity is
then divided by the required gas transmissivity to
yield the design ratio, or factor of safety.
Gas generation occurs over a period of 70 to 90 years,
so gas collector and removal systems must work for
                                  at least that  long to avoid  gas pressure on the
                                  underside of the cover.

                                  Gas generation might  also cause problems in
                                  "piggyback" landfills, landfills that have been built
                                  on  top  of one another. It is still  unknown what
                                  happens to gas generated in an old landfill after a
                                  hew liner is  placed on top of it. To  minimize
                                  problems, the old landfill should have a uniform

                                                67

-------
                                                                                       Leakage
                                                                                       Removal
                                                                                                Requires
                                                                                               Penetration
                                                                                                of P-FML
                                         Submersible Pump
                                            within Pipe
Figure 4-16.  Secondary leak detection removal system via pumping between liners and penetration of pimary liner.
                                                                             A  . _    _  „             Penetration
                                                                             Anti-Seep Collars           Of S-F
                                                                                                   ;    and Clay


Figure 4-17.  Secondary leak detection removal system via gravity monitoring via penetration of secondary liner.
                                                         68

-------
                 Finish Grade to Slope  .
                  Away from Manhole  xj:-. :• •
           Discharge Line from Leak
         Collection/Detection System
        (Solid Wall-6" Dia or Larger)
                                                                                                  Manhole Frame and Cover
                                                                                                       with Vented Lid
                                                                                                  Granular Backfill
                                                                                             _;>• 4' LD Manhole
                                                                                                  Point of Continuous or
                                                                                                  Intermittent Monitoring
    Note: Manhole will be equipped with discharge line to
          leachate removal system or with discharge pump
Figure 4-18.  Monitoring and collection manhole (E. C. Jordan, 1984).
         Vegetative
            Layer
         Drainage
           Layer
      Low Permeability
          Layer

FMI
(> 20 mils in
thickness)

Compacted
Soil Layer
a 12'
, J.

> 24
1
                                                                                                         Functions
  Vegetation'or Other
Erosion Control Material
 at and Above Surface

 Top Soil for Root
     Growth
 Remove Infiltrating
       Water
 Increases Efficiency
of Drainage Layer and
 Minimizes Infiltration
      into Unit
Figure 4-19.  Surface Water Collection and Removal (SWCR) system.
                                                             69

-------
                       Computer Code "Help" will give design (required) flow rate
                                                                          Leachate Collection Pipe
                                                                          To Leachate Collection Sump
Figure 4-20. Design methodology to estimate cover soil infiltration to SWCR system.
slope and possibly an accordian-pleated bottom cross
section.  Then  the gas could escape  from  the
underside and be collected from the high gradient
side of the site.

As seen in Figure 4-24, the details of a gas collection
system are quite intricate and yet very important to
the proper functioning of the system.

References
1. Advanced Drainage Systems, Inc. 1988. Report.
2.
3.
    Columbus,
    Inc.
           OH: Advanced Drainage Systems,
Richardson,  G.N.  and D.W.  Wyant. 1987.
Construction criteria for geotextiles. Geotextile
Testing and the Design Engineer. ASTM  STP
952.

Schroeder, P.R., A.C. Gibson and M.D.  Smolen.
1984. The Hydrologic Evaluation of Landfill
Performance   (HELP)  Model:   Vol.   II,
                                                  Documentation for Version I. EPA/530/SW-
                                                  84/010.  Cincinnati,  OH: EPA Municipal
                                                  Environmental Research Laboratory.

                                                  U.S. EPA. 1983. U.S. Environmental Protection
                                                  Agency.  Lining of waste impoundment and
                                                  disposal  facilities. SW-869. Washington, DC:
                                                  Office of Solid Waste and Emergency Response.
                                                70

-------




























(A

CO
1
2
Q
2
'35
o
U>
E
L vailable Geocc
«i
1
i
o
o

able 4-3.
i-
'co
J-^

"S ^~
'§ ^
"cl! ®
S
ffi
CO 'co
CC Q.
g in
LL '-
©

1
CO .C"

CO

CO
CO
l.f
o £
H

~—s
.§1
cos
=5S
cc i

.32
1
O

CL
§
O
§
1
CO
03
O
O



CD
c*
Product Nan

+*
03
I
£
2

•*=
i


CO







00




CO
co



in
r-»


o


CD
C
03
Polypropyll

g
1

S
o
o
•a
03
a.
Q.


co
S
Amerdrain 480

S-
8
c
'co
Q
*£.
O
>
American V



itii






: ; : i





! ! ! !



oooo
°.§°§


ii^«



Polyester
Polyester

co co co co
c c cz c
o o o o
>< Ss >> ;*
-z.-z.-z-z

03 03 03 O
8888
c c c c
03 CD 03 03
Q. Q. Q. Q.
oooo




Enkamat 7010
Enkamat 7020
Enkamat 9010
Enkamat 9 120





(-,
o
O
LU
CO
ffl

r- CO

CM C33 !






CO 9 CM




Q) IO '
CO CO Is-



in in in
in co t-~
CM r-~ in


3.0/450
3.6/125
3.5/80


ggg
Polypropyll
Polypropyl
Polypropyl

iyethylene
iyethylene
iyethylene
ooo
CL CL CL
03 fl) 03
111
CO CO CO
333
OOO




O 0
ooo
CO CM •*
S S S
XXX



CO
.g

3
•o
C
CO
3
m


00 c\J







05 oj



in

CO ^



§0
o
CO O


o 9


g
Polyprople

03
C
03
1
f
CD
CJ 	
03 S
•£2 CO
CO Q-
& CO
3 CL
O LU




Tiger Drain
Geotech Drain
Board



CO
03


CO
£5 CD
LU O

co co
i .x • iii co
i in r- III CO






j ?• co in m m {5




•* in o in
! O CM CO £31
r- t—



SO O OOO O
. in in co co in o
CM CM CM m m f» o


o o O
oo in in o 2
§ 88"§ §
T-

03 CD 03 03 03 03
tc c e c e
03 03 03 CD CD
•> "5, "5. "5. "5,
Ct CL CL CL Q.
2 2 2 2 S 2
a. a. CL Q. Q. a.
CL Q. Q. D. CL CL CL

JQ3 03 03
C C 03 03 CD C
•^ CD 03 C C C CD
S ••>.•>. £ £ E •>.
2 £ S S'S'S' S
Q. CD 03 W CO 03 03
CX. • ^ ^ Q. Q. Q. Q_

5 .g .Q .g .g
11 II 1 ;§3
LU LU LU LU LU CC


03
S
1 8.8 S 2
I 88 Iff °
i c c c5 co co 5
5 11 in I
X -^ 2S5 x



1' S
-£ CO
C ' "C
>i CL
"' 03 O
|c 1 |
X -5 2 2.



1 *






in r-
ro •*
CM CM


co ^

"S



Sfe
tO h*


1.6/49,98
3.6/98


m S
Polypropyl
Polypropyl

Iyethylene
Iyethylene
o o
CL CL






.

i
Q
2
CL



^*






S •*





1 '



o o
CO <*
CM CM


5.3/100
5.3/100


03 03
"o 'o
CL CL

g g
0 03
>, >>
CL £

Extruded rib
Extruded rib




88
r- CM
00
Q Q






1

|

'S
i
e
E
2

>s
g •
^
c
03
£
_
1
I
CO
CD
3
§
03
.C
H
.-S"
11
2 ra
"CO" O
oT"^
is numerica
nd concepts
«± CO
i!
c •—
9|
Bw
03
^_ «
aulic gradiem
1, manner of f
•n
>,^

CO g
03 03
^3 "^
11
P (0
I'l
C§ 03
s«
2-S
^ *CO
*- c
> O
S §
= CD
0 |
-C
The values
literature w
*

-------
                                                               15
   100
    10
o>

I
CE
    1.0
 Q
    0.1
                               Normal Pressure Ib/in2/lb/ft2
                                           .-0/0
                                             5/720
                                             10/1440
                                             15/2160
                                             20/2880  •
                       \\_

                                                               10
       0.01
                     0.10              1.0
                        Hydraulic Gradient

                              (a)
                                                        10.0
                                                                     700
                                                                      600
                                                                      500
                                                                      400
                                                                   •i 300
                                                                      200
                                                                      100
                                                                     OOOL
                                                                          0.0   0.1
                                                                          U-L.
 0.2   0.3   0.4   0^5   0.6
     Thickness of Ma|t, d(in)
	i	i	
                                                                                                                0.7
                                                                          0 ' 25            50            75
                                                                                        Residual Thickness, n(%)
                                                                                                 (b)
                                  100
Figure 4-21.  Flow rate behavior of selected geocomposite drainage systems.
             (a) Mirardrain 6000 at hydraulic gradients of 0.01 to 1.0
             (b) Enkadrain at hydraulic gradient of 1.0
                                                            72

-------
       4.0
   £•  3.0
       1.0
                                          Ua = 3.5 psi
                                          Ua = 1.0 psi
                                         Ua =  0.1 psi
                  j	I
        0        500     1000    1500    2000    2500
                             Stress (psf)


Figure 4-22.  Air transmissitivity versus applied normal stress
             for one layer of Fibretex 600R.
                                                                      250
                                                                      200
                                                                  I   150
                                                                  CD

                                                                  CD   100
                                                                       50
                                                                                                         Ua = 3.5 psi
                                                                                                         Ua = 0.1 psi
                                           J	I
         0        500     1000    1500    2000    2500

                               Stress (psf)


Figure 4-23.  Inplane  coefficient of air permeability versus
             applied  normal stress for one  layer of Fibretex
             600R.
                                                           73

-------
                      Steel Clamp .
                      WELDS
                                             . Mastic
                                            *»«»»«»«^« JJ» M
                                            .«»*•... •*/£&•
                                Boot Seal at FMC
                         Gasket
                            ^
                              Flange Seal at FMC
                                                              Vent to Atmosphere  /^_?
                                                                          •4	¥*•
                                                                          Riser
                                                Cover Soil
                                                                                                             • Filter
                                                                                             :  SWCR '•••'•'•.- .'
                                                                                                              FMC
                                           j>   Compacted Soil

                                           \           ;
                                                                                         i
                                                                      :.  Perforated Pipe  '.- . '.;. •_ o'as Vent .
                                                                              Operational Cover
               - Liner
                      Air/Gas Vent
Place Vent Higher than Maximum Liquid Level
at Over-Flow Conditions

 Two-Inch Minimum
                           •^^^fesP^—
                . Geotextile or "^SsS^J?—Gas Flow
                 Drainage Composite
                        Openings in Vent to be Higher than
                        Top of Berm or Overflow Liquid Level


                                          Air/Gas Vent Assembly
                                             —Approx. Six Inches
             ~Geotextile or^srsf
              Drainage Composite
                                                                        Wind Cowl Detail I/'     —
                                                                                      r   —
                                                                                                          Geomembrane
                                                      Concrete
                                                    Bond Skirt of Vent to Liner
                                                *•?— Gas Flow


Figure 4-24. Miscellaneous details of a gas collector system.
                                                           74

-------
                      5.  SECURING A COMPLETED LANDFILL
Introduction
This chapter describes the elements in a closure or
cap system of a completed landfill, including flexible
membrane caps, surface water collection  and
removal systems, gas control layers, biotic barriers,
and vegetative top  covers.  It  also discusses
infiltration, erosion control, and long-term aesthetic
concerns associated with securing a completed
landfill.

Figure 5-1 shows a typical landfill profile designed to
meet EPA's proposed minimum technology guidance
(MTG) requirements. The upper subprofile comprises
the cap, or cover, and includes the required 2-foot
vegetative top cover, 1-foot lateral drainage layer,
and low permeability cap of barrier soil (clay), which
must be  more than 2 feet thick. This three-tier
system also includes an optional flexible membrane
cap and an optional  gas control layer. The guidance
originally required a 20-mil thick flexible membrane
cap, but EPA currently is proposing  a  40 mil
minimum.

Flexible Membrane Caps
Flexible membrane caps (FMCs) are placed over the
low permeable clay cap and beneath  the  surface
water collection and removal (SWCR) system. FMCs
function primarily in keeping surface water off the
landfill and increasing the efficiency of the drainage
layer.  EPA leaves  operators with the  option of
choosing  the synthetic material  for the FMC  that
will be most effective for site-specific conditions. In
selecting materials, operators should keep in mind
several distinctions between flexible membrane
liners  (FMLs) and FMCs. Unlike a FML,  a FMC
usually is not exposed to leachate,  so  chemical
compatibility is not an issue. Membrane caps  also
have low normal  stresses acting on them in
comparison with FMLs, which generally  carry the
weight of the landfill. An advantage FMCs have over
liners is that they are much easier to repair, because
their proximity to the  surface of the facility makes
them more accessible. FMCs  will, however, be
subject to greater strains  than FMLs due  to
settlement of the waste.

Surface Water Collection and Removal
(SWCR) Systems
The SWCR system is built on top of the flexible
membrane cap. The purpose of the SWCR system is
to prevent infiltration of surface water  into the
landfill by containing and systematically removing
any liquid that collects  within it. Actual design
levels of surface water infiltration into the drainage
layer  can be calculated  using the water balance
equation  or the Hydrologic Evaluation of  Landfill
Performance  (HELP) model. (A more  detailed
discussion of HELP is contained in Chapter Four.)
Figure 5-2 shows  the results of two verification
studies of the HELP model published by EPA.

Errors in grading the perimeter of the cap often
integrates (or cross-connects) the SWCR system with
the secondary  leak detection and removal system,
resulting in  a significant amount of water
infiltrating the secondary detection  system. This
situation should be remedied as soon as possible if it
occurs. Infiltration of surface  water is a particular
concern in nuclear and hazardous waste facilities,
where gas vent stacks are found. A containment
system should be  designed to prevent water from
entering the system through these vents.

In designing a SWCR system above  a FMC, three
issues must be considered: (1) cover stability, (2)
puncture  resistance, and (3) the ability of the closure
system to withstand considerable stresses due to the
impact of settlement. Figure 5-3 illustrates the
effects of these phenomena.

Cover Stability
The stability of the  FMC supporting the SWCR
system can be affected by the materials used  to
construct the drainage layer and by the slope of the
site. In some new facilities, the drainage layer is a
geonet placed on top of the flexible membrane cap,
                                               75

-------
                                  '•Primary Anchor Trench
I      I
I
                           Secondary Anchor Trench
                     Cap Anchor Trench
Figure 5-1. Typical geosynthetic cell profile.
with the coefficient of friction between those two
elements being as low as 8 to 10 degrees. Such low
friction could allow the cover to slide. One facility at
the Meadowlands in New Jersey is constructed on a
high mound having side slopes steeper than 2:1. In
order to ensure adhesion of the membrane to the side
slopes  of the facility, a nonwoven geotextile was
bonded to both sides of the FMC. Figures 5-4 and 5-5
give example  problems that evaluate  the sliding
stability of a SWCR system in terms of  shear
capacities and tensile stress.

Puncture Resistance
Flexible membrane caps must resist penetration by
construction equipment, rocks, roots, and other
natural phenomena.  Traffic by  operational
equipment can cause serious tearing. A geotextile
placed on top of or beneath a membrane increases its
puncture resistance by three or four times. Figure 5-
6 shows the results of puncture tests on several
common geotextile/membrane combinations.
Remember, however, that a  geotextile placed
berieath the FMC and the clay layer will destroy the
composite action between the two. This will lead to
increased infiltration through penetrations in the
FMC.

Impact of Settlement
The impact of settlement is a major concern in the
design of the SWCR system. A number of facilities
have settled 6 feet in a single year, and 40 feet or
more over a period of years. The Meadowlands site in
New Jersey, for example, was built at a height of 95
feet, settled to 40 feet, and then was rebuilt to 135
feet. Uniform  settlement can actually be beneficial
                               by compressing the length of the; FMC and reducing
                               tensile strains. However, if waste does not settle
                               uniformly it can be caused  by interior berms  that
                               separate waste cells.

