CHAPTER 4

                          SUBPART D
                       DESIGN CRITERIA


                      TABLE OF CONTENTS


4.1  INTRODUCTION

4.2  PERFORMANCE-BASED DESIGN 40 CFR Section 258.40
     4.2.1     Statement of Regulation
     4.2.2     Applicability
     4.2.3     Technical Considerations
               Demonstration Requirements
               Leachate Characterization
               Assessment of Leakage Through Liners
               Leachate Migration in the Subsurface
               Physical Processes Controlling Contaminant
               Transport in the Subsurface
               Chemical Processes Controlling Contaminant
               Transport in the Subsurface
               Biological Processes Controlling Contaminant
               Transport in the Subsurface
               Leachate Migration Models
               Overview of the Modeling Process
               Model Selection
               Analytical Versus Numerical Models
               Spatial Characteristics of the System
               Steady-State Versus Transient Models
               Boundary and Initial Conditions
               Homogeneous Versus Heterogeneous Aquifer/Soil
               Properties
               Availability of Data
               Summary of Available Models
               The EPA Multimedia Exposure Assessment Model
               (MULTIMED)
               Overview of the Model
               Application of MULTIMED to MSWLF Units

4.3  COMPOSITE LINER AND LEACHATE COLLECTION SYSTEM 40 CFR
     Section 258.40
     4.3.1     Statement of Regulation
     4.3.2     Applicability
     4.3.3     Technical Considerations
               Standard Composite Liner Systems
               Soil Liner
               Thickness
               Lift Thickness
               Bonding Between Lifts
               Placement of Soil Liners on Slopes
               Hydraulic Conductivity
               Soil Properties
               Amended Soils
               Testing
               Soil Liner Construction
               Geomembranes
               Material Types and Thicknesses
               Chemical and Physical Stress Resistance
               Installation
               Leachate Collection Systems
               Grading of Low-Permeability Base
               High-Permeability Drainage Layer
               Soil Drainage Layers
               Geosynthetic Drainage Nets
               Leachate Collection Pipes
               Protection of Leachate Collection Pipes
               Protection of the High-Permeability Drainage
               Layer
               Soil Filter Layers
               Geotextile Filter Layers
               Leachate Removal System
               Other Design Considerations
               Construction Quality Assurance and Quality
               Control
               CQA/CQC Objectives
               Soil Liner Quality Assurance/Quality Control
               Soil Liner Pilot Construction (Test Fill)
               Geomembrane Quality Assurance/Quality Control
               Testing
               Destructive Testing
               Non-Destructive Testing
               Geomembrane Construction Quality Assurance
               Activities
               Leachate Collection System Construction
               Quality Assurance

4.4  RELEVANT POINT OF COMPLIANCE 40 CFR Section 258.40(d)
     4.4.1     Statement of Regulation
     4.4.2     Applicability
     4.4.3     Technical Considerations
               Site Hydrogeology
               Leachate Volume and Physical Characteristics
               Quality, Quantity and Direction of
               Ground-Water Flow
               Ground-Water Receptors
               Alternative Drinking Water Supplies
               Existing Ground-Water Quality
               Public Health, Welfare, Safety
               Practicable Capability of the Owner or
               Operator

4.5  PETITION PROCESS 40 CFR Section 258.40(e)
     4.5.1     Statement of Regulation
     4.5.2     Applicability

4.6  FURTHER INFORMATION
     4.6.1     REFERENCES (Specific to Performance-Based
               Design Assessment and Solute Transport
               Modeling)
     4.6.2     REFERENCES (Specific to Design Criteria)
     4.6.3     Models



4.1  INTRODUCTION

     New MSWLF facilities and lateral expansions of existing
units must comply with either a design standard or a
performance standard for landfill design.  The Federal
Criteria do not require existing units to be retrofitted
with liners.  The design standard requires a composite liner
composed of two feet of soil with a hydraulic conductivity
of no more than 1 x 10-7 cm/sec, overlain by a flexible
membrane liner (FML) and a leachate collection system.  A
performance-based design must demonstrate the capability of
maintaining contaminant concentrations below maximum
contaminant levels (MCLs) at the unit's relevant point of
compliance.  The performance standard has been established
to allow design innovation and consideration of
site-specific conditions; approved States may have adopted
alternative design standards.  Owners/operators are advised
to work closely with State permitting agencies to determine
the applicable design standard.  Owners/operators in
unapproved States may use the petition process (Section
258.40(c)) to allow for use of a performance-based design. 
This process is discussed in Section 4.5.

     The technical considerations discussed in this chapter
are intended to identify the key design features and system
components for the composite liner and leachate collection
system standards, and for the performance standard.  The
technical considerations include 1) design concepts, 2)
design calculations, 3) physical properties, and 4)
construction methods for the following:

1)   Designs Based on the Performance Standard

     *    Leachate characterization and leakage assessment;

     *    Leachate migration in the subsurface;

     *    Leachate migration models; and 

     *    Relevant point of compliance assessment.

2)   Composite Liners and Leachate Collection Systems

     *    Soil liner component (soil properties lab testing,
          design, construction, and quality
          assurance/quality control testing);

     *    Flexible membrane liners (FML properties, design
          installation, and quality assurance/quality
          control testing);

     *    Leachate collection systems (strength and
          compatibility, grading and drainage, clogging
          potential, and filtration); 

     *    Leachate removal systems (pumps, sumps, and
          standpipes); and

     *    Inspections (field observations and field and
          laboratory testing).

     Designs based on the performance standard are described
in Section 4.2.  Requirements for composite liners are
discussed in Section 4.3.  These sections address the
minimum regulatory requirements that should be considered
during the design, construction, and operation of MSWLF
units to ensure that they perform in a manner protective of
human health and the environment.  Additional features or
procedures may be used to demonstrate conformance with the
regulations or to control leachate release and subsequent
effects.  For example, during construction of a new MSWLF
unit, or a lateral expansion of an existing MSWLF unit,
quality control and quality assurance procedures and
documentation may be used to ensure that material properties
and construction methods meet the design specifications that
are intended to achieve the expected level of performance. 
Section 4.4 presents methods to assess ground-water quality
at the relevant point of compliance for performance-based
designs.  Section 4.5 describes the applicability of the
petition process for States wishing to petition to use the
performance standard. 

     
4.2  PERFORMANCE-BASED DESIGN 40 CFR Section 258.40(a)(1)

     4.2.1     Statement of Regulation

     (a) New MSWLF units and lateral expansions shall be
constructed:

     (1) In accordance with a design approved by the
Director of an approved State or as specified in Section
258.40(e) for unapproved States. The design must ensure that
the concentration values listed in Table 1 will not be
exceeded in the uppermost aquifer at the relevant point of
compliance as specified by the Director of an approved State
under paragraph (d) of this section, or 

     (2) (See Statement of Regulation in Section 4.3.1 of
this guidance document for the regulatory language for
composite liner requirements).

     (b) (See Statement of Regulation in Section 4.3.1 of
this guidance document for the regulatory language for
requirements pertaining to composite liner and leachate
collection systems). 

     (c) When approving a design that complies with
paragraph (a)(1) of this section, the Director of an
approved State shall consider at least the following
factors:

     (1) The hydrogeologic characteristics of the facility
and surrounding land;

     (2) The climatic factors of the area; and

     (3) The volume and physical and chemical
characteristics of the leachate.

     (d) (See Statement of Regulation in Section 4.4.1 of
this guidance document for a discussion of the determination
of the relevant point of compliance.)