                               In one current closure site  in California, a waste
                               transfer  facility with an 18-foot wall is being built
                               within a 30-foot trench on  top of a 130-foot high
                               landfill. The waste transfer facility will settle faster
                               than the adjacent area, causing tension at the edge of
                               the trench. Electronic extensometers are proposed at
                               the tension points to  check  cracking strains in the
                               clay cap and FMC.

                               Settlements can be estimated, although the margin
                               for error is large. Secure  commercial hazardous
                               waste landfills have the smallest displacement, less
                               than 1.5 percent. Displacements at new larger solid
                               waste landfills can be estimated at 15 percent, while
                               older, unregulated facilities  with mixed wastes have
                               settlements of up to 50 percent. Figure 5-7 -gives an
                               example problem showing how to verify  the
                               durability of  a FMC under long-term settlement
                               compression.                  :
                                Gas Control Layer
                                Gas collector systems are installed directly beneath
                                the low permeability clay cap in a hazardous waste
                                landfill.  Landfills  dedicated to receiving  only
                                hazardous wastes are relatively  new and gas has
                                never been detected in these systems. It may take 40
                                years or more for gas to develop  in a closed secure
                                hazardous waste landfill facility.  Because the  long-
                                term effects of gas generation are not known, and
                                                76

-------
                           , i*. 5^ JL
Placing FMC at edge of cap.
 costs are minimal, EPA strongly recommends the
 use of gas collector systems.

 Figure 5-8 shows details from a gas vent pipe system.
 The two details at the left of the illustration show
 closeups of the boot seal and flange seals located
 directly at the interface of the SWCR system with
 the  flexible membrane cap.  To keep the vent
 operating properly, the slope of. the closure  system
 should never be less than 2 percent; 5 to 7 percent is
 preferable. A potential problem with gas collector
systems is that a gas venting pipe, if not properly
maintained, can allow surface water to drain directly
into the landfill waste.

Figure 5-9 illustrates two moisture control options in
gas collector systems. Gas  collector systems will
tolerate a large  amount of moisture  before air
transmissivity is affected. Figure 5-10 shows air and
water transmissivity in a needle-punched nonwoven
geotextile. Condensates from the gas collector layer
that  form beneath the clay and flexible membrane
                                                  77

-------
 OC

 I
 CO
 O
                 Legend
             i Help Simulation
             1 Field Measurement
                                                     • Cover Stability
 =  125-j

 0  100-
            Jan
            1973
        Jan
        1974
 Jan
 1975
Date
Jan
1976
Jan
1977
 Figure 5-2.
Cumulative comparison of HELP simulation and
field  measurements, University of Wisconsin,
Madison, uncovered cell.
cap also can be taken back into the waste, since most
hazardous wastes are deposited very dry.

Biotic Barriers
A biotic barrier is a gravel and rock layer designed to
prevent the intrusion of burrowing animals into the
landfill area. This protection is primarily necessary
around the cap but, in some cases,  may also be
needed at the bottom of the liner. Animals cannot
generally penetrate a FMC, but they can widen an
existing hole or tear the material where  it has
wrinkled.

Figure 5-11 shows the gravel filter and cobblestone
components of the biotic barrier and their placement
in  the landfill system. The proposed  1-meter
thickness for a biotic  barrier should effectively
prevent penetration by all but the smallest insects.
Note that the biotic barrier also serves as the surface
water collection/drainage layer. Biotic  barriers used
                                           Puncture Resistance
                                                                       Wheel
                                                       Impact of Settlement
                                                                    ^- Interior Berms   •

                                                     Figure 5-3.  SWCR systems considerations.
                                         in nuclear caps may be up to 14-feet thick with rocks
                                         several feet in diameter. These barriers are designed
                                         to prevent disruption of the landfill by humans both
                                         now and in the future.
                                         Vegetative Layer
                                         The top layer in the landfill profile is the vegetative
                                         layer. In the short term, this layer prevents wind and
                                         water erosion, minimizes the percolation of surface
                                         water into the  waste layer,  and  maximizes
                                         evapotranspiration, the loss of water from soil by
                                         evaporation and transpiration. Tfre vegetative layer
                                         also functions in the long term to enhance aesthetics
                                         and to promote a self-sustaining ecosystem on top of
                                         the landfill. The  latter  is of primary  importance
                                         because facilities may not be maintained for an
                                                  78

-------
Meadow/lands test of slip-resistant FMC.


 indefinite period of time by either government or
 industry.

 Erosion can seriously affect a landfill closure by
 disrupting the functioning of drainage layers and
 surface water and leachate collection and removal
 systems. Heavy erosion could lead to the exposure of
 the waste itself. For this reason, it is important to
 predict the amount of erosion that will occur at a site
 and reinforce the facility accordingly. The Universal
 Soil Loss Equation shown below can be used to
 determine soil loss from water erosion:

                   X = RKSLCP

     where X  = soil loss

            R  = rainfall erosion index

            K  = soil erodibility index
           S = slope gradient factor

           L = slope length factor

           C = crop management factor

           P = erosion control practice

Figure 5-12 can be used to find the soil-loss ratio due
to the slope of the site as used in the Universal Soil
Loss Equation. Loss from wind erosion  can be
determined by the following equation:

                 X' = I'K'C'L'V

    where  X' = annual wind erosion

           I' = field roughness factor

           K' = soil erodibility index
                                                  79

-------
Cell Component: 5 uRFAee WATER COUEC.-POM/ REMOVAL
Con^idontion' ^>HEAP FAILURE
£«VE A Soil. A^UO
Required Material Properties
* SW^R T* TMC. £L
Sni*,*. StfllU^tH °f ^^^^^^Aii^vj
frifl UIC UniTxn
EVALUATE ^LIOIU^ srAO
QCSiqu RATIO AqAiuir
Range
S^
Analysis Procedure:
+~s-
P"~ -t«jofi> ^ ' —
^O^AL'diM' SMSAA. SlBtis xaooe f O6i.»" 5
/ L~16'1
•TALV.U,
N ••*• SM,M
Design Ratio:
^^TIR 4i.ioiMq 0*^^ 2.O
ivocR SHIAR on> if.o
Test
U.PS U'PTH
5-rwEM
SrtEAC?
Standard
Z«
oPE af cToVER
W^R SY- (1184)
Example:
- SUJ<:PS -r» FMC .2.5*
•cT0vER -Son. DcprH - 4* ;
•SHEAR SJ-RC^TM SwcR= I5lt'/iu't j

i»u *.n .
^Zil2o~ 45° P^F
i5)^AL<:LjLATe PE^ICJM f?A.Tio r<»« "Su^R •SHEAR
l^> x 144

(Example No. 5.Z
Figure 5-4. Shear failure for surface water collection and removal system.
          C' = climate factor

          L' = field length factor

          V = vegetative cover factor
There are many problems in  maintaining an
agricultural layer on top of a landfill site, especially
in arid or semiarid regions. An agricultural layer
built on a surface water  collection and removal
system composed of well-drained stone and synthetic
material may have trouble supporting crops of any
kind because the soil moisture is removed. In arid
regions,  a continuous  sprinkler system may be
needed to maintain growth on top of the cap, even if
the soil is sufficiently deep and fertile. A final
problem involves landfills built on slopes greater
than 3:1.  Equipment necessary to plant and
maintain crops cannot operate on steeper slopes.
Operators should contact their local agricultural
extension  agent  or  State  Department of
Transportation to find out what kinds of vegetation
will  grow under  the conditions  at  the  site.  The
impact of the SWCR system on the soil layer  also
should be studied before vegetation is chosen. Native
grasses  usually are the best choice because  they
already are adapted to the  surrounding
environment. Sometimes vegetation can overcome
adverse conditions, however. At one site in the  New
Jersey Meadowlands, plants responded to excess
surface water by anchoring to the Underlying waste
through holes in  a  FMC, creating a sturdy bond
between surface plants and underlying material.

For sites on very arid land or on steep slopes, an
armoring system, or hardened cap, may be  more
effective than a vegetative layer for securing a
landfill. Operators  should not depend on an
agricultural layer for protection in areas where
vegetation cannot survive. Many States allow
                                               80

-------
Cell Component: SURF/US L]A

IU 5*4 £4. 0 -TAP*.
TEK ^oUE
—»

^^
. ST^tig^TH of SUJtT R
L
l&c
References:
Example*

*~ C"oVt** ^"U To "SKJcR " 4O°
~ "SkO£(? T> Ft~4£ • 26*
•SuoPt AAJc-jLe. s.i *
* Teuiite Sr«£M
-------
       1500f
                                                   6 osy Geotextile
          EDPM.75 mm      PUC.75 mm
                    CPE.75 mm     HDPE.75 mm
• Geomembrane Alone
0 Geotextile Both Sides
B Geotextile Front
B Geotextile Back
EDPM.75 mm       PUC.75 mm
          CPE.75 mm       HDPE.75 mm
                                                  12 osy Geotextile
           EDPM.75 mm        PUC.75 mm
                    CPE.75 mm       HDPE.75 mm
                       ' EDPM.75 mm      PUC.75 mm
                                 CPE.75 mm     HDPE.75 mm
                                                 • Geomembrane Alone
                                                 O Geotextile Both Sides
                                                 B Geotextile Front
                                                 3 Geotextile Back
                                    |  1111 I      18 osy Geotextile
           EDPM.75 mm       PUC.75 mm
                    CPE.75 mm       HDPE.75 mm
                       1 N = .225 Ib.

                  a. Puncture Resistance
    (Koerner, 1986)
  ' EDPM.75 mm      PUC.75
            CPE.75 mm
             1 J = .738 ft-lb
                                                mm
                                                  HDPE.75 mm
                                 b. Impact Resistance
Figure 5-6.  Puncture and impact resistance of common FMLs.
                                                       82

-------
 Cell  Component: fLe*i»tE.  He.MBg*uE
 Consideration: •SETTLE. ME.MT :  VERIFY J.IHUTY •"•  Fs-»£.  T- *
                 5tTTLtMluT Ke*ULTHJ<5 FROM L*uej-~TCRM UJA*T£
                 5iTTx*Meur nATJ*ts MAY ee  &IA«IAU OA uui*.xi*
 Required Material Properties
   - YltLO OTAIM r»«
           Range
Test
Standard
                                                       ASTM 045=15
 Analysis Procedure:
                   ou 7»«tiTi.tMeuT  *  UA-STE
          (Sj.Ti0
                                                        e.i     o
                                             SETTLEMENT RATIO, S/2t
            PE'  *<*•/<„
 Design Ratio:
         References:
            KMIP-^H IE.LD
                                                                     Example:
                                                 • MIUIMIJM UJlPTH OF ^C LL "" 5O FT
                                                 • DEPTH =F UA»T£ ' eo rr
                                                 .' ^*OMPo»irE
                                             (l ^ E^T'MATE
                                                                                          OF  5fcTTt£MEUT  F"EA
                                                           EMT  PERTH » S'/.*io  - Z
                                                            ETTLEt->EUT  RATIO , SR
                                                             «
                                                             2
                                                             l»
                                                             |
                                                             o
                                                             2 s
                                                             D
                                                                                                                  CltcuUI Tfouih Model
                                                                                                               ^^
                                                                                                  U_
                                                                                                  ^
                                                                                                 OK
                                                                                                              0     0.1     0.1     0.)
                                                                                                               SETTLEMENT RATIO, S/21
                                                                                                            [Example  No. 5.4
Figure 5-7. The effects of settlement on a flexible membrane cap.

-------
                  Steel Clamp
                                         . Mastic
                           Boot Seal at FMC
                      Gasket
                           Flange Seal at FMC




Figure 5-8.  Details of a gas vent pipe system.
                                                             ::;.  .;'.. Perforated Pipe .'.- .'.;. • Gas Vent




                                                                        Operational Cover
                                                          84

-------
Gas Flow
                              Condensate Drain to Collector
                          Gas Flow
                     • Gas Well
                                Condensate Drain to Well
      • Gas Flow
      • Water Flow
 Moisture Control

(after Rovers, et al)
                                                                100%
                                                                                                                     100%
Figure 5-9.  Water traps in a gas collector system.
                                                                              0.2       0.4
                                                                                                 0.6       0.8      1.0

                                                                                               Normalized Pressure Ratio
                                                               Figure 5-10.  Air and water transmissivity in a needle-punched
                                                                            nonwoven geotextile.
                                                                                                   Vegetation
                                                                                                   Topsoil
                                                                                                   (60 cm)
                                                                                                   Gravel Filter
                                                                                                     (30 cm)
                                                                                                   Cobblestone
                                                                                                     (70 cm)
                                                                                                                   Biotic
                                                                                                                   Barrier
                                                                                           '  .'-  •   Protctive Layer

                                                                                           =^==,  FMC
                                                                                                  Compacted Soil
                                                                                                      (90 cm)
                                                                                                  Gas Vent
                                                                                            '.' ' •    (30 cm)
                                                                                                  Waste
                                                               Figure 5-11. Optional biotic barrier layer.
                                                           85

-------
                   =5
                                 100
Figure 5-12. Soil erosion due to slope.
                                           200
300
                                                              400
                                                                       500
                                                                                 600
                                                                                           700
                                                                                                    800
                                                      Slope Length (Feet)
                                                           86

-------
Figure 5-13.  Regional depth of frost penetration in inches.
              Extrusion Weld
                       \
                                                                                                         FMC
                    Extrusion Weld
Figure 5-14. Geosynthetic cell profile with extrusion welds at FML and FMC junctures.
                                                         87

-------

-------
                6.  Construction, Quality Assurance, and Control:
                              Construction of Clay Liners
Introduction
This chapter focuses on construction criteria for clay
liners, including important variables in soil
compaction, excavation and placement  of  liner
materials, and protection of liners after construction.
The chapter concludes with a discussion of
construction quality assurance, and of test fills and
their incorporation into the design and construction
quality assurance plan for liners.

Compaction Variables
The most important variables in the construction of
soil liners are the compaction variables: soil water
content, type of compaction, compactive effort, size of
soil clods,  and  bonding between lifts.  Of these
variables, soil water content is  the most critical
parameter.

So/7 Water Content
Figure 6-1  shows the influence of molding water
content (moisture content of the soil  at the time of
molding or compaction) on hydraulic conductivity of
the soil. The lower half of the diagram is a
compaction curve and shows the  relationship
between dry unit weight, or dry density of the soil,
and water content of the soil. A water content called
the optimum moisture content is related to a peak
value of dry density, called a maximum dry density.
Maximum dry density is achieved at the optimum
moisture content.

The smallest  hydraulic  conductivity of the
compacted  clay  soil usually occurs when the soil is
molded at a moisture content slightly higher than
the optimum moisture content. That minimum
hydraulic conductivity value can occur anywhere in
the range of 1 to 7 percent wet of optimum water
content.  Ideally,  the liner should be  constructed
when the water content of the soil is wet of optimum.

Uncompacted clay soils that are dry of their optimum
water content contain dry hard clods that are  not
easily broken  down during  compaction. After
     Hydraulic
    Conductivity
     Dry Unit
     Weight
Figure 6-1.
            Molding Water Content

Hydraulic conductivity and dry unit weight as a
function of molding water content.
compaction, large, highly permeable pores are left
between the clods. In contrast, the clods  in  wet
uncompacted soil  are soft and weak.  Upon
compaction, the clods are remolded  into  a
homogeneous relatively impermeable mass of soil.

Low hydraulic conductivity is the single most
important factor in constructing soil liners. In order
to achieve that low value in compacted soil, the large
voids or pores between the clods must be destroyed.
Soils are compacted while wet because the clods can
best be broken down in that condition.

Type of Compaction
The method used to compact the soil is another
important factor in achieving  low hydraulic
conductivity. Static compaction is a method by which
soil packed in a mold is squeezed with a piston to
                                               89

-------
compress the soil. In kneading compaction, a probe or
pie-shaped metal piece is pushed repeatedly into the
soil. The kneading action remolds the soil much like
kneading bread dough.  The kneading method is
generally  more successful in breaking down clods
than is the static compacting method (see Figure 6-
2).
            ID'5
             ID'6
        1
             10-7
             10-8
    Optimum w    —
                               Static
                               Compaction
                  Kneading Compaction
                  15
  19      23

Molding w (%)
                                         27
 Figure 6-2.  Efficiencies of kneading compaction and static
           compaction.
The best type of field compaction equipment is a
drum roller (called a sheepsfoot roller) with rods, or
feet, sticking out from the drum that penetrate the
soil, remolding it and destroying the clods.