************************************************************
                           TABLE 1

                (40 CFR 258.40; 56 FR 51022;
                      October 9, 1991)

     Chemical                                MCL(mg/l)

     Arsenic                                 0.05
     Barium                                  1.0
     Benzene                                 0.005
     Cadmium                                 0.01
     Carbon tetrachloride                    0.005
     Chromium (hexavalent)                   0.05
     2,4-Dichlorophenoxy acetic acid         0.1
     1,4-Dichlorobenzene                     0.075
     1,2-Dichloroethane                      0.005
     1,1-Dichloroethylene                    0.007
     Endrin                                  0.0002
     Fluoride                                4.0
     Lindane                                 0.004
     Lead                                    0.05
     Mercury                                 0.002
     Methoxychlor                            0.1
     Nitrate                                 10.0
     Selenium                                0.01
     Silver                                  0.05
     Toxaphene                               0.005
     1,1,1-Trichloroethane                   0.2
     Trichloroethylene                       0.005
     2,4,5-Trichlorophenoxy acetic acid      0.01
     Vinyl Chloride                          0.002
************************************************************
     

     4.2.2     Applicability

     The Director of an approved State may approve a
performance-based design for new MSWLF units and lateral
expansions of existing units (see Section 4.3.2), if it
meets the requirements specified in 40 CFR 258.40(a)(1).  A
performance-based design is an alternative to the design
standard (composite liner with a leachate collection
system).  The composite design is required in unapproved
States; however, if EPA does not promulgate procedures for
State approval by October 9, 1993, the performance-based
design may be available through the petition process (see
Section 4.5).


     4.2.3     Technical Considerations

Demonstration Requirements

     For approval of landfill designs not conforming to the
uniform design standard of a composite liner system and a
leachate collection system (40 CFR Section 258.40(a)(2)),
the owner or operator of the proposed MSWLF unit must
demonstrate to the Director of an approved State that the
design will not allow the compounds listed in Table 1 of
Section 258.40 to exceed the MCLs in ground water at the
relevant point of compliance.  The demonstration should
consider an assessment of leachate quality and quantity,
leachate leakage to the subsurface, and subsurface transport
to the relevant point of compliance.  These factors are
governed by site hydrogeology, waste characteristics, and
climatic conditions.

     The nature of the demonstration is essentially an
assessment of the potential for leachate production and
leakage from the landfill to ground water, and the
anticipated fate and transport of  constituents listed in
Table 1 to the proposed relevant point of compliance at the
facility.  Inherent in this approach is the need to evaluate
whether contaminants in ground water at the relevant point
of compliance will exceed the concentration values listed in
Table 1.  If so, then the owner or operator needs to obtain
sufficient site-specific data to adequately characterize the
existing ground-water quality and the existing ground-water
flow regime (e.g., flow direction, horizontal and vertical
gradients, hydraulic conductivity, stratigraphy, and aquifer
thickness).

     An assessment should be made of the effect MSWLF
facility construction will have on site hydrogeology.  The
assessment should focus on the reduced infiltration over the
landfill area and altered surface water run-off patterns. 
Reduction of ground-water recharge and changes in surface
water patterns resulting from landfill construction may
affect ground-water gradients in some cases and may result
in changes in lateral flow directions.  One example of a
hypothetical performance-based demonstration follows.

     It is possible that a MSWLF unit located in an arid
climatic zone would not produce leachate from sources of
water (e.g., precipitation) other than that existing within
the waste at the time of disposal.  In such an environment,
an owner or operator may demonstrate that significant
quantities of leachate would not be produced.  The
demonstration should be supported by evaluating historic
precipitation and evaporation data and the likelihood that
the unit could be flooded as the result of heavy rains,
surface run-off, or high water tables.  It may be possible,
through operational controls, to avoid exposing waste to
precipitation or infiltration of water through overlying
materials.  If significant leachate production would not be
expected, the regulatory authority, when reviewing the
demonstration, should consider the hydrogeologic
characteristics of the facility and the surrounding area, in
addition to the expected volume of leachate and climatic
factors.

     Assuming leachate is produced, the demonstration should
evaluate whether constituents listed in Table 1 can be
expected to be present at concentrations greater than the
MCLs.  If such a demonstration is possible, it must address
the hydrogeologic characteristics of the facility and the
surrounding land to comply with Section 258.40(d).  The
following sections describe the various parts of a
demonstration in greater detail.


Leachate Characterization

     Leachate characterization should include an assessment
and demonstration of the quantity and composition of
leachate anticipated at the proposed facility.  Discussion
of this assessment follows.

     Estimates of volumetric production rates of leachate
are important in evaluating the fate and transport of the
constituents listed in Table 1.  Leachate production rates
depend on rainfall, run-on, run-off, evapotranspiration,
water table elevation relative to the bottom of the landfill
unit, in-place moisture content of waste, and the prevention
of liquid disposal at the site.  Run-on, run-off, and water
table factors can be managed traditionally through design
and operational controls.  The MSWLF Criteria prohibit bulk
or containerized liquid disposal.  Incident precipitation
and evapotranspiration can be evaluated using models (e.g.,
HELP) or other methods of estimating site-specific leachate
production (e.g., local historical meteorologic data).  

     If leachate composition data that are representative of
the proposed facility are not available, then leachate data
with a similar expected composition should be presented. 
Landfill leachate composition is influenced by:

     (1) The annual infiltration of precipitation and rate
of leaching;

     (2) The type and relative amounts of materials in the
waste stream; and

     (3) The age and the biological maturity of the landfill
unit, which may affect the types of organic and inorganic
acids generated, oxidation/reduction  potential (Eh), and pH
conditions.

     An existing landfill unit in the same region, with
similar waste stream characteristics, may provide
information that will allow the owner or operator to
anticipate leachate composition of the proposed landfill
unit.  A review of existing literature also may be required
to assess anticipated leachate composition if actual data
are unavailable (see U.S. EPA, 1987b).  A wide range of
leachate concentrations are reported in the literature with
higher concentrations of specific constituents typically
reported for the initial leachate from laboratory or field
experimental test fills or test cells.  These "batch"
one-day landfill tests do not account for the long-term
climatic and meteorological influences on a full-scale
landfill operation.  Such high initial concentrations are
not typical of full-scale operations (which are subject to
the dilution effects of incidental rainfall on unused
portions of the unit).


Assessment of Leakage Through Liners

     An assessment of leakage (the volumetric release of
leachate from the proposed performance-based design) should
be based on analytical approaches supported by empirical
data from other existing operational facilities of similar
design, particularly those that have leak detection
monitoring systems (see U.S. EPA, 1990b).  In lieu of the
existence or availability of such information, conservative
analytical assumptions may be used to estimate anticipated
leakage rates.

     The transport of fluids and waste constituents through
geomembranes differs in principle from transport through
soil liner materials.  The dominant mode of leachate
transport through liner components is flow through holes and
penetrations of the geomembrane, and Darcian flow through
soil components.  Transport through geomembranes where
tears, punctures, imperfections, or seam failures are not
involved is dominated by molecular diffusion.  Diffusion
occurs in response to a concentration gradient and is
governed by Fick's first law.  Diffusion rates through
geomembranes are very low in comparison to hydraulic flow
rates in soil liners, including compacted clays.  For
synthetic liners, the most significant factor influencing
liner performance is penetration of the liner, including
imperfect seams or pinholes caused by construction defects
in the geomembrane (U.S. EPA, 1989).

     A relatively new product now being used in liner
systems is the geosynthetic clay liner (GCL).  GCLs consist
of a layer of pure bentonite clay backed by one or two
geotextiles.  GCLs exhibit properties of both soil liners
and geomembranes, and have successfully substituted for the
soil component in composite liner designs.  GCLs are
believed to transport fluids primarily through diffusion
according to their low hydraulic conductivities (i.e., 1 x
10-9 cm/sec reported by manufacturers).  Applications for
GCLs are discussed further in the sections that follow.

     Several researchers have studied the flow of fluids
through imperfections in single geomembrane and composite
liner systems.  Further discussion of liner leakage rates
can be found in Section 4.3.3 below.  For empirical data and
analytical methods the reader is referred to Jayawickrama et
al. (1988), Kastman (1984), Haxo (1983), Haxo et al. (1984),
Radian (1987), Giroud and Bonaparte (1989, Parts I and II),
and Giroud et al. (1989).  Leakage assessments also may be
conducted with the use of the HELP model (U.S. EPA, 1988). 
Version 3.0 of the model is under revision and will include
an updated method to assess leakage that is based on recent
research and data compiled by Giroud and Bonaparte.  