Compactive Effort
A third compaction  variable to consider is
compactive effort. The lower half of the diagram in
Figure 6-3 shows that increased compactive effort
results in increased maximum density of the soil. In
general, increased compactive  effort also reduces
hydraulic conductivity.  For  this reason, it is
advantageous to use heavy compaction  equipment
when building the soil liner.

Two samples of soils with the same water content
and similar  densities  can have vastly different
hydraulic conductivities when compacted with
different energies. The extra compaction energy may
                                                             12
                                                                        16         20
                                                                     Molding Water Content (%)
                                                   Figure 6-3. Effects of compactive effort on maximum density
                                                            and hydraulic conductivity.
                           not make the soil more dense, but it breaks up the
                           clods and molds them together more thoroughly.

                           The compaction equipment also  must pass over the
                           soil liner a sufficient number of times to maximize
                           compaction.  Generally, 5  to  20 passes  of the
                           equipment over a given lift of soil ensures that the
                           liner has been compacted properly.

                           A set of data for clay with a plasticity index of 41
                           percent used in a trial pad in Houston illustrates two
                           commonly used compaction methods. Figure 6-4
                           shows the significantly different compaction curves
                           produced by standard Proctor and modified Proctor
                           compaction procedures. The  modified Proctor
                           compaction technique uses about five times more
                           compaction energy than the standard Proctor.

                           Figure 6-4 shows the hydraulic conductivities of the
                           soil molded at 12 percent water content to be less
                           than 10-!0 cm/sec, using the modified Proctor, and
                           10-3 cm/sec, using the standard Proctor. The different
                           levels of compaction energy produced a seven order of
                           magnitude difference in hydraulic conductivity.
                           Apparently, modified Proctor compaction provided
                           enough energy to destroy  the clods and produce low
                                                90

-------
   hydraulic conductivity, whereas standard Proctor
   compaction did not.

   Figure 6-4 also  shows that at  20 percent molding
   water content, the soil's water content and density
   are virtually the same when  packed with  either
   modified or standard Proctor equipment. Modified
   Proctor compaction, however, still gave one order of
   'magnitude  lower hydraulic conductivity. In  this
   case, additional compaction energy  produced
   significantly lower hydraulic conductivity without
   producing greater density.
              130
                        10      15      20

                      Molding Water Content (%)
25
         moisture content between the soil that was crushed
         and passed through a No. 4 sieve and the soil that
         merely was passed through a 0.75-inch sieve. .The
         implication for laboratory testing is that the
         conditions of compaction  in the  field must be
         simulated as closely as possible in the laboratory to
         ensure reliable results.
                                                               c
                    135
                                                                  125
                                                                  115
                                                                  105
                                                                   95
                                                                   85
                                                                                    0.2-in. Clods
                                                                                    0.75-in. Clods
                                                                     10        15        20

                                                                           Molding Water Content (%)
                                                    25
                                                       Figure 6-5.  Effects of clod size on hydraulic conductivity.
    Figure 6-4. Effects of modified Proctor versus  standard
             Proctor compaction procedures.
   Size of Clods
   Another factor that affects hydraulic conductivity is
   the size of soil clods. Figure 6-5 shows the results of
   processing the same  highly plastic  soil from a
   Houston site in two ways. In one, the soil was passed
   through the openings of a 0.75-inch sieve, and in the
   other, the soil was ground  and crushed to pass
   through a 0.2-inch  (No. 4) sieve. Most geotechnical
   laboratories performing  standard  Proctor
   compaction tests first air dry, crush, and pulverize
   the soil to pass through a No. 4 sieve, then moisten
   the soil to various water contents before compaction.
   Figure 6-5 shows a 3 percent difference in optimum
        Table 6-1 summarizes data concerning the influence
        of clod size on hydraulic conductivity for the same
        soil. At  a molding water content of 12 percent,
        hydraulic conductivity of the  sample  with the
        smaller  (0.2-inch) clods  is about four orders  of
        magnitude lower than the hydraulic conductivity for
        the sample with larger (0.75-inch) clods. Apparently,
        at 12 percent water content, the clods are strong, but
        when reduced in size, become weak enough to be
        broken down by the compaction process.  For the wet
        soils with a molding water content of 20 percent, clod
        size appears to have  little influence on hydraulic
        conductivity, because the soft, wet clods are easily
        remolded and packed more tightly together. Clod size
        then is an important factor in dry, hard soil, but less
        important in wet, soft soil, where the clods are easily
        remolded.
_
                                                    91

-------
Table 6-1.  Influence of Clod Size on Hydraulic Conductivity
               Fully-Penetrating Feet:
Molding
W.C. (%)
12
16
18
20
Hydraulic
0.2-in. Clods
2x 10-8
2x10-9
1 x 10-9
2x10-9
Conductivity (cm/s)
0.75-in. Clods
4x 10-4
1 x 10-3
8 x 10-'Q
7x 10-'°
Bonding between Lifts
A final important compaction variable is the extent
of bonding between lifts of soil. Eliminating highly
permeable zones between  lifts cuts off  liquid flow
from one lift to another. If defects in one lift can be
made discontinuous with defects in another lift, then
hydraulic continuity between lifts can be destroyed
(see Figure 6-6).
               I
 Figure 6-6.  Conductivity between lifts.
Compaction equipment with rollers that knead or
remold the soil can help destroy hydraulic connection
between defects. Footed rollers are  the best kind to
use for this purpose. The two kinds of footed rollers
generally used for soil compaction are those with
long, thin feet that fully penetrate the soil and those
with feet that  only partially penetrate the soil (see
Figure 6-7). The roller with fully penetrating feet,
typically called a sheepsfoot roller, has shafts about 9
inches long. Because the lift thickness of a clay liner
is typically 8 to 9 inches before compaction and 6
inches after compaction,  the shaft of the sheepsfoot
roller can push through an entire lift of soil.

The fully penetrating feet go all the  way through the
loose lift of soil to  compact the bottom of the lift
directly into the top of the previously compacted lift,
blending the new lift in with the  old. The partly
penetrating foot, or padfoot, cannot blend the new lift
                                                                                             Loose Lift
                                                                                               of Soil
                                                                        /  /  X  /  X
                                                                     Compacted Lift
                                                                  /  s  / /  /  /
              Partly-Penetrating Feet:
                                                                                              Loose Lift
                                                                                               of Soil
                                                                       / X  X  /^
                                                                     Compacted Lift
                                                      Figure 6-7. Two kinds of footed rollers on compaction
                                                               equipment.
to the old, since  its shorter shafts  do not  go
completely through the lift.

Another way to blend the new lift with the old lift is
to make the surface of the previously compacted lift
very rough. Commonly in the construction of soil
liners, the finished surface of a  completed lift is
compacted with a smooth,  steel drum roller to seal
the surface of the completed lift. The smooth soil
surface of the completed lift minimizes desiccation,
helps prevent erosion caused by runoff from heavy
rains, and helps in quality control testing. The soil,
however, must be broken up with a disc before a new
lift of soil can be placed over it.

In below-ground disposal pits,  it  is  sometimes
necessary to construct a soil liner on the side slopes.
This sloping clay liner component can be constructed
either with lifts parallel to the face of the soil or with
horizontal lifts (see Figure 6-8). Horizontal lifts  must
be at least the width of one construction vehicle, of
about 12 feet.

Horizontal lifts can be constructed on almost any
slope, even one that is almost vertical. Parallel lifts,
however,  cannot be constructed on slopes at angles
steeper than about 2.5 horizontal to 1 vertical (a
                                                  92

-------
                                                          Parallel Lifts
                                                                                         Sandy Soil
       Horizontal Lifts
Figure 6-8.  Liner construction on side slopes with horizontal
          and parallel lifts.
                                                          Horizontal Lifts
                                                                                        Sandy Soil
 Figure 6-9.
Effect of sandy soil zone on liners with parallel
and horizontal lifts.
slope angle  of about 22  degrees),  because  the
compaction equipment cannot operate on them.

On surfaces without steep  slopes, soil liners with
parallel lifts are less sensitive to some of the defects
that might occur during construction than those
built with horizontal lifts. Figure 6-9  shows a liner
containing a quantity of  sandy material. With
parallel lifts, the sandy zone is surrounded by zones
of good soil, and so  has  little influence. But with
horizontal lifts, a window through the soil liner could
allow greater permeability to waste leachate if it
were to occur on the bottom in a sump area.


Compaction Equipment
In addition to increasing bonding between lifts (as
discussed in the previous section), the equipment
used  to  compact  soil liners should maximize
compactive energy and the remolding capability of
the soil. The type of roller,  weight of the roller, and
number of passes the  equipment makes  over  the
surface of the soil are all  important factors. The
heaviest rollers available weigh between 50,000 and
70,000 pounds. The Caterpillar 825 is an example of
one of the heaviest, weighing more than  50,000
pounds and having long, penetrating feet. A medium
weight roller weighs between 30,000 and  50,000
pounds and a relatively light roller weighs 15,000 to
30,000 pounds.
The best way to compare one roller to another is to
examine weight per linear foot along the drum
surface. A very lightweight roller will  typically
weigh about 500 pounds per linear foot along the
drum surfaces, while a very heavy roller  weighs
3,000 to 5,000 pounds per linear foot.

Vibratory rollers,  weighing typically 20,000 to
30,000 pounds static weight may not be effective for
clay compaction. A piece of vibration equipment
inside the drum gives the vibratory roller its name.
The drums of static rollers are  filled  with liquid,
making them very heavy. The vibratory equipment
inside the drum of the  vibratory roller,  however,
prevents it from being filled with water, so the total
weight is in the drum itself. This kind of roller works
well for  compacting granular base materials beneath
pavements,  so contractors frequently  have them
available. However, there is no  evidence that the
high frequency of vibration is effective in compacting
clay.

Vibratory rollers are not good rollers for compacting
clay liner materials for several  reasons. First, the
padfoot  (only about 3 inches long) does  not fully
penetrate the  soil. Second, the area of the foot is
fairly large. Because the weight is spread over a
large area, the stresses are smaller and the soil is not
compacted as effectively. The smaller the area of the
foot, the more effective in remolding the soil clods.
Third, the roller is relatively lightweight, weighing
                                                93

-------
only  20,000  to 30,000  pounds. In  addition,
approximately half the rollers' weight goes to the
rear axle and the rubber tires, leaving only about
15,000 pounds or less to be delivered to the drum.

The feet of a classic sheepsfoot roller, in contrast to
those of the vibratory roller, are about 9 inches long.
The area of the foot is relatively small so that the
compact stress on the tip typically ranges from 200 to
700 pounds per square inch. The drum normally is
filled with liquid so that great weights are achieved
directly on the drum. Manufacturers make very few
sheepsfoot rollers now, despite the fact that they are
the most effective roller for clay compaction. The
Caterpillar 815 and 825 are two of the few sheepsfoot
rollers currently being produced.

The  Construction  Process
Table 6-2 outlines the major steps in the construction
process for clay liners. First, a source of soil to be
used  in constructing the liner must be found. Then
the soil is excavated at this location from a pit called
a "borrow pit."  (Excavated soil is referred to as
"borrow soil.") Digging tests pits in the borrow area
helps determine the stratification of the soil before
beginning excavation of the borrow pit itself.

      Table 6-2.  Steps in the Construction Process

  1. Location of Borrow Source
     — Boreholes, Test Pits
     — Laboratory Tests
  2. Excavation of Borrow Soil
  3. Preliminary Moisture Adjustment; Amendments; Pulverization
  4. Stockpile; Hydration; Other
  5. Transport to Construction Area; Surface Preparation
  6. Spreading in Lifts; Breakdown of Clods
  7. Final Moisture Adjustment; Mixing; Hydration
  8. Compaction; Smoothing of Surface
  9. Construction Quality Assurance Testing
 10. Further Compaction, If Necessary	

The borrow soil is mixed  and blended as  it  is
excavated to produce as homogeneous a soil as
possible. Scrapers  are useful for excavating  soils
from borrow areas, because the soil is mixed up in
the scraper pan by the action of the scraper. The soil
also can be sieved and processed through a rock
crusher to grind down hard clods.  Cutting across
zones of horizontal stratification also  will help mix
up the  soil as it is excavated. Using some of these
methods, the excavation process can be  designed to
maximize soil mixing  without significantly
increasing excavation costs.

The next step is to moisten or dry the soil as needed.
If the required change in water content is only 1 to 2
percent, the adjustment in moisture content can be
made after the soil is put in place and before it is
compacted. However, if a substantial change in soil
moisture content is necessary, it should be performed
slowly so moistening occurs uniformly throughout
the soil. To change the soil moisture content, the soil
is spread evenly  in  a layer, moistened,  and  then
covered  for several days,  if possible, while the
moisture softens the soil clods. A jdisc or a rototiller
passed through the soil periodically speeds up the
process.

If soil moisture content is too high, the soil should be
spread in lifts and allowed  to dry. Mixing the soil
during the drying process will prevent a dry crust of
soil  from forming  on th.e  top  with  wet  soil
underneath.

When the moisture adjustments have been made, the
soil is transported to the construction area. Then the
soil is spread in lifts by bulldozer or scraper, and a
disc  or rototiller  is used to break down  soil clods
further. A pulvermixer, a piece of equipment widely
used  for reclaiming asphaltic concrete pavement,
also  works well. These  machines can pulverize and
mix a lift of soil as much as 24 inches deep.

Once the soil  is in place and prior to compaction,
minor adjustments in moisture content again can be
made. No large changes in water content should  be
made at this time, however.

In the next step,  the soil is  compacted. Afterwards,
the surface of the soil may be smoothed by a smooth
steel drum roller before the construction quality
control inspector performs the moisture density test.
If the test indicates that the  soil has been compacted
adequately, the next lift is placed on top of it. If the
compaction has not been performed properly, the soil
is either compacted further or  that  section of the
liner is dug up and replaced.

Soil-Bentonite Liners
When there is not enough clay available at a site to
construct a soil liner, the clay  can be mixed with
bentonite. The amount of bentonite needed should be
determined in the laboratory and then adjusted to
account for any irregularities occurring during
construction. Dry bentonite is mixed with the soil
first, and water is  added  only after the mixing
process is complete.

The  bentonite can be mixed using a pugmill or  by
spreading the soil in lifts and placing the bentonite
over the surface. Passing a  heavy-duty pulvermixer
repeatedly through the soil  in both directions mixes
the soil with the bentonite.  After the bentonite and
clay are mixed, water  is added in small amounts,
with the soil mixed well after each addition. When
the  appropriate  moisture  content is reached, the
clay-bentonite soil is compacted.
                                                  94

-------
After the construction process is finished, the newly
compacted soil liner, along with the last lift of soil,
must be covered to protect against desiccation or
frost action, which can crack the soil liner.
Construction Quality Assurance (CQA)
Testing
Construction quality assurance (CQA) control tests
must be performed on the finished liner. There are
two categories of CQA tests: tests on the quality of
the material used in construction,  and tests on the
completed lift soil to ensure that proper construction
has taken place. These tests include:

Materials Tests:

• Atterberg Limits
• Grain Size Distribution
• Compaction Curve
• Hydraulic Conductivity of Lab-compacted Soil

Tests on Prepared and Compacted Soil:

• Moisture Content
• Dry Density
• Hydraulic Conductivity of "Undisturbed" Sample

Table  6-3  presents  recommendations for  testing
frequency at municipal solid waste landfills. This
table was developed by the Wisconsin Department of
Natural Resources and is also contained in the EPA's
technical resource document on clay liners.

Tests on prepared and compacted soils often  focus on
water content and soil density.  Construction
specifications  usually require minimums  of  95
percent of maximum density with  standard Proctor
compaction or 90 percent of maximum density with
modified  Proctor  compaction.  Acceptable
percentages of water content commonly range from 1
to 5 percent higher than optimum moisture content.

Figure 6-10 shows a typical window of acceptable
ranges  for  percentages of water  content and
minimum  density. Typical data for water  content
and density gathered in the laboratory are plotted in
Figure 6-11. The solid data points represent samples
for which the hydraulic conductivities were less than
 10-7 cm/sec. The open symbols correspond to samples
 that have hydraulic conductivities greater than 10-7
 cm/sec. The window of acceptable moisture  contents
 and densities includes all of the solid data points and
 excludes all of the open data points. Such a window
 defines acceptable moisture content/density
 combinations with  respect  to  methods of soil
 compaction (modified Proctor or standard Proctor).
The window in Figure 6-10 is actually a subset of the
window in Figure 6-11.

Defining a window of acceptable water contents and
densities for hydraulic conductivity  is  a
recommended first step in developing construction
specifications. Someone designing a clay liner might
choose just a small part of an acceptable range such
as that defined  in  Figure 6-11. For example,
extremely high water content may be excluded to
establish an upper water content limitation because
of concerns over the strength of the soil. In an arid
region, where wet soil can dry up and desiccate, the
decision might be made to use only materials at the
dry end of the range.

Factors  Affecting  Construction Quality
Assurance (CQA) Control Testing
Key  factors that  affect  construction quality
assurance control testing include sampling patterns,
testing bias, and outliers,  or data that occurs outside
of the normally accepted range.

The first  problem in  construction quality  control
testing is deciding where to sample. Some  bias  is
likely to  be introduced  into a sampling pattern
unless a completely random sampling pattern  is
used. For random sampling, it is useful to design a
grid pattern with about 10 times  as many grids as
samples to be taken. A random number generator,
such as those on many pocket calculators, can be
used to pick the sampling points.

Bias in test results can originate from many areas, so
it is important to include  in a CQA plan a procedure
for verifying test results. Nuclear density and
moisture content tests, for example, can err slightly.
The CQA plan should specify that  these tests will be
checked with other tests on a prescribed frequency to
cut bias to a minimum.  Certain  "quick" moisture
content tests, such as tests using a microwave oven
to dry soil, can also be biased. The plan must specify
that these kinds of tests be cross-referenced
periodically to more standard tests.

Clay content and hydraulic conductivity tests on so-
called "undisturbed" samples of soil often give little
useful information. To obtain accurate results, the
conditions of the tested sample must match the field
conditions as closely as possible. In the Houston test
pad, for example, laboratory tests on 3-inch diameter
tube samples gave results that differed by five orders
of magnitude from the field value.

Inevitably, because soil is a variable material, some
data points will be outside the acceptable range. The
percentage of such points,  or outliers, that will be
allowed should be determined in advance of testing.
Figure 6-12 shows that if enough data points define a
                                                 95

-------
 Table 6-3. Recommendations for Construction Documentation of Clay-Lined Landfills by the Wisconsin Department of Natural
          Resources
                   Item
                                                        Testing
                                                         Frequency
  1.  Clay borrow source testing
  2.  Clay liner testing during construction
  3. Granular drainage blanket testing
    Grain size
    Moisture
    Atterberg limits (liquid limit and plasticity
     index)
    Moisture-density curve
    Lab permeability (remolded samples)
    Density (nuclear or sand cone)
    Moisture content
    Undisturbed permeability
    Dry density (undisturbed sample)
    Moisture content (undisturbed sample)
    Atterberg limits (liquid limit and plasticity
     index)
    Grain size (to the 2-micron particle size)
    Moisture-density curve (as per clay borrow
     requirements)
    Grain size (to the No. 200 sieve)
    Permeability
1,000 yd3
1,000 yd3
5,000 yd3           ;
5,000 yd3 and ail changes in material
10,000 yd3
5 tests/acre/lift (250 yd?)
5 tests/acre/lift (250 yd3)
1 test/acre/lift (t,500 yd3)
1 tesVacre/lift (1,500 yd3)
1 test/acre/lift (1,500 yd3)
1 tesVacre/lift (1,500 yd3)

1 test/acre/lift (1,500 yd3)
5,000 yd3 and all changes in material
1,500 yd3
3,000 yd3
 Source:  Gordon, M. E., P. M. Huebner, and P. Kmet. 1984. An evaluation of the performance of four clay-lined landfill^ in Wisconsin.
         Proceedings, Seventh Annual Madison Waste Conference, pp. 399-460.
          Yd

        (Yd)miix


    0.95{Yd)max
                               Zero Air Voids
Acceptable
  Range
                           W,
                             'opt
                 W
 Figure 6-10.  Acceptable  range  for  water  content and
             minimum densities.
                    Acceptable
                    Range
                                                                               Molding Water Content
                        Figure 6-11. Molding water  contents and densities  from
                                    Houston test pad.
normal distribution,  allowing for  a percentage of
outliers, the acceptable  minimum value for  a
parameter can be determined.
Test Fills
Test fills simulate the actual conditions of soil liner
construction before the full-sized liner  is built.
                        Generally, they are approximately 3 feet thick, 40 to
                        80 feet long, and 20 to 40 feet wide. The  materials
                        and construction practices for a  test  fill should
                        imitate  those proposed for the full-sized  liners as
                        closely as possible. In situ hydraulic conductivity of
                        the soil at the test pad is required to confirm that the
                        finished liner will conform to regulations.  A sealed
                        double-ring infiltrometer  usually  is used for  this
                                                         96

-------
                          Mean

                      Value of Parameter
     Minimum
   d)
   
-------
                Collection
                Pit
                                         Gravel to Load Clay
                                         to Evaluate Effect of
                                         Overburden Stress
                                Compacted Clay
                                                          )         V
                                   Collection Pan Lysimeter XI        > i inHorHrai:
      Underdrain


Geomembrane
                                     To Collection
                                     Pit
Figure 6-13.  An Ideal test pad.
                                                             98

-------
            7.  CONSTRUCTION  OF FLEXIBLE MEMBRANE LINERS
Introduction
This chapter describes the construction of flexible
membrane liners (FMLs), quality control measures
that should be taken during construction, and EPA's
construction quality assurance (CQA) program. The
CQA program for FMLs  is a planned series of
activities performed by the owner of a hazardous
waste facility to ensure that the flexible membrane
liner is constructed as specified in the design. There
are five elements to a successful CQA program: (1)
responsibility and authority,  (2) CQA personnel
qualifications, (3) inspection activities, (4)  sampling
strategies, and (5) documentation. This chapter
discusses each of these elements.

Responsibility and Authority
A FML may be manufactured by one company,
fabricated by a second company, and installed by a
third company. The FML also may be manufactured,
fabricated, and  installed  by the same company.
Depending on how the FML is constructed, various
individuals  will  have  responsibilities within the
construction process. These individuals may include
engineers, manufacturers, contractors, and owners.
In general, engineers design the components  and
prepare specifications,  manufacturers fabricate the
FML, and contractors perform the installation.

Any company that installs a FML should  have had
past experience with at least 10 million square feet of
a similar FML material. Supervisors  should  have
been responsible for installing at least  2 million
square feet of the FML material being installed at
the facility. Caution should be exercised in selecting
firms to install FMLs since  many companies  have
experienced  dramatic growth in the last several
years and do not have  a  sufficient number of
experienced senior supervisors.

A qualified auditor should be employed to review two
 key documents:  (1) a checklist of requirements for
facilities, which will help ensure that all facility
 requirements are met; and (2) a CQA  plan, which
will be  used  during construction to  guide
observation, inspection, and testing.

Designers are responsible for drawing up general
design specifications. These specifications indicate
the type of raw  polymer and manufactured sheet to
be used, as well  as  the limitations  on delivery,
storage, installation, and sampling. Some specific
high density polyethylene (HOPE) raw polymer and
manufactured sheet specifications are:

   Raw Polymer Specifications

   • Density (ASTM D1505)
   • Melt index (ASTM D1238)
   • Carbon black (ASTM D1603)
   • Thermogravimetric analysis (TGA) or differ-
     ential scanning calorimetry (DSC)

   Manufactured Sheet Specifications

   • Thickness (ASTM D1593)
   • Tensile properties (ASTM D638)
   • Tear resistance (ASTM D1004)
   • Carbon black content (ASTM D1603)
   • Carbon black disp. (ASTM D3015)
   • Dimensional stability (ASTM D1204)
   • Stress crack resistance (ASTM D1693)

 Both the design specifications and the CQA plan are
 reviewed during a preconstruction CQA meeting.
 This meeting is the most important part of a CQA
 program.

 The preconstruction meeting also is the time to
 define criteria for "seam acceptance."  Seams are the
 most difficult aspect of field construction. What
 constitutes an acceptable seam should be defined
 before the installation gets under way. One
 technique is to define seam acceptance and verify the
                                                99

-------
qualifications of the personnel installing the seams
at the same time. The installer's seamers produce
samples of welds during the preconstruction CQA
meeting that are then tested to determine seam
acceptability. Samples of "acceptable" seams are
retained by both the owner and the installer in case
of disputes later on. Agreement on the  most
appropriate repair  method also should be  made
during the preconstruction CQA meeting. Various
repair methods may be used, including capstripping
or grinding and re welding.

CQA Personnel Qualifications
EPA requires that the CQA officer be a professional
engineer (PE),  or the equivalent,  with sufficient
practical,  technical, and managerial experience.
Beyond these basic criteria, the CQA officer must
understand the  assumptions made in  the design of
the facility and the installation requirements of the
geosynthetics. Finding personnel with the requisite
qualifications and actual field  experience can be
somewhat difficult. To develop field expertise in
landfill CQA, some consulting firms routinely assign
an inexperienced engineer to work with trained CQA
people on a job site and not bill for the inexperienced
engineer receiving training. This enables companies
to build up a reservoir of experience in a short period
of time.

Inspection Activities
Because handling and  work in the field can damage
the manufactured sheets, care must be taken when
shipping, storing, and  placing FMLs. At every step,
the material should be carefully checked for signs of
damage and defects.

Shipping and Storage Considerations
FML panels frequently are fabricated in the factory,
rather than on site. The panels must be shipped and
stored carefully. High crystalline FML, for example,
should not be folded for shipment. White lines, which
indicate stress failure,  will develop if this material is
folded. Flexible membrane liners that  can be folded
should be placed on pallets when being shipped to the
field. All FMLs should be covered during shipment.
Each shipping roll should be identified properly with
name of manufacturer/fabricator, product type and
thickness,  manufacturer batch  code,  date of
manufacture, physical dimensions, panel number,
and directions for unfolding.

Proper onsite storage also must be provided for these
materials.  All FMLs should be stored in a secure
area, away from dirt, dust, water, and extreme heat.
In addition, they should be placed where people and
animals cannot disturb them. Proper storage
prevents  heat-induced bonding  of the  rolled
membrane  (blocking), and loss of plasticizer or
curing of the polymer, which could  cause
embrittlement of the membrane and subsequent
seaming problems.

Bedding Considerations
Before placing the membrane, bedding preparations
must be completed. Adequate compaction (90 percent
by  modified proctor equipment; 95  percent  by
standard proctor equipment) is a must. The landfill
surface must be free of rocks, roots, and water. The
subgrades should be rolled smooth and should be free
from desiccation cracks. The use of herbicides can
also affect bedding.  Only chemically compatible
herbicides should be  used, particularly in surface
impoundments. Many herbicides have hydrocarbon
carriers that will react  with the membranes and
destroy them.

FML Panel Placement
Prior to unfolding or unrolling, each panel should be
inspected carefully for  defects. If no  defects are
found,  the panels may be unrolled. The delivery
ticket  should describe how to unroll each panel.
Starting with the unrolling process, care  should be
taken to minimize  sliding of the panel.  A proper
overlap for welding should be allowed as each panel
is placed. The amount of panel placed should be
limited to that which can be seamed in 1 day.

Seaming and  Seam  Repair
After the panels have been inspected for defects, they
must be seamed by a  qualified seamer. The
membrane must be clean for the seaming process and
there must be a firm  foundation beneath  the seam.
Figure 7-1 shows the configuration of several types of
seams.

The most important seam repair criterion is that any
defective seam must be bounded by areas  that pass
fitness structure tests. Everything between such
areas must be repaired. The repair method should be
determined and agreed upon  in advance, and
following a repair, a careful visual inspection should
be performed to ensure the repair is successful.

Weather and Anchorage Criteria
Weather is an additional consideration  when
installing a FML. From the seaming standpoint, it is
important not to expose the liner materials to rain or
dust. Any time the temperature  drops below 50°F,
the  installer  should  take  precautions for
temperature. For example, preheaters  with the
chambers around them may be used in cold weather
to keep the  FML warm. There also should  be  no
excessive wind, because  it is very difficult to weld
under windy conditions.

In addition, FML panels should be anchored as soon
as possible. The anchor trench may remain open for
                                              100

-------
    Lap Seam

    Lap Seam with Gum Tape
                                     Adhesive
                                    Gum Tape
  Tongue and Groove Splice

 Factory
Vulcanized \JS5S!
     Extrusion Weld Lap Seam
     Fillet Weld Lap Seam
                                        Tape

      Double Hot Air or Wedge Seam
 Figure 7-1.  Configurations of field geomembrane seams.
several days after installation of a panel. However,
the anchor trench must be filled when the panel is at
its coolest temperature and is, therefore, shortest in
length. This will occur early in the morning.

Additional Polymer Components
Polymer components, such as.geotextiles, geonets,
and geogrids, must be carefully inspected, as there is
no CQA program for these components. Chapter
Four discusses polymer components  in more detail.
To date, CQA activities have focused on FMLs,  and
there is no way to "fingerprint" other materials to
determine their characteristic properties over the
long term. Fingerprinting refers to the evaluation of
the molecular structure of the polymer. For example,
some  geonets sold on the market use air-entrained
polymers to create "foamed" geonets with greater
thicknesses. Over time,  however, the air -in  the
entrained bubbles diffuses through the polymer and
the drainage net goes flat. When loads are  left on
these geonets for testing purposes, it is possible to
observe orders-of-magnitude  reductions  in  the
capacity of these materials by the 30th day of testing.

Geotextiles, geogrids, and geonets all should be
purchased  from companies that  have instituted
quality control  procedures at their plants  and
understand the  liabilities,  the risks, and the
problems associated with landfill liner failure.

Sampling Strategies
In a CQA program, there are  three  sampling
frequency criteria: (1) continuous  (100 percent), (2)
judgmental, and (3) statistical. Every FML seam
should be tested over 100 percent of its length. Any
time a seaming operation begins, a sample should be
cut for testing. A sample also should be  taken any
time a seaming operation is significantly modified
(by using a new seamer or a new  factory extrusion
rod, or by making  a major  adjustment  to the
equipment).

Continuous (100 Percent) Testing
There  are  three types of continuous tests:  visual,
destruct  (DT), and  nondestruct (NDT).  Visual
inspection must be done on all seams,  and DT tests
must be done on all startup seams.

There  are several types of nondestruct (NDT) seam
tests (see Table 7-1). The actual NDT test depends on
the seam type  and membrane polymer. An air lance
(a. low pressure blast of air focused  on the edge of the
seam)  can be  used on polyvinyl  chloride  (PVC),
chlorinated polyethylene (CPE), and other flexible
liner materials. If there is a loose bond, the air lance
will pop the seam open.

In a mechanical point stress test, a screwdriver or a
pick is pressed into the edge of the seam  to detect a
weak bond location. In a vacuum  chamber test, the
worker applies soapy water to the seam. The vacuum
chamber is then moved over the seam. If there is a
hole, the vacuum draws air from beneath the
membrane, causing a bubble to occur. The chamber
should not be moved too quickly across the seam. To
be effective, the vacuum box should remain on each
portion of the  seam at least 15 seconds before it is
moved. Otherwise, it may not detect any leaks.