Leachate Migration in the Subsurface

     Leachate that escapes from a landfill unit may migrate
through the unsaturated zone and eventually reach the
uppermost aquifer.  In some instances, however, the water
table may be located above the base of the landfill unit, so
that only saturated flow and transport from the landfill
unit need to be considered.  Once leachate reaches the water
table, contaminants may be transported through the saturated
zone to a point of discharge (i.e., a pumping well, a
stream, a lake, etc.).

     The migration of leachate in the subsurface depends on
factors such as the volume of the liquid component of the
waste, the chemical and physical properties of the leachate
constituents, the loading rate, climate, and the chemical
and physical properties of the subsurface (saturated and
unsaturated zones).  A number of physical, chemical, and
biological processes also may influence migration.  Complex
interactions between these processes may result in specific
contaminants being transported through the subsurface at
different rates.  Certain processes result in the
attenuation and degradation of contaminants.  The degree of
attenuation is dependent on the time that the contaminant is
in contact with the subsurface material, the physical and
chemical characteristics of the subsurface material, the
distance that the contaminant has traveled, and the volume
and characteristics of the leachate.  Some of the key
processes affecting leachate migration are discussed briefly
here.  The information is based on a summary in Travers and
Sharp-Hansen (1991), who in turn relied largely on Aller et
al. (1987), Keely (1987), Keely (1989), Lu et al. (1985),
and U.S. EPA (1988a).


     Physical Processes Controlling Contaminant Transport in
     the Subsurface

     Physical processes that control the transport of
contaminants in the subsurface include advection, mixing and
dilution as a result of dispersion and diffusion, mechanical
filtration, physical sorption, multi-phase fluid flow, and
fracture flow.  These processes, in turn, are affected by
hydrogeologic characteristics, such as hydraulic
conductivity and porosity, and by chemical processes.  

     Advection is the process by which solute contaminants
are transported by the overall motion of flowing ground
water.  A non-reactive solute will be transported at the
same rate and in the same direction as ground water flow
(Freeze and Cherry, 1979).  Advective transport is chiefly a
function of the subsurface hydraulic conductivity
distribution, porosity, and hydraulic gradients.

     Hydrodynamic dispersion is a non-steady, irreversible
mixing process by which a contaminant plume spreads as it is
transported through the subsurface.  Dispersion results from
the effects of two components operating at the microscopic
level: mechanical dispersion and molecular diffusion. 
Mechanical dispersion results from variations in pore
velocities within the soil or aquifer and may be more
significant than molecular diffusion in environments where
the flow rates are moderate to high.  Molecular diffusion
occurs as a result of contaminant concentration gradients;
chemicals move from high concentrations to low
concentrations.  At very slow ground-water velocities, as
occur in clays and silts, diffusion can be an important
transport mechanism.

     Mechanical filtration removes from ground water
contaminants that are larger than the pore spaces of the
soil.  Thus, the effects of mechanical filtration increase
with decreasing pore size within a medium.  Filtration
occurs over a wide range of particle sizes.  The retention
of larger particles may effectively reduce the permeability
of the soil or aquifer.

     Physical sorption is a function of Van der Waals
forces, and the hydrodynamic and electrokinetic properties
of soil particles. Sorption is the process by which
contaminants are removed from solution in ground water and
adhere or cling to a solid surface.  The distribution of a
contaminant between the solution and the solid phase is
called partitioning.   

     Multiphase fluid flow occurs because many solvents and
oils are highly insoluble in water and may migrate in the
subsurface as a separate liquid phase.  If the viscosity and
density of a fluid differ from that of water, the fluid may
flow at a different rate and direction than the ground
water.  If the fluid is more dense than water it may reach
the bottom of the aquifer (top of an aquitard) and alter its
flow direction to conform to the shape and slope of the
aquitard surface.

     Hydraulic conductivity is a measure of the ability of
geologic media to transmit fluids (USGS, 1987).  It is a
function of the size and arrangement of water-transmitting
openings (pores and fractures) in the media and of the
characteristics of the fluids (density, viscosity, etc.). 
Spatial variations in hydraulic conductivity are referred to
as heterogeneities.  A variation in hydraulic conductivity
with the direction of measurement is referred to as
anisotropy.

     Variable hydraulic conductivity of the geologic
formation may cause ground-water flow velocities to vary
spatially. Variations in the rate of advection may result in
non-uniform plume spreading.  The changes in aquifer
properties that lead to this variability in hydraulic
conductivity may be three-dimensional.  If the geologic
medium is relatively homogeneous, it may be appropriate, in
some instances, to assume that the aquifer properties also
are homogeneous.

     Secondary porosity in rock may be caused by the
dissolution of rock or by regional fracturing; in soils,
secondary porosity may be caused by desiccation cracks or
fissures. Fractures or macropores respond quickly to
rainfall events and other fluid inputs and can transmit
water rapidly along unexpected pathways.  Secondary porosity
can result in localized high concentrations of contaminants
at significant distances from the facility.  The relative
importance of secondary porosity to hydraulic conductivity
of the subsurface depends on the ratio of fracture hydraulic
conductivity to intergranular hydraulic conductivity
(Kincaid et al., 1984a).  For scenarios in which fracture
flow is dominant, the relationships used to describe porous
flow (Darcy's Law) do not apply.


     Chemical Processes Controlling Contaminant Transport in
     the Subsurface

     Chemical processes that are important in controlling
subsurface transport include precipitation/dissolution,
chemical sorption, redox reactions, hydrolysis, ion
exchange, and complexation.  In general, these processes,
except for hydrolysis, are reversible.  The reversible
processes tend to retard transport, but do not permanently
remove a contaminant from the system.  Sorption and
precipitation are generally the dominant mechanisms
retarding contaminant transport in the saturated zone.

     Precipitation/dissolution reactions can control
contaminant concentration levels.  The solubility of a solid
controls the equilibrium state of a chemical.  When the
soluble concentration of a contaminant in leachate is higher
than that of the equilibrium state, precipitation occurs. 
When the soluble concentration is lower than the equilibrium
value, the contaminant exists in solution.  The
precipitation of a dissolved substance may be initiated by
changes in pressure, temperature, pH, concentration, or
redox potential (Aller et al., 1987).  Precipitation of
contaminants in the pore space of an aquifer can decrease
aquifer porosity.  Precipitation and dissolution reactions
are especially important processes for trace metal migration
in soils.

     Chemical adsorption/desorption is the most common
mechanism affecting contaminant migration in soils.  Solutes
become attached to the solid phase by means of adsorption. 
Like precipitation/dissolution, adsorption/desorption is a
reversible process.  However, adsorption/desorption
generally occurs at a relatively rapid rate compared to
precipitation reactions.

     The dominant mechanism of organic sorption is the
hydrophobic attraction between a chemical and natural
organic matter that exists in some aquifers.  The organic
carbon content of the porous medium, and the solubility of
the contaminant, are important factors for this type of
sorption.

     There is a direct relationship between the quantity of
a substance sorbed on a particle surface and the quantity of
the substance suspended in solution. Predictions about the
sorption of contaminants often make use of sorption
isotherms, which relate the amount of contaminant in
solution to the amount adsorbed to the solids.  For organic
contaminants, these isotherms are usually assumed to be
linear and the reaction is assumed to be instantaneous and
reversible.  The linear equilibrium approach to sorption may
not be adequate for all situations.

     Oxidation and reduction (redox) reactions involve the
transfer of electrons and occur when the redox potential in
leachate is different from that of the soil or aquifer
environment.  Redox reactions are important processes for
inorganic compounds and metallic elements.  Together with
pH, redox reactions affect the solubility, complexing
capacity, and sorptive behavior of constituents, and thus
control the presence and mobility of many substances in
water.  Microorganisms are responsible for a large
proportion of redox reactions that occur in ground water. 
The redox state of an aquifer, and the identity and quantity
of redox-active reactants, are difficult to determine. 

     Hydrolysis is the chemical breakdown of carbon bonds in
organic substances by water and its ionic species H^+ and
OH_-.  Hydrolysis is dependent on pH and Eh and is most
significant at high temperatures, low pH, and low redox
potential.  For many biodegradable contaminants, hydrolysis
is slow compared to biodegradation.

     Ion exchange originates primarily from exchange sites
on layered silicate clays and organic matter that have a
permanent negative charge.  Cation exchange balances
negative charges in order to maintain neutrality.  The
capacity of soils to exchange cations is called the cation
exchange capacity (CEC).  CEC is affected by the type and
quantity of clay mineral present, the amount of organic
matter present, and the pH of the soil.  Major cations in
leachate (Ca, Mg, K, Na) usually dominate the CEC sites,
resulting in little attenuation in soils of trace metals in
the leachate. 

     A smaller ion exchange effect for anions is associated
with hydrous oxides.  Soils typically have more negatively
charged clay particles than positively charged hydrous
oxides.  Therefore, the transport of cations is attenuated
more than the transport of anions.

     Complexation involves reactions of metal ions with
inorganic anions or organic ligands.  The metal and the
ligand bind together to form a new soluble species called a
complex.  Complexation can either increase the concentration
of a constituent in solution by forming soluble complex ions
or decrease the concentration by forming a soluble ion
complex with a solid.  It is often difficult to distinguish
among sorption, solid-liquid complexation, and ion exchange. 
Therefore, these processes are usually grouped together as
one mechanism.


     Biological Processes Controlling Contaminant Transport
     in the Subsurface

     Biodegradation of contaminants may result from the
enzyme-catalyzed transformation of organic compounds by
microbes.  Contaminants can be degraded to harmless
byproducts or to more mobile and/or toxic products through
one or more of several biological processes.  Biodegradation
of a compound depends on environmental factors such as redox
potential, dissolved oxygen concentration, pH, temperature,
presence of other compounds and nutrients, salinity, depth
below land surface, competition among different types of
organisms, and concentrations of compounds and organisms. 
The transformations that occur in a subsurface system are
difficult to predict because of the complexity of the
chemical and biological reactions that may occur. 
Quantitative predictions of the fate of biologically
reactive substances are subject to a high degree of
uncertainty, in part, because little information is
available on biodegradation rates in soil systems or ground
water.  First-order decay constants are often used instead.  

     The operation of Subtitle D facilities can introduce
bacteria and viruses into the subsurface.  The fate and
transport of bacteria and viruses in the subsurface is an
important consideration in the evaluation of the effects of
MSWLF units on human health and the environment.  A large
number of biological, chemical, and physical processes are
known to influence virus and bacterial survival and
transport in the subsurface.  Unfortunately, knowledge of
the processes and the available data are insufficient to
develop models that can simulate a wide variety of
site-specific conditions.  

     
Leachate Migration Models

     After reviewing the hydrogeologic characteristics of
the site, the nature of liner leakage, and the leachate
characteristics, it may be appropriate to use a mathematical
model to simulate the expected fate and transport of the
constituents listed in Table 1 to the relevant point of
compliance.  Solute transport and ground-water modeling
efforts should be conducted by a qualified ground-water
scientist (see Section 5.5).  It is necessary to consider
several factors when selecting and applying a model to a
site.  Travers and Sharp-Hansen (1991) provide a thorough
review of these issues. The text provided below is a summary
of their review.



Overview of the Modeling Process

     A number of factors can influence leachate migration
from MSWLF units.  These include, but are not limited to,
climatic effects, the hydrogeologic setting, and the nature
of the disposed waste.  Each facility is different, and no
one generic model will be appropriate in all situations.  To
develop a model for a site, the modeling needs and the
objectives of the study should be determined first.  Next,
it will be necessary to collect data to characterize the
hydrological, geological, chemical, and biological
conditions of the system.  These data are used to assist in
the development of a conceptual model of the system,
including spatial and temporal characteristics and boundary
conditions.  The conceptual model and data are then used to
select a mathematical model that accurately represents the
conceptual model.  The model selected should have been
tested and evaluated by qualified investigators, should
adequately simulate the significant processes present in the
actual system, and should be consistent with the complexity
of the study area, amount of available data, and objectives
of the study. 

     First, an evaluation of the need for modeling should be
made (Figure 4-1).  When selecting a model to evaluate the
potential for soil and ground-water contamination (Boutwell
et al., 1986), three basic determinations must be made
(Figure 4-2).  Not all studies require the use of a
mathematical model.  This decision should be made at the
beginning of the study, since modeling may require a
substantial amount of resources and effort.  Next, the level
of model complexity required for a specific study should be
determined (Figure 4-3).  Boutwell et al. (1986) classify
models as Level I (simple/analytical) and Level II
(complex/numerical) models.  A flowchart for determining the
level of model complexity required is shown in Figure   4-3. 
Finally, the model capabilities necessary to represent a
particular system should be considered (Figure 4-4). 
Several models may be equally suitable for a particular
study.  In some cases, it may be necessary to link or couple
two or more computer models to accurately represent the
processes at the site.  In the section that follows,
specific issues that should be considered when developing a
scenario and selecting a model are described.


************************************************************
                         FIGURE 4-1

          Three Basic Decisions in Model Selection
                          [Graphic]
************************************************************


************************************************************
                         FIGURE 4-2

       Flow Chart to Determine if Modeling is Required
                          [Graphic]
************************************************************


************************************************************
                         FIGURE 4-3

        Flow Chart to Determine the Level of Modeling
          Required for Soil and Groundwater Systems
                          [Graphic]
************************************************************


************************************************************
                         FIGURE 4-4

       Flow Chart for Required Model Capabilities for
                Soil and Groundwater Systems
                          [Graphic]
************************************************************


     Models are a simplified representation of the real
system, and as such, cannot fully reproduce or predict all
site characteristics.  Errors are introduced as a result of:
1) simplifying assumptions; 2) a lack of data; 3)
uncertainty in existing data; 4) a poor understanding of the
processes influencing the fate and transport of
contaminants; and 5) limitations of the model itself. 
Therefore, model results should be interpreted as estimates
of ground-water flow and contaminant transport.  Bond and
Hwang (1988) recommend that models be used for comparing
various scenarios, since all scenarios would be subject to
the same limitations and simplifications.  

     The quality of model results can depend to a large
extent on the experience and judgement of the modeler, and
on the quality of the data used to develop model input.  The
process of applying the model may highlight data
deficiencies that may require additional data collection. 
The model results should be calibrated to obtain the best
fit to the observed data.  The accuracy of the results
obtained from modeling efforts should then be validated. 
Model validation, which is the comparison of model results
with experimental data or environmental data, is a critical
aspect of model application, and is particularly important
for site-specific evaluations. 

     Several recent reports present detailed discussions of
the issues associated with model selection, application, and
validation.  Donigian and Rao (1990) address each of these
issues, and present several options for developing a
framework for model validation.  EPA's Exposure Assessment
Group has developed suggested recommendations and guidance
on model validation (Versar Inc., 1987).  A recent report by
the National Research Council (1990) discusses the issues
related to model application and validation, and provides
recommendations for the proper use of ground-water models. 
Weaver et al. (1989) discuss options for selection and field
validation of mathematical models.  

     
Model Selection

     Ground-water flow and solute transport models range
from simple, analytical calculations to sophisticated
computer programs that use numerical solutions to solve
mathematical equations describing flow and transport.  A
sophisticated model may not yield an exact estimate of water
quality at the relevant point of compliance for a given set
of site conditions, but it may allow an estimate of the
effects of complex physical and chemical processes. 
Depending on the complexity of site conditions and the
appropriateness of the simplifying assumptions, a fairly
sophisticated numerical model may provide useful estimates
of water quality at the relevant point of compliance.

     The following considerations should be addressed when
selecting a model.