The pressurized dual seam test checks  air retention
under pressure. This test is used with double hot air
or wedge seams that have two parallel welds with an
air space between them, so that air pressure can .be
applied between the welds. Approximately 30 psi is
applied for 5 minutes with a successful seam losing
no more than 1 psi in that time. This seam cannot be
used in sumps or areas in which there  is limited
space for the equipment to operate.

Ultrasonic equipment also may be used in a variety of
seam tests. This equipment  measures the  energy
transfer across a  seam using  two  rollers: one that
transmits a high frequency signal, and one that
receives it. An oscilloscope shows the  signal being
received. An anomaly in the signal indicates some
change in properties,  typically a void (caused by the
                                               101

-------
Overgrind of an extruded seam.


presence  of water). Ultrasonic equipment, however,
will not detect a tacked, low-strength seam or dirt
contamination, and the tests are very operator-
dependent.

Judgmental Testing
Judgmental  testing involves a  reasonable
assessment of seam strength by a trained operator or
CQA inspector. Judgmental testing is required when
a visual inspection detects factors such as apparent
dirt, debris, grinding, or moisture that may affect
seam quality.

Statistical Testing
True statistical testing is  not used in evaluating
seams; however, a minimum of one DT every 500 feet,
of seam, with a minimum  of one test per seam,  is
required. Sumps or ramps, however, may have seams
that are very short, and samples should not be cut
from these seams unless they appear defective. In
                                               102

-------
Table 7-1.  Overview of Nondestructive Geomembrane Seam Tests
Nondestructive Test Primary User

1,
2.


3.



4.


5.

6.

7.

Method contrac-
tor
Air lance Yes
Mechanical Yes
point (pick)
stress
Vacuum Yes
chamber
(negative
pressure)
Dual seam Yes
(positive
pressure)
Ultrasonic pulse
echo
Ultrasonic
impedance
Ultrasonic
shadow
Engr.
Insp.
--
--


Yes



Yes


Yes

Yes

Yes

Third Cos'fbf-y
Party Equipment
Inspector ($)
200
Nil


1000



200


Yes 5000

Yes 7000

Yes 5000

Speed of-
Fast
Fast


'Slow



Fast


Mod.

'Mod.

Mod.

General
Cost of
Tests
Nil
Nil


V. high



Mod.


High

High

High

Comments
Type of
Result
Yes-No
Yes-No


Yes-No



Yes-No


Yes-No

Qualitative

Qualitative


Recording
Method
Manual
Manual


Manual



Manual


Automatic

Automatic

Automatic


Operator
Dependency
V. high
V. high


High



Low


Moderate

Unknown

Low

 Source:  Koerner, R. M. and G. N. Richardson. 1987. Design of geosynthetic systems for waste disposal. ASCE-GT Specialty Conference,
        Geotechnical Practices for Waste Disposal, Ann Arbor, Michigan.
 addition, a minimum of one DT test should be done
 per shift.

 There are no outlier criteria for statistical testing of
 seams.  In other words, no  failure is acceptable.
 Typically two tests, a shear test and a peel test, are
 performed on a DT sample (Figure 7-2). The shear
 test measures the continuity of tensile strength in a
 membrane. It is not, however, a good indicator of
 seam quality. The peel  test  provides  a good
 indication of the quality of a weld  because it works
 on one face of a weld. A poor quality weld will fail
 very quickly in a peel test.

 In a shear test, pulling occurs in  the plane of the
 weld. This is comparable  to grabbing onto  the
 formica on a desk top and trying to pull the formica
 off horizontally. The bond is being sheared. The peel
 test, on the other hand, is a true test of bond quality.
 This test is  comparable to getting beneath the
 formica at one corner of a desk top and peeling up.

 Documentation
 Documentation is a very important part of the CQA
 process. Documents must be maintained throughout
 FML placement, inspection,  and testing. A FML
 panel placement log (Figure 7-3),  which details the
 panel  identity, subgrade conditions, panel
 conditions, and seam details, should be kept for every
 panel that is placed. This form is filled out on site
 and typically carries  three  signatures:  the
engineer's, the installer's, and  the_ regulatory
agency's onsite coordinator's (if appropriate).

In addition,  all  inspection  documents (e.g.,
information on repairs, test sites, etc.)  must  be
carefully maintained. Every repair must be logged
(Figure 7-4). Permits should never be issued to a
facility whose records do not clearly document  all
repairs.

During testing, samples must be identified by seam
number  and  location  along  the seam.   A
geomembrane seam test log is depicted in Figure 7-5.
This log indicates the seam number and length, the
test methods performed, the location and date of the
test, and the person who performed the test.

At the completion of a FML construction, an as-built
record of the landfill construction should be produced
that provides reviewers with an idea of the quality of
work performed in the construction, as well as where
problems  occurred. This record should contain true
panel dimensions, location of repairs, and location of
penetrations.
                                                  103

-------
Dirt within an extruded seam.
                                                            104

-------
 Shear Test
Figure 7-2. Seam strength tests.
                                           Peel Test
                                                                  Owner: _
                                                                   Project:
                                                                  Date/Time:
                  Panel Placement Log
               - Panel Number	---
               	    Weather:	
               	   Temperature:
               	   Wind: 	
                                                                                   -Subgrade Conditions •
                                                                  Line & Grade:
                                                                  Surface Compaction:
                                                                  Protrusions:  	
                                                                  Ponded Water:	
                            Dessication
                                                                                     Panel Conditions
Transport Equipment: 	
Visual Panel Inspection:
Temporary Loading:	
Temp. Welds/Bonds:	
     Temperature:	
Damages:	
                                                                                      Seam Details
                                                                 Seam Nos.:.
                                                                 Seaming Crews:	
                                                                 Seam Crew Testing:.
                                                                 Notes:.
                                                               Figure 7-3. Panel placement log.
                                                           105

-------
                                            Geomembrane Repair Log
Date












Seam












Panels












Location












Material
Type












Description of Damage











|
Type of
Repair










Repair Test
Type




i





1


Tested By,












Figure 7-4. Geomembrane repair log.
                                                    106

-------
                                                Geomembrane Seam Test Log




                                          Continuous Testing             Destructive Test
Seam
No.












Seam
Length












Visual
Inspect












Air
Temp.












Test
Method












Pressure
Init/Final












Peel
Test












Shear
Test












Location












Date












Tested
By
•











Figure 7-5.  Geomembrane seam test log.
                                                       107

-------

-------
                     8.  LINER COMPATIBILITY WITH WASTES
Introduction
This chapter discusses  chemical compatibility
(resistance) of geosynthetic and natural  liner
materials with wastes and leachates.  Even in a
relatively inert  environment, certain materials
deteriorate over  time when exposed  to chemicals
contained in both hazardous and nonhazardous
leachate. It is important to anticipate the kind and
quality of leachate a site will generate and select
liner materials accordingly. The chemical resistance
of any flexible membrane liner (FML) materials,
geonets, geotextiles, and pipe should  be evaluated
before installation.

Chemical compatibility tests using  EPA  Method
9090  should always be performed for hazardous
waste sites, but  some municipal  waste sites also
contain hazardous, nondegradable materials. EPA
conducted a 5-year study of the impact of municipal
refuse on commercially available liner materials and
found no evidence of deterioration within that
period.  However, in a current study of leachate
quality in municipal  landfills, the Agency has
discovered  some organic chemical  .constituents
normally found in hazardous waste landfill facilities.
Apparently small quantities of household hazardous
waste enter municipal sites or  are disposed of as
small quantity generator wastes. As a  result of these
findings, EPA is developing a position on the need for
chemical compatibility tests  for  thousands  of
municipal waste disposal sites.

In general,  cover materials, including membranes
and geosynthetics, do not need to be checked for
chemical compatibility since these materials do not
encounter leachates. Research data indicate that the
predominant gases coming from municipal  sites are
methane, hydrogen, and carbon dioxide, although a
few others may be emitted from household hazardous
 waste. These gases pass through cover materials by
diffusion and evidence to date indicates that they
 have caused no  deterioration of membranes. Also,
 chemical compatibility of cover materials with gases
has not been a major problem at hazardous waste
facilities.

A primary objective of chemical compatibility testing
is to ensure  that liner  materials will remain intact
not just during a landfill's operation but also through
the post-closure period, and preferably longer.  It is
difficult, however, to predict future chemical
impacts. There is no guarantee that liner materials
selected for a site today will be the same as materials
manufactured 20 years from now. For example, the
quality of basic resins  has  improved considerably
over the last few years.

The wastes themselves also change over time. Tests
should be performed to ensure that landfill leachate
will not permeate the liner layer. EPA recommends a
variety of physical property  degradation tests,
including  a fingerprint  program of thermo-
gravimetric analysis,  differential scanning
calorimetric tests,   and  infrared  analysis.
Fingerprinting involves analyzing the molecular
structure of the leachate components. Sometimes a
particularly aggressive leachate component can be
identified by evaluating the fingerprint analysis
tests after exposure of the membrane to the leachate.

Exposure Chamber
The first area of concern in chemical compatibility
testing is the exposure chamber used to hold the
leachate and membranes being tested. The exposure
chamber  tank can be made of  stainless steel,
polyethylene, glass, or a variety of other materials.
Any geosynthetic liner material being considered
must be tested for chemical compatibility with the
leachate. Some leachates have caused rusting and
deterioration of stainless steel tanks in the past, and
if polyethylene is being evaluated, the tank should
be of another type of material to prevent competition
between the tank material and the test specimen for
aggressive agents in the leachate.

The conditions under  which the material is tested
are crucial.  The top of the exposure chamber must be
                                               109

-------
 sealed and the tank should contain no free air space.
 A stirring mechanism in the tank keeps the leachate
 mixture homogeneous and a heater block keeps it at
 an  elevated temperature as required for the  test.
 Stress conditions of the material in the field also
 should be simulated as closely  as possible. The
 original EPA Method 9090 test included a rack to
 hold specimens under stress conditions but was
 revised when some materials shrank in the leachate.
 Due to the hazardous nature of the material, testing
 should be performed in a contained environment and
 safety procedures should be rigorously followed.

 In some cases a sump at the waste management
 facility can be used as an exposure chamber if it is
 large enough. The designer of a new landfill site can
 design a slightly larger sump especially for this
 purpose. However, since the temperature of a sump
 is colder than room temperature (55°F instead of
 72°F),  the geosynthetics  need to  be exposed for a
 longer period of time. Instead of 120 days,  the test
 might take 6 months to a year or longer.

 Representative  Leachate

 It is important that  the sample being, tested is
 representative  of  the  leachate in the landfill.
 Leachate sampled directly from a sump is  usually
 representative, but care must be taken not to mix it
 during removal. This will disturb the  sample's
 homogeneity and may result  in components
 separating out. Another problem  is that municipal
 solid waste landfill  leachate will start to oxidize as
 soon as it leaves the sump  and probably should be
 sampled under an inert atmosphere.

 A sampler should be familiar with the source of all
 the leachate at a site before removing a sample. If
 radioactive materials are present, extra care must be
 taken.

 At  some existing waste management facilities,
 operators have placed coupons of geosynthetic
 materials into sump areas  to monitor  leachate
 effects. Information gathered  from this monitoring
 procedure provides an excellent data base. Regular
 recording of data allows the  operator  to discover
 compatibility problems as they develop, rather than
 waiting until a landfill liner fails. If the  coupon
 shows early signs of deterioration, the operator can
 respond immediately to  potential problems in the
 facility.

When  planning construction of a new site, an
operator first assesses the market to determine the
quantity  and quality of waste the landfill  will
receive. Representative leachate is then formulated
based on the operator's assessment.

The Permit Applicant's Guidance Manual for
Treatment, Storage, and Disposal (TSD) facilities
contains additional  information on  leachate'
representativeness (see Chapter 5, pp. 15-17;
Chapter 6, pp. 18-21; and Chapter 8, pp. 13-16).

Compatibility Testing of Components

Geosynthetics
EPA's Method 9090 can be used to  evaluate all:
geosynthetic materials used in liner and leachate
collection and  removal  systems! currently being
designed. Method 9090 is used to predict the effects
of leachate under field  conditions and  has been
verified with limited field data. The test is performed
by  immersing a geosynthetic  in  a chemical
environment  for  120  days  at two different
temperatures, room and  elevated. Every  30  days,
samples are removed and evaluated for changes in
physical properties. Tests performed on FMLs are
listed in Table 8-1. The results of any test should be
cross-referenced to a second, corollary test to  avoid
errors due to the test itself or to the laboratory
personnel.
                               i
Table 8-1.  Chemical Compatibility Tests for FMLs

             •  Hardness
             •  Melt Index                          ;
             •  Extractives
             •  Volatile Loss
             •  Peel Adhesion
             •  Tear Resistance
             •  Specific Gravity                      ;
             •  Low Temperature
             •  Water Absorption
             •  Puncture Resistance
             •  Dimensional Stability
             •  Modulus of Elasticity
             •  Bonded Seam Strength
             •  Hydrostatic Resistance
             •  Carbon Black Dispersion
             •  Thickness, Length, Width
             •  Tensile at Yield and Break
             •  Environmental Stress Crack
             •  Elongation at Yield and Break
Physical property tests on geotextiles and geonets
must be designed to assess different uses, weights,
and thicknesses  of these  materials, as well as
construction methods used in the field. EPA has a
limited data base on chemical compatibility with
geotextiles. Some tests for geonets and geotextiles
recommended by EPA are listed in Table 8-2. The
ASTM D35  Committee should  be consulted for
information on the latest testing procedures.
                                               110

-------
Table 8-2.  Chemical Compatibility Tests for
          Geonets/Geotextiles
          • Puncture

          • Thickness

          • Permittivity

          • Transmissivity
          • Mass/Unit Area

          • Burst Strength

          • Abrasive Resistant

          • Percent Open Area

          • Ultraviolet Resistivity

          • Grab Tensile/Elongation

          • Equivalent Opening Size

          • Hydrostatic Bursting Strength

          • Tearing Strength (Trapezoidal)

          • Compression Behavior/Crush Strength
Until recently, EPA recommended using 1 1/2 times
the expected overburden pressure for inplane
transmissivity tests. Laboratory research, however,
has revealed that creep and intrusion cause a loss of
transmissivity,  so  the  Agency has amended its
recommendation to 2 to  3 times  the  overburden
pressure. EPA also  recommends that the geotextile
or geonet be aged in leachate, but that the actual test
be performed with water.  Performing the test with
the leachate creates too great a risk of contamination
to test equipment and personnel. The transmissivity
test should be run for a minimum of 100 hours. The
test apparatus should be designed to simulate the
field conditions of the actual cross section as closely
as possible.

Pipes
The crushing strength of pipes also should be tested.
There have been examples where pipes in landfills
have actually collapsed, and thus forced the site to
stop operating. The ASTM  D2412 is used to measure
the strength of pipe materials.

Natural Drainage Materials
Natural drainage materials should be tested to
ensure that they will not dissolve in the leachate or
form a precipitant that might clog the system. ASTM
D2434 will evaluate the ability of the  materials to
retain permeability characteristics, while ASTM
D1883 tests for bearing ratio, or the ability of the
material to support the waste unit.

Blanket Approvals
EPA does not grant  "blanket approvals" for any
landfill construction materials. The  quality of liner
materials  varies  considerably,  depending on
quantities produced and on the manufacturer. Even
high density polyethylene (HOPE) does not receive
blanket approval. The Agency, together with a group
of; chemists,  biologists, and  researchers from the
liner manufacturing industry,  determined that
HDPE varies slightly in its composition among
manufacturers. Because different calendaring aids,
processing aids, or stabilizer packages can change
the overall  characteristics  of  a  product,  each
material should be individually tested.

Landfill  designers should select  materials on the
basis of site-specific conditions, as the composition of
specific  leachates will  vary from  site to  site. A
designer working with the operator determines in
advance of construction what  materials will be most
effective. In recent years, EPA has restricted certain
wastes, including liquids, from land disposal. These
regulations have expanded the number of potential
candidate materials, thus allowing  more flexibility
to landfill designers.