     Analytical Versus Numerical Models

     Mathematical models use either analytical,
semi-analytical, or numerical solutions for ground-water
flow and transport equations.  Each technique has advantages
and disadvantages.  Analytical solutions are computationally
more efficient than numerical simulations and are more
conducive to uncertainty analysis (i.e., Monte Carlo
techniques).  Typically, input data for analytical models
are simple and do not require detailed familiarity with the
computer model or extensive modeling experience.  Analytical
solutions are typically used when data necessary for
characterization of the site are sparse and simplifying
assumptions are appropriate (Javandel et al., 1984).  The
limited data available in most field situations may not
justify the use of a detailed numerical model; in some
cases, results from simple analytical models may be
appropriate (Huyakorn et al., 1986).  Analytical models
require simplifying assumptions about the system. 
Therefore, complex interactions involving several fate and
transport processes cannot be addressed in detail. 
Analytical models generally require a limited number of
parameters that are often assumed to be constant in space
and time (van der Heijde and Beljin, 1988).

     Semi-analytical models approximate complex analytical
solutions using numerical techniques (van der Heijde and
Beljin, 1988).  Semi-analytical methods allow for more
complex site conditions than those that can be simulated
with a purely analytical solution.  Semi-analytical solution
methods can consider multiple sources or recharging and
discharging wells.  However, they still require simplifying
assumptions about the dimensionality and homogeneity of the
system.

     Numerical models are able to evaluate more complex site
conditions than either analytical or semi-analytical models. 
Numerical models provide the user with a large amount of
flexibility; irregular boundaries and spatial and temporal
variations in the system can be considered.  Numerical
models require significantly more data than analytical
models, and are typically more computationally intensive. 
Use of a numerical model requires an experienced modeler,
and can involve a larger amount of computer time than
simulations using an analytical or semi-analytical method.

     To select an appropriate model, the complexity of the
site hydrology and the availability of data should be
considered.  If data are insufficient, a highly
sophisticated and complex model should not be used.  In some
situations, it is beneficial to use an analytical or
semi-analytical model as a "screening level" model to define
the range of possible values, and to use a numerical model
when there are sufficient data.  

     A highly complex hydrogeologic system cannot be
accurately represented with a simple analytical model. 
Heterogeneous or anisotropic aquifer properties, multiple
aquifers, and complicated boundary conditions can be
simulated using numerical models.  In addition,
sophisticated numerical models are available that can
simulate processes such as fracture flow.  Because each site
is unique, the modeler should determine which conditions and
processes are important at a specific site, and then select
a suitable model. 


     Spatial Characteristics of the System

     Although actual landfill units and hydrogeologic
systems are three-dimensional, it is often desirable to
reduce the number of dimensions simulated in a mathematical
model to one or two.  Two- and three-dimensional models are
generally more complex and computationally expensive than
one-dimensional models, and therefore require more data.  In
some instances, a one-dimensional model may adequately
represent the system; the available data may not warrant the
use of a multi-dimensional model.  However, modeling a truly
three-dimensional system using a two-dimensional model may
produce results without adequate spatial detail. The choice
of the number of dimensions in the model should be made for
a specific site, based on the complexity of the site and the
availability of data.


     Steady-State Versus Transient Models

     Models can simulate either steady-state or transient
flow conditions.  It may be appropriate to assume that some
ground-water flow systems have reached approximate
"steady-state" conditions, which implies that the system has
reached equilibrium and no significant changes are occurring
over time.  The assumption of steady-state conditions
generally simplifies the mathematical equations used to
describe flow processes, and reduces the amount of input
data required.  

     However, assuming steady-state conditions in a system
that exhibits transient behavior may produce inaccurate
results.  For example, climatic variables, such as
precipitation, vary over time and may have strong seasonal
components.  In such settings, the assumption of constant
recharge of the ground-water system would be incorrect. 
Steady-state models also may not be appropriate for
evaluating the transport of chemicals which sorb or
transform significantly (Mulkey et al., 1989).  The choice
of simulating steady-state or transient conditions should be
based on the degree of temporal variability in the system.


     Boundary and Initial Conditions

     The solution of differential equations describing flow
and transport processes requires that initial and boundary
conditions be specified.  The initial conditions describe
the conditions present in the system at the beginning of the
simulation.  In many ground-water flow and transport models,
these conditions are related to the initial hydraulic
conditions in the aquifer and the initial concentration of
contaminants.  Boundary conditions define the conditions
present on the borders of the system, which may be
steady-state or temporally variable.  The initial and
boundary conditions chosen to represent a site can
significantly affect the results of the simulation. 

     One of the most significant boundary conditions in
solute transport models is the introduction of a contaminant
to the system.  A source of ground-water contamination
should be described in terms of its spatial, chemical, and
physical characteristics, and its temporal behavior. 
Spatially, a source may be classified as a point source,
line source, a distributed source of limited areal or
three-dimensional extent, or as a non-point source of
unlimited extent (van der Hjeide et al., 1988).  Typically,
temporal descriptions of the source term boundary conditions
for models with analytical solutions are constant, constant
pulse, and/or exponential decay (Mulkey et al., 1989). 
Numerical models typically handle a much wider range of
source boundary conditions, allowing for a wide range of
contaminant loading scenarios.


     Homogeneous Versus Heterogeneous Aquifer/Soil
     Properties

     The extent of the spatial variability of the properties
of each aquifer will significantly affect the selection of a
mathematical model.  Many models assume uniform aquifer
properties, which simplifies the governing equations and
improves computational efficiency.  For example, a constant
value of hydraulic conductivity may be assumed at every
point in the aquifer.  However, this assumption may ignore
the heterogeneity in the hydrogeologic system.  Bond and
Hwang (1988) present guidelines for determining whether the
assumption of uniform aquifer properties is justified at a
particular site.  They state that the error associated with
using an average value versus a spatial distribution is
site-specific and extremely difficult to determine.  

     When site-specific data are limited, it is common to
assume homogeneous and isotropic aquifer properties, and to
develop a "reasonable worst-case" scenario for contaminant
migration in the subsurface.  However, as Auerbach (1984)
points out, the assumption of homogeneous and isotropic
aquifers often will not provide a "worst-case" scenario. 
For example, a continuous zone of higher hydraulic
conductivity in the direction of ground-water flow can
result in much higher rates of contaminant movement than
would be predicted in a completely homogeneous aquifer.  To
develop a true "worst-case" model, information on the
probable heterogeneity and anisotropy of the site should be
collected.

     The number of aquifers in the hydrogeologic system also
will affect the selection of a mathematical model.  Some
systems include only a single unconfined or confined
aquifer, which is hydraulically isolated from the
surrounding layers.  Some mathematical models, and in
particular those with analytical solutions, can simulate
only single layers.  In other cases, the upper aquifer may
be hydraulically connected to underlying aquifers.  The
MSWLF Criteria specify that MCLs not be exceeded at the
relevant point of compliance within the uppermost aquifer. 
The uppermost aquifer includes not only the aquifer that is
nearest the ground surface, but also all lower aquifers that
are hydraulically connected to the uppermost aquifer within
the vicinity of the facility.  


     Availability of Data

     Although computer models can be used to make
predictions about leachate generation and migration, these
predictions are highly dependent on the quantity and quality
of the available data.  One of the most common limitations
to modeling is insufficient data.  Uncertainty in model
predictions results from the inability to characterize a
site in terms of the boundary conditions or the key
parameters describing the significant flow and transport
processes (National Research Council, 1990).  The
application of a mathematical model to a site typically
requires a large amount of data.  Inexperienced modelers may
attempt to apply a model with insufficient data and, as a
result, produce model results that are inconclusive.  

     To obtain accurate model results, it is essential to
use data that are appropriate for the particular site being
modeled.  Models that include generic parameters, based on
average values for similar sites, can be used to provide
initial guidance and general information about the behavior
of a system, but it is inappropriate to apply generic
parameters to a specific hydrogeologic system.  An excellent
summary of the data required to model saturated and
unsaturated flow, surface water flow, and solute transport
is presented in Mercer et al. (1983).  This report provides
definitions and possible ranges of values for source terms,
dependent variables, boundary conditions, and initial
conditions.


Summary of Available Models

     Several detailed reviews of ground-water models are
available in the literature.  A number of ground-water
models, including saturated flow, solute transport, heat
transport, fracture flow, and multiphase flow models, are
summarized in van der Heijde et al. (1988).  A report by van
der Heijde and Beljin (1988) provides detailed descriptions
of 64 ground-water flow and solute transport models that
were selected for use in determining wellhead protection
areas.  A review of ground-water flow and transport models
for the unsaturated zone is presented in Oster (1982).  A
large number of ground-water flow and transport models are
summarized by Bond and Hwang (1988).  Finally, Travers and
Sharp-Hansen (1991) summarize models that may be applicable
to problems of leachate generation and migration from MSWLF
units.  (See References supplied in Section 4.6.)

     Table 4-1 (adapted from Travers and Sharp-Hansen
(1991)) provides information on select leachate generation
models.  Tables 4-1a, b, and c list some of the available
models that can be used to predict contaminant transport. 
The factors used to select these models include
availability, documentation, uniqueness, and the size of the
user community.  These models are categorized by the
techniques used to solve flow and transport equations. 
Table 4-1a lists analytical and semi-analytical models, and
Tables 4-1b and 4-1c list numerical models that are solved
by the finite-difference and the finite-element method,
respectively.


************************************************************
                          TABLE 4-1

   Models for Application to Leachate Generation Problems
************************************************************


************************************************************
                         TABLE 4-1a

    Analytical and Semi-Analytical Models for Application
               to Leachate Migration Problems
************************************************************


************************************************************
                         TABLE 4-1b

        Finite-Difference Models for Application to 
                 Leachate Migration Problems
************************************************************


************************************************************
                         TABLE 4-1c

          Finite-Element Models for Application to
                 Leachate Migration Problems
************************************************************


     The types of models that are available for application
to the evaluation of MSWLF designs include leachate
generation models and saturated and unsaturated zone flow
and transport models.  The level of sophistication of each
of these types of models is based on the complexity of the
processes being modeled.  The majority of the models
consider flow and transport based on advection dispersion
equations.  More complex models consider physical and
chemical transformation processes, fracture flow, and
multiphase fluid flow.

     Leachate generation models predict the quantity and
characteristics of leachate that is released from the bottom
of a landfill.  These models are used to estimate
contaminant source terms and the releases of contaminants to
the subsurface.  Flow and transport models simulate the
transport of contaminants released from the source to the
unsaturated and saturated zones.  Geochemical models are
available that consider chemical processes that may be
active in the subsurface such as adsorption, precipitation,
oxidation/reduction, aqueous speciation, and kinetics.  

     Complex flow models have been developed to simulate the
effects of nearby pumping and discharging wells, fracture
flow, conduit flow in karst terrane, and multiphase flow for
fluids that are less dense or more dense than water. 
However, the use of the more complex models requires
additional data based on a thorough investigation of the
subsurface characteristics at a site as well as well-trained
users to apply the model correctly.

     Most of the ground-water flow and solute transport
models are deterministic. However, the use of stochastic
models, which allow for characterization of spatial and
temporal variability in systems, is increasing.  A few of
the models include a Monte Carlo capability for addressing
the uncertainty inherent in the input parameters. 
The EPA Multimedia Exposure Assessment Model (MULTIMED)

     EPA has developed a modeling package to meet the needs
of a large percentage of MSWLF unit owners and operators who
will require fate and transport modeling as part of the
performance-based design demonstration.  This model, the
Multimedia Exposure Assessment Model (MULTIMED), is intended
for use at sites where certain simplifying assumptions can
be made.  MULTIMED can be used in conjunction with a
separate leachate source model, such as HELP (Schroeder et
al., 1984).  Output from HELP is then used in MULTIMED to
demonstrate that either a landfill design or the specific
hydrogeologic conditions present at a site will prevent
contaminant concentrations in ground water from exceeding
the concentrations listed in Table 1 of Section 258.40. 
(Refer to pp. 4-53 and 6-8 for further discussion of HELP.) 
A description of MULTIMED follows with guidance for
determining if its use is appropriate for a given site.

     [NOTE:  Version 3.0 of the HELP model will be available
during the fall of 1993.  To obtain a copy, call EPA's
Office of Research and Development (ORD) in Cincinnati at
(513) 569-7871.]


     Overview of the Model

     The MULTIMED model consists of modules that estimate
contaminant releases to air, soil, ground water, or surface
water.  General information about the model and its theory
is provided in Salhotra et al. (1990).  Additionally,
information about the application of MULTIMED to MSWLF units
(developed by Sharp-Hansen et al. [1990]) is summarized
here.  In MULTIMED, a steady-state, one-dimensional,
semi-analytical module simulates flow in the unsaturated
zone.  The output from this module, which is water
saturation as a function of depth, is used as input to the
unsaturated zone transport module.  The latter simulates
transient, one-dimensional (vertical) transport in the
unsaturated zone and includes the effects of dispersion,
linear adsorption, and first-order decay.  Output from the
unsaturated zone modules is used as input to the
semi-analytical saturated zone transport module.  The latter
considers three-dimensional flow because the effects of
lateral or vertical dispersion may significantly affect the
model results. 

     Therefore, reducing the dimensions to one in this
module would produce inaccurate results.  The saturated zone
transport module also considers linear adsorption,
first-order decay, and dilution as a result of ground-water
recharge.  In addition, MULTIMED has the capability to
assess the impact of uncertainty in the model inputs on the
model output (contaminant concentration at a specified
point), using the Monte Carlo simulation technique.

     The simplifying assumptions required to obtain the
analytical solutions limit the complexity of the systems
that can be evaluated with MULTIMED.  The model does not
account for site-specific spatial variability (e.g., aquifer
heterogeneities), the shape of the land disposal facility,
site-specific boundary conditions, or multiple aquifers and
pumping wells.  Nor can MULTIMED simulate processes, such as
flow in fractures and chemical reactions between
contaminants, that may have a significant effect on the
concentration of contaminants at a site.  In more complex
systems, it may be beneficial to use MULTIMED as a
"screening level" model to allow the user to obtain an
understanding of the system.  A more complex model could
then be used if there are sufficient data.


Application of MULTIMED to MSWLF Units

     Procedures have been developed for the application of
MULTIMED to the design of MSWLF units.  They are explained
in Sharp-Hansen et al. (1990) and are briefly summarized
here.  The procedures are: 

     *    Collect site-specific hydrogeologic data,
          including amount of leachate generated (see
          Section 4.3.3);

     *    Identify the contaminant(s) to be simulated and
          the point of compliance;

     *    Propose a landfill design and determine the
          corresponding infiltration rate; then

     *    Run MULTIMED and calculate the dilution
          attenuation factor (DAF) (i.e., the factor by
          which the concentration is expected to decrease
          between the landfill unit and the point of
          compliance); and

     *    Multiply the initial contaminant concentration by
          the DAF and compare the resulting concentration to
          the MCLs to determine if the design will meet the
          standard.

     At this time, only contaminant transport in the
unsaturated and/or saturated zones can be modeled, because
the other options (i.e., surface water, air) have not yet
been thoroughly tested.  In addition, only steady-state
transport simulations are allowed.  No decay of the
contaminant source term is permitted; the concentration of
contaminants entering the aquifer system is assumed to be
constant over time.  The receptor (e.g., a drinking water
well) is located directly downgradient of the facility and
intercepts the contaminant plume; also, the contaminant
concentration is calculated at the top of the aquifer.