Interpreting Data
When  liner  material test data show the  rate of
change of the material to be nil over a period of time,
then the  membrane is probably not  undergoing any
chemical change. There have  been instances,
however, in which a  material was tested for a year
without change and  then suddenly collapsed.  For
this  reason,  the longer the testing process  can
continue, the more reliable the data will be. When
test data reveal a continuous rate of change, then the
material is reacting with the leachate in some way. If
the data  show an initial continuous rate of change
that  then tapers off, new leachate may need to be
added more often. In any case, the situation should
be studied in more detail.

A designer should consult with experts to interpret
data from chemical compatibility tests. To meet this
need, EPA developed a software  system called
Flexible  Membrane Liner Advisory Expert System
(FLEX) to assist in evaluating test data. FLEX is an
expert system that  is based  on  data from many
chemical  compatibility tests and contains
interpretations from experts in the field.
                                                Ill

-------

-------
 9.  LONG-TERM CONSIDERATIONS: PROBLEM AREAS AND UNKNOWNS
Introduction
This chapter presents an overview of long-term
considerations regarding the liner and collection
systems of hazardous  waste landfills,  surface
impoundments, and waste piles.  Included in the
discussion are flexible membrane liner and clay liner
durability, potential problems in leachate collection
and removal systems, and disturbance and aesthetic
concerns in caps and closures.

In judging the impact of any facility, site-specific
conditions such as geology and stratigraphy;
seismicity; ground-water location and  quality;
population density; facility size; leachate quantity
and quality;  and nontechnical political, social, and
economic factors must be taken into account. Table
9-1 summarizes areas of concern in various landfill
materials and components.

One of the  most important considerations in
planning a waste facility is estimating the length of
time the facility is expected  to operate. Some
recommended time frames for different kinds of
facilities are:

  • Heap leach pads           1-5 years
  • Waste piles               5-10 years
  • Surface impoundments     5-25 years
  • Solid waste landfills        30-100 years
  • Radioactive waste landfills  100-1000+years

None of these time  frames  are  set forth in
regulations, however. The only time frame regulated
by EPA is the 30-year post-closure care period for all
hazardous waste landfill facilities.

Flexible Membrane Liners
The major   long-term consideration  in  any
synthetically lined  facility is the  durability of
flexible membrane liners (FMLs). In  the absence of
sunlight, oxygen, or stresses of any kind, a properly
formulated, compounded, and manufactured FML
will stay intact indefinitely. This is because stable
polymers in isolation have an equilibrium molecular
structure that prevents aging. The usual indicators
of stress are changes in density, p, and  glass
transition temperature, Tg. The  glass transition
temperature is the temperature below which the
amorphous region of a crystalline polymer is rigid
and brittle (glossy) and above which it is rubbery or
fluidlike.

Polymers in the field, however, are subject to  many
external influences and stresses. Experiments done
on FML materials attempt to simulate the long-term
in situ aging processes. One approach is to place a
sample of material in a test chamber at  room
temperature (approximately 70°F), and another
sample in a chamber heated to 120° to 160°F. The
activation energy for the two FMLs is evaluated.
Then a model based on the Arrhenius equation is
used to determine the length of time it would take
the sample kept  at  70°F to degrade to the  same
extent as the high temperature sample.  This
procedure, however, assumes that temperature
increase is physically equivalent to the time of
exposure in the field, an assumption with which
many chemists disagree.

Therefore,  in the absence of a direct measurement
method for FML lifetime, it becomes necessary to
evaluate all of the possible degradation mechanisms
that may contribute to aging.

Degradation Concerns
A number of mechanisms contribute to degradation
in the  field, many of which can be controlled with
proper design  and construction.  A FML can be
weakened by various  individual  physical,
mechanical, and chemical phenomena or by the
synergistic effects of two or  more of these
phenomena. Polymeric materials have an extremely
elongated  molecular structure. Degradation cuts
across the length of this structure in a process known
as chain scission. The more chain breakages that
occur, the more the polymer is degraded by loss of
                                             113

-------
Table 9-1.  Long-Term Concerns In Landfill Mechanisms (Y = yes; N = no)
uap uap - HVVUH LCR

1.
2.
3.
4.
5.
6.
Mechanism
Movement of
Subsoil
Subsidence of
Waste
Aging
Degradation
Clogging
Disturbance
FML
N
Y
Y
Y
N
Y
Clay
N
Y
Y
N
N
Y
Nat.
N
Y
Y
N
Y
Y
SYN
N
Y
Y
Y
Y
Y
P-FML
Y
N
Y
Y
N
N
Nat.
N
N
Y
N
Y
N
SYN
N
N
Y
Y
Y
N
Sec.
FML
Y
N
Y
Y
N
N
Liner
Clay
Y
N
N
N
N
N ;
LDCR
Nat.
N
N
N
N
Y
N
SYN .
N
N
Y
Y
Y
N
where:
  FML  = geomembrane liner
  LCR  » leachate collection and removal system
  SWCR s surface water collection and removal system
  Nat   a made from natural soil materials
  Syn.  - made from synthetic polymeric materials
strength and loss of elongation. Each of the processes
involved in chain scission will be discussed in the
following sections.

Oxidation Degradation
Oxidation is a major source of polymer degradation
leading to a loss  of mechanical  properties and
embrittlement. The steps in this process are as
follows:
  Heat liberates free radicals.
  Oxygen uptake occurs.
  Hydroperoxides accelerate uptake.
  Hydrogen ions attach to tertiary carbons which
  are most vulnerable.
• Subsequent bond scission occurs.

At high temperatures (over 200°F) oxidation occurs
very rapidly.  Consequently,  oxygen  will  create
serious problems for FMLs built near furnaces,
incinerators, or in extremely hot climates. The
impact of oxidation is greatly reduced at ambient
temperatures.

One can minimize oxidative degradation of FMLs by
designing facilities with FMLs buried  to avoid
contact with oxygen and to dissipate heat generated
by direct rays of the sun. Oxygen degradation is a
very serious problem with materials used for surface
impoundments, however, where the FML cannot be
buried or covered.

Ultraviolet Degradation
All polymers degrade when exposed to ultraviolet
light via the process of photooxidation. The  part of
the ultraviolet spectrum responsible for the bulk of
polymer degradation is the wavelength UV-B (315-
380 nm). ASTM D4355 uses Xenon Arc apparatus for
assessing the effects of this wavelength on polymeric
test specimens.  The  Xenon Arc apparatus  is
essentially a weatherometer capable of replicating
the effects of sunlight under laboratory conditions.

Blocking or screening agents, such as carbon black,
are commonly used to retard ultraviolet degradation.
For this reason, FMLs are manufactured with
approximately 2 to 3 percent carbon black. Even that
small amount  effectively retards degradation by
ultraviolet rays. Although the  addition  of carbon
black retards  degradation, it does not  stop it
completely. Ultraviolet degradation, however, can be
prevented by burying the material beneath 6 to 12
inches of soil. FMLs should be buried within 6 to 8
weeks of the time of construction, geonets within 3 to
6 weeks, and geotextiles within 1 to 3 weeks, i.e., the
higher the surface area of the material, the more
rapidly the geosynthetic must be covered.

In surface impoundments where FMLs cannot be
buried,  ultraviolet degradation  also contributes to
the oxidation degradation. An attempt still should be
made to cover the FML, even though sloughing of the
cover soils will occur unless the  site has very gentle
slopes. Various other covering strategies are being
evaluated, such as bonding geotextiles to FML,
surfaces.

High Energy Radiation     '
Radiation is a serious problem,  ajs evidenced by the
Nuclear  Regulatory Commission  and  U.S.
Department of Energy's concerns with transuranic
and high level nuclear wastes. High energy radiation
breaks the molecular chains of polymers and gives
off various products of disintegration.

As of 1992, low-level radioactive wastes, such as
those from hospitals and testing laboratories, must
                                                114

-------
be contained in landfills.  The effects of low-level
radiation associated with these waste materials on
polymers still needs to be evaluated.

Chemical Degradation: pH Effects
All polymers swell to a certain extent when placed in
contact with water (pH = 7) because they accept
water and/or  water vapor into their molecular
structure. Degrees of  swelling for some common
polymers are listed below:
  •  Polyvinyl chloride (PVC)

  •  Polyamide (PA)

  •  Polypropylene (PP)

  •  Polyethylene (PE)

  •  Polyester (PET)
10 percent

4 to 4.5 percent
3 percent

0.5 to 2.0 percent
0.4 to 0.8 percent
Polymer swelling, however, does  not necessarily
prevent a material from functioning properly. The
U.S. Bureau of Reclamation has observed polyvinyl
chloride liners functioning  adequately in water
canals for 20. to 25  years despite relatively large
increases in the thickness of the material.

In very acidic  environments (pH  <  3),  some
polymers, such  as polyamides, (i.e., Kevlar and
nylon) begin to degrade. On the other end of the
spectrum, certain polyesters  degrade  in extremely
alkaline environments  (pH   >   12).  High
temperatures  generally accelerate the chemical
degradation process. Most landfill leachates are not
acidic or basic enough to cause concern. However, in
certain kinds of landfills, such as. those used for ash
disposal, the pH of the leachate might be  quite
alkaline and needs to  be taken into account when
choosing liner materials.

Chemical Degradation:  Leachate
EPA's Method 9090 is a test procedure  used  to
evaluate leachate degradation of FML materials. As
described in Chapter Eight,  the FML must be
immersed in the site-specific  chemical environment
for at least 120 days at two different temperatures.
Physical and mechanical properties of the tested
material are then compared to  those of the  original
material every 30 days. Assessing subtle property
changes can be difficult. Flexible Liner Evaluation
Expert (FLEX), a software system designed  to assist
in the Resource Conservation Recovery Act  (RCRA)
permitting process, can help  in evaluating EPA
Method 9090 test data.

Biological Degradation
Neither laboratory nor field tests have demonstrated
significant evidence  of biological degradation.
Degradation by fungi or bacteria cannot take place
unless the microorganisms attach themselves to the
 polymer and find the end of a molecular chain, an
 extremely unlikely event. Chemical companies have
 been unable to manufacture biological  additives
 capable of destroying  high-molecular weight
 polymers,  like those used in FMLs  and related
 geosynthetic materials. Microbiologists have  tried
 unsuccessfully to make usable biodegradable plastic
 trash bags for many years. The polymers in FMLs
 have 10,000 times the molecular weight of these
 materials, thus are very unlikely to biodegrade from
 microorganisms.

 There also is little evidence that insects or burrowing
 animals destroy polymer liners or cover materials. In
 tests done with rats placed in lined boxes, none of the
 animals were able to chew their way  through the
 FMLs. Thus, degradation  from a wide spectrum of
 biological sources seems highly unlikely.


 Other Degradation Processes
 Other possible sources  of degradation include
 thermal processes, ozone,  extraction via diffusion,
 and delamination. Freeze-thaw cycling,  or the
 process by  which a material undergoes alternating
 rapid extremes  of temperature, has proven to  have
 an insignificant effect on polymer strength or  FML
 seam strength. Polymeric materials experience some
 stress due to warming, thereby  slightly decreasing
 their strength, but within  the range of 0° to 160°F,
 there is no loss of integrity.

 Ozone is related to ultraviolet degradation in the
 photooxidation  process, and, therefore, creates a
 more serious problem for polymeric materials.
 However, ozone effects can be essentially eliminated
 by covering the geosynthetic materials within the
 time frames previously mentioned.

 In  the extraction via  diffusion mechanism,
 plasticizers leach out of polymers leaving a tacky
 substance on the surface of the material. The FML
 becomes less flexible, but  not, apparently, weaker
 nor less durable.

 Delamination of scrim-reinforced material  was a
 problem until 15 years ago when  manufacturers
 began using large polymer calendar presses. The
 presses thoroughly  incorporate  the scrim
 reinforcement, so that delamination rarely occurs
 today.


 Stress-induced Mechanisms
 Freeze-thaw, abrasion, creep, and stress cracking are
all stress mechanisms that can affect polymers. The
first two, freeze-thaw and abrasion, are  not likely to
be problems if the material is buried  sufficiently
deep. Soil  burying will  eliminate temperature
extremes. Abrasion is a consideration only in surface
                                               115

-------
impoundments in which water waves come into
direct contact with the FML.

Creep
Creep refers to the deformation of the FML over a
prolonged period of time under constant stress. It can
occur at side slopes, at anchor trenches, sumps,
protrusions, settlement locations, folds, and creases.

A typical  creep  test for a  FML,  or any  other
geosynthetic material, involves suspending a load
from an 8-inch wide tensile test specimen. Initially
an elastic elongation of the material occurs. The
material should quickly reach an equilibrium state,
however, and experience no further elongation over
time. This is shown in the stabilized lower curve in
Figure 9-1. The second and third curves in Figure 9-1
show test specimens  undergoing states of constant
creep elongation and creep failure, respectively.
        @ o = "x"% oy
                          Creep Failure
                                 Constant Creep
                                 No Creep
                   Time
Figure 9-1.  Typical results of a sustained load (creep) test.
One can use  the design-by-function concept to
minimize creep by selecting materials in which the
allowable  stress compared with the actual stress
gives a high factor of safety.  For semicrystalline
FMLs, such as polyethylenes, the actual stress must
be significantly less than the yield stress. For scrim-
reinforced FMLs  such  as chlorosulfonated
polyethylene  (CSPE), or reinforced ethylene
propylene diene monomer (EPDM), the actual stress
must be significantly less than the breaking strength
of the scrim. Finally, for nonreinforced plastics such
as PVC or nonreinforced chlorinated polyethylene
(CPE), the actual stress must be less than the
allowable stress at  20  percent  elongation. In all
cases,  one should maintain a factor of safety of 3 or
higher on values for these materials.

Stress Cracking
Stress cracking is a potential problem with
semicrystalline FMLs. The higher the crystalline
portion of the molecular structure, the lower the
portion of the amorphous phase and the greater the
possibility of  stress  cracking. High  density
polyethylene (HOPE) is the primary material of
concern.

ASTM defines stress cracking as a brittle failure that
occurs at a stress value less than a material's short-
term strength. The test  usually applied to FMLs is
the "Bent Strip Test," D1693. The bent strip test is a
constant  strain test that depends on the type and
thickness of the material being tested. In performing
the test, a specimen of the FML 0.5 inch wide by 1.5
inches long is  prepared by notching its surface
approximately 10 mils deep. Then the specimen is
bent 180  degrees and placed within the flanges of a
small channel holder  as  shown in Figure 9-2.
Approximately 10 replicate specimens can be placed
in the holder simultaneously. The assembly is then
placed in a glass  tube containing a surface active
wetting agent and kept  in a constant temperature
bath at  122°F. The  notch tips  are observed  for
cracking  and/or crazing. Most specifications call for
stress-crack' free results for 500 or 1,000  hours.
Commercial HDPE sheet usually performs very well
in this particular test.

There are two things, however, that the  D1693 test
does not allow: a constant stress  testing  of the
material  and an evaluation of the seams.  The D1693
process bends the test specimen initially,  but then
allows it to relax into its original state. Furthermore,
the notch cannot be made to span over  separate
sheets at seam locations.

ASTM D2552, "Environmental Stress  Rupture
Under Tensile Load," tests HDPE materials under
constant  stress conditions. In this particular test,
dogbone-shaped specimens under constant load are
immersed in a  surface active agent at  122°F (see
Figure 9-3). The test specimens eventually enter
elastic, plastic, or cracked states.  Commercially
available HDPE sheet material performs very well
in this test, resulting in negligible (=  1 percent)
stress cracking. The test specimens are generally
elastic for stresses less  than 50  percent yield and
plastic for stress levels greater than 50 percent yield.