     The user should bear in mind that MULTIMED may not be
an appropriate model for some sites.  Some of the issues
that should be considered before modeling efforts proceed
are summarized in Table 4-2.  A "no" answer to any of the
questions in Table 4-2 may indicate that MULTIMED is not the
most appropriate model to use.  As stated above, MULTIMED
utilizes analytical and semi-analytical solution techniques
to solve the mathematical equations describing flow and
transport.  As a result, the representation of a system
simulated by the model is simple, and little or no spatial
or temporal variability is allowed for the parameters in the
system. Thus, a highly complex hydrogeologic system cannot
be accurately represented with MULTIMED.  


************************************************************
                          TABLE 4-2

                   ISSUES TO BE CONSIDERED
                  BEFORE APPLYING MULTIMED
              (from Sharp-Hansen et al., 1990)

     Objectives of the Study

     *    Is a "screening level" approach appropriate?
     *    Is modeling a "worst-case scenario"
          acceptable?

     Significant Processes Affecting Contaminant Transport

     *    Does MULTIMED simulate all the significant
          processes occurring at the site?

     *    Is the contaminant soluble in water and of
          the same density as water?

     Accuracy and Availability of the Data

     *    Have sufficient data been collected to obtain
          reliable results?

     *    What is the level of uncertainty associated
          with the data?

     *    Would a Monte Carlo simulation be useful?  If
          so, are the cumulative probability
          distributions for the parameters with
          uncertain values known?

     Complexity of the Hydrogeologic System

     *    Are the hydrogeologic properties of the
          system uniform?

     *    Is the flow in the aquifer uniform and
          steady?

     *    Is the site geometry regular?

     *    Does the source boundary condition require a
          transient or steady-state solution?
************************************************************


     The spatial characteristics assumed in MULTIMED should
be considered when applying MULTIMED to a site.  The
assumption of vertical, one-dimensional unsaturated flow may
be valid for facilities that receive uniform areal recharge. 
However, this assumption may not be valid for facilities
where surface soils (covers or daily backfill) or surface
slopes result in an increase of run-off in certain areas of
the facility, and ponding of precipitation in others.  In
addition, the simulation of one-dimensional, horizontal flow
in the saturated zone requires several simplifying
assumptions.  The saturated zone is treated as a single,
horizontal aquifer with uniform properties (e.g., hydraulic
conductivity).  The effects of pumping or discharging wells
on the ground-water flow system cannot be addressed with the
MULTIMED model.

     The MULTIMED model assumes steady-state flow in all
applications.  Some ground-water flow systems are in an
approximate "steady-state," in which the amount of water
entering the flow system equals the amount of water leaving
the system.  However, assuming steady-state conditions in a
system that exhibits transient behavior may produce
inaccurate results.


     MULTIMED may be run in either a deterministic or a
Monte Carlo mode.  The Monte Carlo method provides a means
of estimating the uncertainty in the results of a model, if
the uncertainty of the input variables is known or can be
estimated.  However, it may be difficult to determine the
cumulative probability distribution for a given parameter. 
Assuming a parameter probability distribution when the
distribution is unknown does not help reduce uncertainty. 
Furthermore, to obtain a valid estimate of the uncertainty
in the output, the model must be run numerous times
(typically several hundred times), which can be
time-consuming.  These issues should be considered before
utilizing the Monte Carlo technique.

     
4.3  COMPOSITE LINER AND LEACHATE COLLECTION SYSTEM 40 CFR
     Section 258.40

     4.3.1     Statement of Regulation

     (a) New MSWLF units and lateral expansions shall be
constructed:

     (1) See Statement of Regulation in Section 4.2.1 of
this guidance document for performance-based design
requirements.

     (2) With a composite liner, as defined in paragraph (b)
of this section and a leachate collection system that is
designed and constructed to maintain less than a 30-cm depth
of leachate over the liner, 

     (b) For purposes of this section, composite liner means
a system consisting of two components; the upper component
must consist of a minimum 30-mil flexible membrane liner
(FML), and the lower component must consist of at least a
two-foot layer of compacted soil with a hydraulic
conductivity of no more than 1 x 10-7 cm/sec.  FML
components consisting of high density polyethylene (HDPE)
shall be at least 60-mil thick.  The FML component must be
installed in direct and uniform contact with the compacted
soil component.


     4.3.2     Applicability

     New MSWLF units and expansions of existing MSWLF units
in States without approved programs must be constructed with
a composite liner and a leachate collection system (LCS)
that is designed to maintain a depth of leachate less than
30 cm (12 in.) above the liner.  A composite liner consists
of a flexible membrane liner (FML) installed on top of, and
in direct and uniform contact with, two feet of compacted
soil.  The FML must be at least 30-mil thick unless the FML
is made of HDPE, which must be 60-mil thick.  The compacted
soil liner must be at least two feet thick and must have a
hydraulic conductivity of no more than 1 x 10-7 cm/sec.

     Owners and operators of MSWLF units located in approved
States have the option of proposing a performance-based
design provided that certain criteria can be met (see
Section 4.2.2).


     4.3.3     Technical Considerations

     This section provides information on the components of
composite liner systems including soils, geomembranes, and
leachate collection systems.


Standard Composite Liner Systems

     The composite liner system is an effective hydraulic
barrier because it combines the complementary properties of
two different materials into one system:  1) compacted soil
with a low hydraulic conductivity; and
2) a FML (FMLs are also referred to as geomembranes). 
Geomembranes may contain defects including tears, improperly
bonded seams, and pinholes.  In the absence of an underlying
low-permeability soil liner, flow through a defect in a
geomembrane is essentially unrestrained.  The presence of a
low-permeability soil liner beneath a defect in the
geomembrane reduces leakage by limiting the flow rate
through the defect.

     Flow through the soil component of the liner is
controlled by the size of the defect in the geomembrane, the
available air space between the two liners into which
leachate can flow, the hydraulic conductivity of the soil
component, and the hydraulic head.  Fluid flow through soil
liners is calculated by Darcy's Law, where discharge (Q) is
proportional to the head loss through the soil (dh/dl) for a
given cross-sectional flow area (A) and hydraulic
conductivity (K) where:

                        Q = KA(dh/dl)

     Leakage through a geomembrane without defects is
controlled by Fick's first law, which describes the process
of liquid diffusion through the membrane liner.  The
diffusion process is similar to flow governed by Darcy's law
for soil liners except that diffusion is driven by
concentration gradients and not by hydraulic head.  Although
diffusion rates in geomembranes are several orders of
magnitude lower than comparable hydraulic flow rates in
low-permeability soil liners, construction of a completely
impermeable geomembrane is difficult.  The factor that most
strongly influences geomembrane performance is the presence
of imperfections such as improperly bonded seams, punctures
and pinholes.  A detailed discussion of leakage through
geomembranes and composite liners can be found in Giroud and
Bonaparte (1989 (Part I and Part II)).  A geomembrane
installed with excellent control over defects may yield the
equivalent of a one-centimeter-diameter hole per acre of
liner installed (Giroud and Bonaparte, 1989 (Part I and Part
II)).  If the geomembrane were to be placed over sand, this
size imperfection under one foot of constant hydraulic head
could be expected to account for as much as 3,300
gal/acre/day (31,000 liters/hectare/ day) of leakage.  Based
upon measurements of actual leakage through liners at
facilities that have been built under rigorous control,
Bonaparte and Gross (1990) have estimated an actual leakage
rate, under one foot of constant head, of 200
liters/hectare/day or about 21 gallons/acre/day for landfill
units.

     The uniformity of the contact between the geomembrane
and the soil liner is extremely important in controlling the
effective flow area of leachate through the soil liner. 
Porous material, such as drainage sand, filter fabric, or
other geofabric, should not be placed between the
geomembrane and the low permeability soil liner.  Porous
materials will create a layer of higher hydraulic
conductivity, which will increase the amount of leakage
below an imperfection in the geomembrane.  Construction
practices during the installation of the soil and the
geomembrane affect the uniformity of the geomembrane/soil
interface, and strongly influence the performance of the
composite liner system.

     
Soil Liner

     The following subsections discuss soil liner
construction practices including thickness requirements,
lift placement, bonding of lifts, test methods, prerequisite
soil properties, quality control, and quality assurance
activities.