This apparatus can be readily modified to test HDPE
seams (see  Figure  9-4). Long dogbone-shaped
specimens with a constant-width cross section are
taken from  the  seamed region. The  same test
procedure is followed and the test results should be
the same.  If cracking does occur,  the  cracks go
through  the  fillet portion  of the extrusion fillet-
seamed samples or through the FML sheet material
on either side of the fillet. For other types of seams,
the cracking goes through the parent sheet on one or
the other side of the seamed region. Results on a wide
range of field-collected HDPE seams have shown a
relatively  high incidence of  cracking. This
phenomenon is currently being evaluated with
replicate tests; carefully prepared seams; and
                                                116

-------



r
[
A
i
-1
— *i F r*""
G
C J
-*•
*

*


^r
.- D



B.k
Test Sample





J







,
N
j
^
r
*

)
j
)
J
A
A
^- J


E



**}**'
^J
<^i£j1








L,
'CL.
5i
!*=:
»» —
•^
^~
s
>s^_




.



3 )
^- X— ^
Test
Spec men Holder Assembly
(B) (C)
Figure 9-2. Details of ASTM D1693 on "Environmental Stress-Cracking of Ethylene Plastics."
                         Micro Switch to
                             Timers
                                             Pin
                                 r-3:1 MAn/ Joints

                                          J
                           Shot
                           Can
s
%
CO
76.20 cm
30"
20 Positions


T^
I
h
rn
„• •*•

-Specimen
p=o=-





                                  Side View
                                                • Tray Moved Up and
                                                 Down on Rack and
                                                 Pinion Arrangement
                                                                   Front View
Figure 9-3.  Environmental stress rupture test for HOPE sheet ASTM D2552.
                                                         117

-------
variations of temperature, pressure, and other
seaming controls.
     \

         \
                            O
                                         o
    Front View
Edge View
                                    Edge View
 Figure 9-4. Details of test specimens from ASTM D2552
          modified test for HOPE seams.
The  test  is  sometimes criticized  as being
nonrepresentative of field conditions since the
wetting agent exposes all sides of the seamed region
to liquid, which does  not happen in the field. The
specimen also is too narrow to simulate  real life
wide-width action. Also there is no confinement on
the surfaces of the material. While these criticisms
do challenge the test as being nonrepresentative,
there have been three field failures that mimicked
the laboratory  cracking exactly. The first  was. in a
surface impoundment lined with 80-mil HDPE that
was an extrusion fillet seam. The problem was not
picked up by construction quality assurance work,
but instead occurred after the facility was closed. The
second case involved extensive FML seam failures at
a site in the Southwest. The seam used there was a
flat extrudate.  Cracking originated in several  areas
due to high localized stresses and exposure to wide
temperature fluctuations. The third failure occurred
at a site in the Northeast that used 60 mil HDPE and
a hot wedge seam. In this case a stress crack 18 to 20
inches long formed at the outer track of the wedge.

Of all the  degradation processes reviewed, stress
cracking in field seams is of the greatest current
concern. It appears as though the field problems only
occur in the exposed FML seam areas of surface
impoundments. Work is ongoing to investigate the
phenomenon  further and to  understand the
mechanisms involved. An emphasis on carefully
constructed and monitored field seams will certainly
be part of the final recommendations.
Clay Liners
Clay has a long history of use as a liner material.
Data is available  on the effects of leachate on clay
liners over periods of 10 years or  more, and the
results generally have been satisfactory. While clays
do not experience degradation or stress cracking,
they can have problems with moisture content and
clods. High concentrations of organic solvents, and
severe volume changes and desiccation also cause
concern at specific sites.  The  rapid freezing and
thawing of clay liner materials also  affects their
integrity, but freeze-thaw can usually be alleviated
with proper design and construction considerations.
For  a more  complete  discussion of clay  liner
durability, see Chapter Two.

Leachate Collection and Removal
Systems
The leachate collection and removal system includes
all materials involved in the primary leachate
collection system  and the leak  detection collection
system. For the proper functioning of these systems,
all materials  being used  must be  chemically
resistant to the leachates that they are handling. Of
the natural soil  materials,'gravel and sand are
generally quite resistant to leachates, with the
possible exception of freshly ground limestone. With
this material, a solution  containing calcium,
magnesium, or other ion deposits can develop as the
flow rate decreases in low gradient areas. A form of
weak bonding called "limerock" has been known to
occur. Its occurrence would be disastrous in terms of
leachate collection and  removal.  Regarding
geotextiles and geonets, there are no established test
protocols for chemical resistivity evaluation like the
EPA Method 9090 test for FMLs. Table 9-2 suggests
some tests that should be considered.

Table 9-2. Suggested Test Methods for Assessing Chemical
         Resistance of Geosynthetics Used in Leachate
         Collection Systems (Y = yes; N =  no)
                                  Test Type
                   Geotextile   Geonet   Geocomposite
Thickness
Mass/unit area
Grab tensile
Wide width tensile
Puncture (pin)
Puncture (GBR)
Trapezoidal tear
Burst
Y
Y
Y
Y
N
Y
Y
Y
Y
Y
N
Y
N
Y
N
N
Y
Y
N
N
N
Y
N
N
                             The system for collecting and removing the leachate
                             must function continuously over the anticipated
                             lifetime of the facility and its post-closure care
                             period. During operation, leachate is removed
                             regularly depending on the amount of liquid in  the
                             incoming waste and natural precipitation entering
                                                118

-------
the site.  Leachate,  however, continues to be
generated long after landfill closure. During the first
few post-closure years the rate of leachate removal is
almost 100  percent of that during  construction.
Approximately 2 to 5 years after closure, leachate
generally  levels off to a low-level constant cap leak
rate or, in a very tight, nonleaking closure, falls to
zero (see Figure 9-5).

Clogging is the primary cause of concern for the long-
term performance of leachate collection and removal
systems. Particulate clogging can occur in a number
of locations.  First,  the sand filter itself can clog the
drainage gravel. Second,  the  solid material within
the leachate can clog the  drainage gravel or geonet.
Third, and most likely, the solid suspended material
within.the leachate can clog  the  sand  filter  or
geotextile filter.  The following breakdown  of
particulate concentration in leachate at 18 landfills
shows the  potential for particulate clogging:

  • Total solids               0-59,200 mg/L
  • Total dissolved solids      584 - 44,900 mg/L
  • Total suspended solids     10-700 mg/L
Salts precipitating from high pH leachate,  iron
pcher, sulfides, and carbonates can all contribute to
particulate clogging.

The potential for clogging of a filter or  drainage
system can be evaluated  by modeling the system in
the laboratory. This modeling requires  an  exact
replica system of the proposed components, i.e., cover
soil, geotextile, geonet, etc. Flow rate plotted as a
function of time will decrease in the  beginning, but
eventually should  level off to a horizontal line at a
constant value. It  may take more than 1,000  hours
for this leveling to occur. Zero  slope, at a constant
value, indicates an equlibrium (or nonclogging)
situation.  A continuing negative slope is evidence of
clogging. As yet, there is  no formula or criteria that
can be substituted for this  type of a long-term
laboratory flow test.

Biological clogging can  arise from  many sources
including slime and sheath formation, biomass
formation, ochering,  sulfide deposition, and
carbonate deposition. Ocher is  the precipitate left
when biological activity moves from one zone to
another. It is an iron or sulfide deposit, and is most
likely to occur in  the smallest apertures of filter
materials. Sand filters and geotextile filters are most
likely  to clog,  with  gravel, geonets,  and
geocomposites next in order from most to least likely.

The biological oxygen demand  (BOD) value of the
leachate is a good indicator of biological clogging
potential; the higher the number, the more viable
bacteria are present in the  leachate.  Bacterial
clogging is more likely to be a problem in municipal
landfills than at hazardous waste facilities because
hazardous leachates probably would be fatal to most
bacteria. Currently, an EPA contractor is monitoring
six municipal landfills for evidence of aerobic and
anaerobic clogging. The results should be available
in 1989.

The most  effective method for relieving particulate
and/or biological clogging is creating a high-pressure
water flush to clean out the filter and/or the drain. In
cases of high biological growth, a biocide may also
need to be introduced. Alternatively, a biocide might
be  introduced into the materials during their
manufacture. Geotextiles and geonets can include a
time-release biocide on their surface, or within their
structure. Work  by a number of  geotextile and
geonet manufacturers is currently ongoing in this
area. Measures  to  remedy  clogging  must be
considered in the design stage.

The final factor  to  be considered in  leachate
collection and  removal systems  is  extrusion and
intrusion of materials into the leak detection system.
In a composite primary liner system, clay can readily
extrude through a geotextile into a geonet if the
geotextile has continuous open spaces, i.e., percent
open area (POA) > 1 percent. Therefore, relatively
heavy nonwoven  geotextiles ,are  recommended.
Elasticity and creep can cause geotextiles to intrude
into geonets from composite primary liners as well. A
FML above or below a geonet can also intrude into
the geonet due to  elasticity and creep. Design-by-
function and laboratory evaluations that simulate
field conditions should alert designers to these
potential problems. For all geosynthetics, a high
design ratio value or factor of safety for strength
should be chosen.

Cap/Closure Systems
Water and wind erosion, lack of vegetation, excessive
sunlight, and disturbance by soil-dwelling animals
(or by people) all are potential problems for landfill
closure systems. The effects of rain, hail, snow,
freeze-thaw, and wind are discussed in Chapter Five.
Healthy vegetation growing over the cap minimizes
the erosion of soil on the slopes by these natural
elements.

The effects of animals and of sunlight (ultraviolet
rays and  ozone) can be minimized by adequately
burying the cap/closure facility. Soil depths over
FMLs in covers range from 3 to 6 feet in thickness.
Large rocks above the FML cover can also thwart the
intrusion of animals into the area. Human intrusion,
either accidental  or  intentional,  can  usually be
prevented by posting signs and erecting fences.

The final long-term consideration related to cap and
closure systems  is aesthetic. The New  Jersey
Meadowlands Commission is planning for the final
                                                119

-------
1
•^ 50
CD
Q.
o
s?
n
^^
Conl-iS. j
Weekly 1 Monthly
X^ Cap Leakage
i ' ** ^~~ — __. - * No Leakaae
                                                             To
                                                                     30
                                           Years after Closure

 Figure 9-5. Approximate amount of leachate withdrawal after closure.
closure of 54 landfills in the northeastern part of the
state, all but 3 of which are already closed and ready
to be capped. A graphic artist was hired to design an
attractive landscape  out of one facility along a
heavily traveled automobile  and rail  route. The
design included looping pipes for methane recovery,
a solar lake,  and an  8-foot concrete  sphere all
contributing to a visually pleasing lunar theme.

The performance  of a capped and closed waste
facility is critically important. If a breach  should
occur many years after closure, there is a high
likelihood that maintenance forces would  be
unavailable. In that event, surface water could enter
the facility with largely unknown consequences.
Thus the design stage must be carefully thought out
with long-term considerations in mind.
                                                120

-------
                       10.  LEAK RESPONSE  ACTION  PLANS
This final chapter reviews proposed requirements for
Response Action Plans, or RAPs, that are contained
in the proposed leak detection rule issued in May,
1987. It focuses on the concepts behind the RAPs and
the preliminary, technical calculations used  in
developing them. The main topics of discussion will
be the  technical basis for the two response action
triggers, action leakage  rate (ALR) and rapid and
large leakage (RLL) rate; the RAPs themselves; and
the RAP submittal process.

Background
In the  Hazardous and Solid  Waste Amendments
(HSWA) of 1984, Congress required that leaks from
new land disposal facilities be detected at the earliest
practical time. However, HSWA did not require or
specify actions to be taken once a leak is detected in
the leak detection system. Therefore, EPA proposed
requirements for response action plans to deal with
leaks detected in the leak detection system between
the two liners. EPA realizes that even with a good
construction quality assurance plan, flexible
membrane liners (FMLs) will allow some liquid
transmission either through water vapor permeation
of an intact FML, or through small pinholes or tears
in a slightly flawed FML. Leakage rates resulting
from these mechanisms can range from less than 1 to
300 gallons per acre per  day (gal/acre/day). If
unchecked, these leak rates may result in increased
hydraulic heads acting on the bottom liner and
potential subsequent damage to the liner system.

The idea behind the RAP is to be  prepared for any
leaks or clogging of the  drainage layer in the  leak
detection system that may occur during \ the active
life or post-closure care period of a waste facility. The
first step is to identify the top liner leak rates that
would require response  actions. Therefore, in the
proposed leak detection rule of May 29, 1987, EPA
established two triggers for response  actions: the
Action Leakage Rate (ALR) and the Rapid and Large
Leakage (RLL) rate. The  ALR is a low-level leak rate
that would indicate the presence of a small hole or
defect in the top liner. The RLL is indicative  of a
severe breach or large tear in  the  top  liner. A
different level of responsiveness would be required
for leakage rates  above these two triggers. RAPs
developed by owners or operators may  have more
than two triggers as appropriate to cover the range of
leak rates expected for a landfill unit.  In addition to
triggers, the proposed rule also defines the  elements
of a RAP, gives an example of one, and discusses the
procedures for submitting and reviewing a RAP.

Action Leakage  Rate (ALR)
EPA has  historically used the term de  minimus
leakage when referring to  leaks resulting from
permeation of an  intact FML. Action leakage  rate
(ALR) was developed to distinguish leak rates due to
holes from mere permeation of an intact FML, and to
initiate  early interaction between the owner/oper-
ator of the unit and the Agency. The ALR essentially
defines  top  liner  leakage in a landfill,  and  the
proposed value  is based on  calculated  leak rates
through a 1  to 2 mm hole in a FML subject to  low
hydraulic heads on the order of 1 inch. The proposed
ALR, therefore, is representative of well-designed
and operated landfills, although, as proposed, it
would also apply to surface impoundments and waste
piles.

Because EPA is considering  setting a single ALR
value applicable to landfills, surface impoundments,
and waste piles, the Agency calculated top liner leak
rates for different sizes of holes  and for  different
hydraulic  heads. In addition, EPA compared leak
rates for a FML top liner with that for a composite
top liner, since many  new facilities have double
composite liner systems.  Table 10-1  shows  the
results of these calculations for FML and composite
top liners. Even for FMLs with very small holes (i.e.,
1 to 2 mm in diameter), leak rates can be significant
depending on the  hydraulic head  acting on the top
liner.  The addition  of the compacted  low
permeability soil layer to the FML  significantly
reduces these leak rates to less than 10 gal/acre/day,
even for large hydraulic heads that are common in
surface impoundments. These results  indicate that,
                                               121

-------
at least for deep surface impoundments with large
hydraulic heads, double composite liner systems may
be the key to reducing the leak rates to de minimus
levels that are below the proposed ALR.

Table 10-1. Calculated Leakage Rates through FML and
          Composite Liners (gal/acre/day)
                    FML Alone
                           Hydraulic Head, ft
Leakage Mechanism
Small Hole (1-2 mm)
Standard Hole (1 cm2)
0.1
30
300
1
100
1,000
10
300
3,000
             Composite Liner (good contact)
                            Hydraulic Head, ft

 Leakage Mechanism
0.1
              1
                      10
 Small Hole (1-2 mm)     0.01

 Standard Hole (1 cm2)    0.01
             0.1

             0.2
Source:  U.S. EPA. 1987. Background document on proposed liner
        and leak detection rule. EPA/530-SW-87-015.

EPA's  proposed rule sets the ALR  at 5 to 20
gal/acre/day, a difficult range to achieve with  a
primary FML alone (especially for surface impound-
ments). The proposed rule  also enables the
owner/operator to use a site-specific ALR value that
would  take into  account  meteorological  and
hydrogeological factors, as well as design factors that
might result in leak rates that would frequently
exceed the ALR value. Using these factors, a surface
impoundment  that meets  the  minimum
technological requirements of a FML top liner could
conceivably apply for a site-specific ALR value.

Daily leakage rates through top liners can vary by 10
to 20 percent or more, even in the absence of major
precipitation events. Because of these variations,
EPA may allow the landfill owner/operator to
average daily readings over a 30-day period, as long
as the leakage rate does not  exceed 50 gal/acre/day
on any 1 day. If the average daily leak rate  does not
exceed the ALR, then the  owner/operator does not
have to implement a RAP.

Rapid and Large Leakage (RLL)
The Rapid and Large Leakage (RLL) rate is the high-
level trigger that indicates a serious malfunction  of
system components in the double-lined unit  and that
warrants immediate action. In developing the
proposed rule, EPA defined the RLL as  the
maximum  design leakage rate  that the  leak
detection system can accept. In other words, the RLL
is exceeded when the fluid head is greater  than the
thickness of the secondary leachate collection and
removal system (LCRS) drainage layer. The visible
expression of RLL leakage in surface impoundments
is the creation of bubbles, or "whales," as the FML is
lifted up under the fluid pressure. See Chapter Three
for further discussion of "whales".

Because the RLL is highly dependent on the design
of the leak detection system, EPA's proposed rule
requires that owners/operators calculate their own
site-specific RLL  values.  EPA also proposes to
require that owners/operators submit a RAP  for
leakage rates exceeding that value prior to
beginning operation of a unit. The EPA Regional
Administrator must  approve the  RAP before a
facility can receive wastes.

The following  equations  represent  EPA's
preliminary attempt to define a range of potential
RLL values for a hypothetical leak detection system,
which consists of a 1-foot granular drainage layer
with 1  cm/sec hydraulic conductivity. These
calculations are for two-dimensional rather than
three-dimensional  flow.  In  addition,  the equations
apply to flow from a single defect in the FML, rather
than multiple  defects. Therefore,  results from  this
analysis are only preliminary ones, and the EPA will
develop guidance on calculating RLL values in  the
near future.

RLL values can be calculated using the following
equation:
                               where:
          h =

          h
          Qd

          B
          kd
         10)                  (I)'

hydraulic head
flow  rate entering into  the
drainage layer
width of the drainage layer
hydraulic conductivity of the
drainage layer
slope  of the  drainage  layer
perpendicular to, and in the plane
of, flow toward the collection pipe
                               When the value for h exceeds the thickness of the
                               drainage layer (1 foot in this example), the leakage
                               rate is greater than the RLL value for the unit.

                               In reality, a leak from an isolated source, i.e., a tear
                               or a hole in the FML, results in a discreet zone of
                               saturation as the liquids flow toward the collection
                               pipe  (see Figure  10-1). The appropriate variable
                               representing the width of flow, then, is not really B,
                               the entire width of the drainage layer perpendicular
                               to flow, but b, the width of saturated flow pe'rpen-
                               dicular to the flow direction. If b were  known, the
                               equation could be solved. But to date, the data has
                                                122

-------
not been available to quantify b for all drainage
layers and leakage scenarios.
     Leak
               acre, or in units of m2; N = l/4,000m2. Substituting
               this value into Equation 3:
                                                                 h = 4000q/(bkdtan|3)
                                                             (4)
               Where q is in units of liters/1,000 m2/day  (Ltd),
               Equation 4 can be written as follows:
                                                                 h = 4.6 x 10-8q/(bkdtanj3)
                                                              (5)
                                                     The proposed rule requires leak detection systems to
                                                     have a minimum bottom slope of 2 percent (tang) and
                                                     minimum hydraulic conductivity of 10-2 m/sec (kd).
                                                     Substituting these values into Equation 5:
                                                                 h = 2.3 x 10-4 q/b
                                                              (6)
                            • Leak
                             Flow
                            Direction
                    \	7
 High Edge
(Upgradient)
 Lower Edge
(Downgradient)
             Collector Pipe —'

                Cross Section A - A1

 Figure 10-1. Plan view of a leak detection system with a large
           leak flowing over a width b.
 From Equation 1, one can  make  substitutions for
 variables B and Qd and give values for the other
 variables kd and tang. If N represents the frequency
 of leaks in a well-designed and installed unit, then Q,
 the flow rate in the drainage layer (m3/s) is directly
 related to q, the leakage rate per unit area (m/sec):
             Q = NQ or Q = q/N
          (2)
 Combining Equations 1 and 2 and substituting b for
 B, and q for Q:
             h = q/(Nbkdtanp-)
          (3)
 Equation 3 now can be used to define the leakage
 rate (q) that exceeds  the leak detection system
 capacity. All that is needed are the values for the
 other variables (N, kd, tang). For a well-designed and
 installed unit, the frequency of leaks (N) is 1 hole per
where h is in units of m, q is in units of Ltd, and b is
in units of m. For the purposes of these calculations,
it is assumed  that Ltd is equivalent to about 1
gal/acre/day. The final results were derived by using
three different values  for b (the unknown variable)
and determining what values of q between  100 and
10,000 gal/acre/day (Ltd) result in hydraulic heads
exceeding the 1-foot thickness of the drainage layer
(h).


Table 10-2 shows the  results of these preliminary
calculations. For values of q between 100 and 10,000
gal/acre/day and values of b between 3 and 6 foot, the
hydraulic head exceeds 1 foot when leak rates are in
the range of 2,000 to 10,000 gal/acre/day.  Therefore,
RLL values for leak detection systems consisting of
granular drainage layer are  expected to be in the
range of 2,000 to 10,000 gal/acre/day. Clogging of the
drainage layer would decrease the design capacity of
the leak detection system, and hence the RLL value,
over time. With respect to the variables described
above,  clogging of the drainage layer could be
represented using smaller values for b, the width of
saturated  flow, since clogging  would result in a
reduced width of saturated flow. As shown  in Table
10-2, smaller values  of b  reduce the  minimum
leakage rate, q, needed to generate heads exceeding
the 1-foot thickness. EPA plans to issue guidance on
estimating the effect of clogging on RLL values.
                Table 10-2.  Results of Preliminary Studies Defining Ranges
                           of RLL Values
              Width (b)
                 ft
 Flow (q)
gal/acre/day
                               3.3

                               5.0

                               6.6
                                    1,000 -  2,000

                                    2,000 -  5,000

                                    5,000 - 10,000
                                                   123

-------
 Response Action Plans (RAPs)
 According to the proposed leak detection rule, the
 key elements of a RAP are:

 • General description of unit.
 • Description of waste constituents.
 • Description of all events that may cause leakage.
 • Discussion of factors affecting amounts of leakage
   entering LCRS.

 • Design and operational  mechanisms to  prevent
   leakage of hazardous constituents.
 • Assessment of effectiveness of possible response
   actions.

 In developing a RAP, owners/operators of landfills
 should gather information from Part B of the permit
 application, available operational records, leachate
 analysis results for existing facilities, and the
 construction quality assurance  report.  The
 construction  quality  assurance report is  very
 important because it helps define where potential
 leaks are likely to occur in the unit.

 Sources of Liquids Other than Leachate
 Depending on the  unit design and location, other
 liquids besides leachate could accumulate in the leak
 detection system and result in apparent leak  rates
 that exceed the  ALR  value.  For  example,
 precipitation may pass through a tear in the  FML
 that is located above the waste elevation (e.g. a tear
 in the FML at a pipe penetration point). The liquids
 entering  the  leak detection system under  this
 scenario may not have contacted any wastes and
 hence would not be considered  to-be hazardous
 leachate. In addition, rainwater can become trapped
 in the drainage layer during construction  and
 installation of the leak detection system, but these
 construction waters are typically flushed through
 the system early on in the active life of the facility. In
 the case of a composite top liner, moisture from the
 compacted soil component may be squeezed but over
 time and also contribute to liquids collected in the
 leak detection sump. These sources of nonhazardous
 liquids can add significant quantities of liquids to a
 leak detection system and might result in an  ALR
 being exceeded. Therefore,  these  other sources of
 liquids should also be considered when developing a
 RAP, and steps to verify that certain liquids  are not
 hazardous should be outlined in the plan.

 Ground-water permeation  is one other possible
 source of nonhazardous liquids in the leak detection
 system that can occur when the water table elevation
 is above the bottom of the unit. The ability of ground
 water to enter the leak detection sump, however,
raises serious questions about the integrity of the
bottom liner, which is the backup system in a double-
 lined unit. If ground water is being collected in the
 leak detection system, then hazardous constituents
 could conceivably migrate out of the landfill and into
 the environment when the water table elevation
 drops below the bottom of the unit, e.g., in the case of
 dry weather conditions. As  a result, while ground-
 water permeation is another source of liquids, it is
 not a source that would ordinarily be used  by the
 owner/operator to justify ALR exceedances.

 Preparing and Submitting the RAP
 Response action plans must be developed for two
 basic ranges: (1) leakage rates that exceed the RLL
 and (2) leakage rates that equal or exceed the ALR
 but are less than the RLL. In submitting a RAP, a
 facility owner/operator has two choices. First, the
 owner/operator can submit a plan to EPA before the,
 facility opens that describes all measures to be taken
 for "every possible  leakage scenario. The  major
 drawback to this option is that the RAP may have to
 be modified as specific leak incidents occur, because
 there are several variables that affect the selection of
 suitable response actions. One variable is the time at
 which  the leak occurs. For example, if a leak is
 discovered at the beginning of  operation,  the  best
 response might be to locate and repair the leak, since
 there would be little waste in the unit and the tear or
 hole may be easy to fix. If, however, a leak is
 discovered 6 months before a facility is scheduled to
 close, it would probably make sense to close the unit
 immediately to minimize infiltration. If the
 owner/operator chooses to develop  and submit one
 RAP before the unit begins operation, he or she must
 develop suitable response actions for different leak
 rates and for different stages during the active life
 and post-closure care period of the unit.

 The second choice an owner/operator has is to submit
 the RAP in two phases: one RAP for the first range,
 serious RLL leakage, that would be submitted before
 the start of  operation; and another for the second
 range of leakage rates (exceeding the ALR but less
 than the RLL) that would be submitted after a leak
 has been detected.

 EPA developed three generic  types  of response
 actions that the owner/operator must consider when
 developing a RAP for leakage rates greater than or
 equal to the RLL. The three  responses for very
 serious leakage are straightforward:

• Stop receiving waste and close the unit, or close
  part of the unit.
• Repair the leak or retrofit the top liner.
• Institute operational changes.

These three  response actions also  would apply to
leakage rates less than RLL, although, as moderate
to serious responses, they would apply to leakage
                                               124

-------
rates in the moderate to serious range, i.e., 500 to
2,000  gal/acre/day. For  most  landfills,  500
gal/acre/day leak rates would be considered fairly
serious, even though  they may not exceed the RLL..
In addition, clogging of the leak detection system
could also result in serious leakage scenarios at rates
less than 2,000 gal/acre/day. For lower leak rates just
above the ALR, the best response would be promptly
to increase the liquids removal  frequency  to
minimize  head 'on the bottom liner, analyze the
liquids, and follow up  with progress reports.

Another key step in  developing RAPs  is to set up
leakage bands,  with each  band representing a
specific range of leakage rates that  requires a
specific response or  set of responses.  Table  10-3
shows  an  example of a RAP developed for three
specific leakage bands. The  number and range of
leakage bands should be site-specific and take into
account the type of unit (i.e., surface impoundment,
landfill, waste pile),  unit design,  and operational
factors.

Table 10-3.   Sample RAP for Leakage < RLL

ALR = 20 gal/acre/day and RLL = 2,500 gal/acre/day
Leakage Band
(gal/acre/day)
20
20-250
Generic Response Action
Notify RA and identify sources of liquids.
Increase pumping and analyze liquids in
      250-2,500
sump.

Implement operational changes.
The RAP submittal requirements proposed by EPA
differ for permitted facilities and interim status
facilities. For newly permitted facilities, the RAP for
RLL must be submitted along with Part B of the
permit application.  For existing facilities, the RAP
for RLL must be submitted as a request for permit
modification. Facilities in interim status must
submit RAPs for RLL 120 days prior to the receipt of
waste.

If the RAP for low to moderate leakage (greater than
ALR  but less than RLL) has not been  submitted
before operation, EPA has proposed that it must be
submitted within 90 days of detecting a leak. In any
case,  the EPA  Regional Administrator's approval
would be required before  that  RAP can be
implemented.

Requirements for Reporting a Leak
Once a  leak has  been detected,  the proposed
procedure is similar for both ALR and RLL leakage
scenarios. The  owner/operator would need to notify
the EPA Regional Administrator in writing within 7
days of the date the ALR or RLL was determined to
be exceeded. The RAP should be implemented if it
has been approved (as in the case for RLL leaks), or
submitted within 90 days for approval if not already
submitted. Regardless of whether the RAP for  the
leak incident is approved, the owner/operator would
be required to collect and remove  liquids  from  the
leak detection sump. Examples of the liquids should
be analyzed for leachate quality parameters, as
specified by the  Regional Administrator in an
approved RAP. Both the need for analysis and  the
parameters would be determined by the Regional
Administrator.

In addition  to the leachate  sampling, the EPA
Regional  Administrator  would  also specify a
schedule for follow-up reporting, once  the  ALR or
RLL is exceeded. According to the proposed rule, this
follow-up reporting will  include a discussion of the
response actions taken and the change in leak rates
over  time. The first progress report would be
submitted within 60 days of RAP  implementation,
arid then periodically or annually, thereafter, as
specified in an approved RAP. Additional reporting
would also be required within 45 days of detecting a
significant increase in the leak rate  (an  amount
specified in the RAP). This significant increase in
leak rate indicates a failure in the response actions
taken and, therefore, may require modifications of
the RAP and the implementation of other response
actions. These additional reporting and monitoring
requirements  would be  part of the  RAP
implementation to be  completed  only when  the
resulting leak rate drops below the ALR.

Summary
Although the overall containment system consisting
of two liners  and two  LCRSs may achieve  the
performance objective  of preventing hazardous
constituent migration out of the unit for a period of
about 30 to 50 years, the individual components may
at some point malfunction. Liners may  leak or
LCRS/leak detection systems  may clog during the
active life or post-closure  care period. Therefore,
EPA  has developed and proposed requirements for
early response actions to be taken upon detecting a
malfunction of the top liner or leak detection system.
These requirements, once finalized,  will ensure
maximum protection of human  health and  the
environment.
                                               125

-------

-------
                                        Abbreviations

ALR          = Action Leakage Rate
ASTM        = American Society for Testing and Materials
BOD          = biological oxygen demand
°C            = degrees Centigrade
cm/sec        = centimeters per second
CPE          = chlorinated polyethylene
CQA          = Construction Quality Assurance
CSPE         = chlorylsulfonated polyethylene
D  •           = dielectric constant
DR           = design ratio
DSC          = differential scanning calorimetry
DT           .= destruct tests
EPA          = U.S. Environmental Protection Agency
EPDM        = ethylene propylene diene monomer
°F            = degrees Fahrenheit
FLEX        = Flexible Liner Evaluation Expert
FMC          = flexible membrane caps
FML          = flexible membrane liner
FS           = factor of safety
ft             = feet
ft2           = square foot
ft3           = cubic foot                          ]
gal/acre/day   = gallon per acre per day
HOPE        = high density polyethylene
HELP        = Hydrologic Evaluation Landfill Performance Model
HSWA        = Hazardous and Solid Waste Amendment
LCRS        = leachate collection and removal system
LDCR        = leak detection, collection, and removal
LLDPE       = linear low density polyethylene
Ltd           = liters/1,000 m2/day
m2           = square meters
m2/sec        = square meters per second
min          = minute
mm          = millimeters
MTG         = minimum technology guidance
MTR         = minimum technological requirements
NOT         = nondestruct tests
nm           = nanometer
oz/yd2        = ounces per square yard
PA           = polyamide
POA         = percent open space •
PE           = polyethylene
PE           = professional engineer
PET          = polyester
ph           = hydrogen ion concentration
PI           = plasticity index
PLCR        = primary leachate collection and removal
PP           = polypropylene
psf           = pounds per square foot
psi           = pounds per square inch
PVC          = polyvinyl chloride
RAP          = Response Action Plans
RCRA        = Resource Conservation Recovery Act
RLL          = Rapid and Large Leakage Rate
SLCR        = secondary leachate collection and removal
SWCR        = surface water collection and removal
TGA         = thermogravimetric analysis
TOT          = time of travel
USDA        =  U.S.  Department of Agriculture
                                               127
                                                          *US GOVERNMENT PRINTING OFFICE 1993-750-002/ 80286

-------

-------

-------

-------

-------
&EPA

-------