     Thickness

     Two feet of soil is generally considered the minimum
thickness needed to obtain adequate compaction to meet the
hydraulic conductivity requirement. This thickness is
considered necessary to minimize the number of cracks or
imperfections through the entire liner thickness that could
allow leachate migration.  Both lateral and vertical
imperfections may exist in a compacted soil.  The two-foot
minimum thickness is believed to be sufficient to inhibit
hydraulic short-circuiting of the entire layer.


     Lift Thickness 

     Soil liners should be constructed in a series of
compacted lifts.  Determination of appropriate lift
thickness is dependent on the soil characteristics,
compaction equipment, firmness of the foundation materials,
and the anticipated compactive effort needed to achieve the
required soil hydraulic conductivity.  Soil liner lifts
should be thin enough to allow adequate compactive effort to
reach the lower portions of the lift.  Thinner lifts also
provide greater assurance that sufficient compaction can be
achieved to provide good, homogeneous bonding between
subsequent lifts.  Adequate compaction of lift thickness
between five and ten inches is possible if appropriate
equipment is used (USEPA, 1988).  Nine-inch loose lift
thicknesses that will yield a 6-inch soil layer also have
been recommended prior to compaction (USEPA, 1990a).

     Soil liners usually are designed to be of uniform
thickness with smooth slopes over the entire facility. 
Thicker areas may be considered wherever recessed areas for
leachate collection pipes or collection sumps are located. 
Extra thickness and compactive efforts near edges of the
side slopes may enhance bonding between the side slopes and
the bottom liner.  In smaller facilities, a soil liner may
be designed for installation over the entire area, but in
larger or multi-cell facilities, liners may be designed in
segments.  If this is the case, the design should address
how the old and new liner segments will be bonded together
(U.S. EPA, 1988).


     Bonding Between Lifts

     It is not possible to construct soil liners without
some microscopic and/or macroscopic zones of higher and
lower hydraulic conductivity.  Within individual lifts,
these preferential pathways for fluid migration are
truncated by the bonded zone between the lifts.  If good
bonding between the lifts is not achieved during
construction, the vertical pathways may become connected by
horizontal pathways at the lift interface, thereby
diminishing the performance of the hydraulic barrier.

     Two methods may be used to ensure proper bonding
between lifts.  Kneading or blending a thinner, new lift
with the previously compacted lift may be achieved by using
a footed roller with long feet that can fully penetrate a
loose lift of soil.  If the protruding rods or feet of a
sheepsfoot roller are sufficient in length to penetrate the
top lift and knead the previous lift, good bonding may be
achieved.  Another method includes scarifying (roughening),
and possibly wetting, the top inch or so of the last lift
placed with a disc harrow or other similar equipment before
placing the next lift.


     Placement of Soil Liners on Slopes

     The method used to place the soil liner on side slopes
depends on the angle and length of the slope.  Gradual
inclines from the toe of the slope enable continuous
placement of the lifts up the slopes and provide better
continuity between the bottom and sidewalls of the soil
liner.  When steep slopes are encountered, however, lifts
may need to be placed and compacted horizontally due to the
difficulties of operating heavy compaction equipment on
steeper slopes.

     When sidewalls are compacted horizontally, it is
important to tie in the edges with the bottom of the soil
liner to reduce the probability of seepage planes (USEPA,
1988).  A significant amount of additional soil liner
material will be required to construct the horizontal lifts
since the width of the lifts has to be wide enough to
accommodate the compaction equipment.  After the soil liner
is constructed on the side slopes using this method, it can
be trimmed back to the required thickness.  The trimmed
surface of the soil liner should be sealed by a smooth-drum
roller.  The trimmed excess materials can be reused provided
that they meet the specified moisture-density requirements.


     Hydraulic Conductivity

     Achieving the hydraulic conductivity standard depends
on the degree of compaction, compaction method, type of
clay, soil moisture content, and density of the soil during
liner construction.  Hydraulic conductivity is the key
design parameter when evaluating the acceptability of the
constructed soil liner.  The hydraulic conductivity of a
soil depends, in part, on the viscosity and density of the
fluid flowing through it.  While water and leachate can
cause different test results, water is an acceptable fluid
for testing the compacted soil liner and source materials. 
The effective porosity of the soil is a function of size,
shape, and area of the conduits through which the liquid
flows.  The hydraulic conductivity of a partially saturated
soil is less than the hydraulic conductivity of the same
soil when saturated.  Because invading water only flows
through water-filled voids (and not air-filled voids), the
dryness of a soil tends to lower permeability.  Hydraulic
conductivity testing should be conducted on samples that are
fully saturated to attempt to measure the highest possible
hydraulic conductivity.

     EPA has published Method 9100 in publication SW-846
(Test Methods for Evaluating Solid Waste) to measure the
hydraulic conductivity of soil samples.  Other methods
appear in the U.S. Army Corps of Engineers Engineering
Manual 1110-2-1906  (COE, 1970) and the newly published
"Measurement of Hydraulic Conductivity of Saturated Porous
Materials Using a Flexible Wall Permeameter" (ASTM D-5084). 
To verify full saturation of the sample, this latter method
may be performed with back pressure saturation and
electronic pore pressure measurement.  


     Soil Properties

     Soils typically possess a range of physical
characteristics, including particle size, gradation, and
plasticity, that affect their ability to achieve a hydraulic
conductivity of 1 x 10-7 cm/sec.  Testing methods used to
characterize proposed liner soils should include grain size
distribution (ASTM D-422), Atterberg limits (ASTM D-4318),
and compaction curves depicting moisture and density
relationships using the standard or modified Proctor (ASTM
D-698 or ASTM D-1557), whichever is appropriate for the
compaction equipment used and the degree of firmness of the
foundation materials.

     Liner soils usually have at least 30 percent fines
(fine silt- and clay-sized particles).  Some soils with less
than 30 percent fines may be worked to obtain hydraulic
conductivities below 1 x 10-7 cm/sec, but use of these soils
requires greater control of construction practices and
conditions.

     The soil plasticity index (PI), which is determined
from the Atterberg limits (defined by the liquid limit minus
the plastic limit), should generally be greater than 10
percent.  However, soils with very high PI, (greater than 30
percent), are cohesive and sticky and become difficult to
work with in the field.  When high PI soils are too dry
during placement, they tend to form hard clumps (clods) that
are difficult to break down during compaction.  Preferential
flow paths may be created around the clods allowing leachate
to migrate at a relatively high rate.

     Soil particles or rock fragments also can create
preferential flow paths.  For this reason, soil particles or
rock fragments should be less than 3 inches in diameter so
as not to affect the overall hydraulic performance of the
soil liner (USEPA, 1989).

     The maximum density of a soil will be achieved at the
optimum water content, but this point generally does not
correspond to the point at which minimum hydraulic
conductivity is achieved.  Wet soils, however, have low
shear strength and high potential for desiccation cracking. 
Care should be taken not to compromise other engineering
properties such as shear strengths of the soil liner by
excessively wetting the soil liner.  Depending on the
specific soil characteristics, compaction equipment and
compactive effort, the hydraulic conductivity criterion may
be achieved at moisture values of 1 to 7 percent above the
optimum moisture content.

     Although the soil may possess the required properties
for successful liner construction, the soil liner may not
meet the hydraulic conductivity criterion if the
construction practices used to install the liner are not
appropriate and carefully controlled.  Construction quality
control and quality assurance will be discussed in a later
section.


     Amended Soils

     If locally available soils do not possess properties to
achieve the specified hydraulic conductivity, soil additives
can be used.  Soil additives, such as bentonite or other
clay materials, can decrease the hydraulic conductivity of
the native soil (USEPA, 1988b).

     Bentonite may be obtained in a dry, powdered form that
is relatively easy to blend with on-site soils.  Bentonite
is a clay mineral (sodium-montmorillonite) that expands when
it comes into contact with water (hydration), by absorbing
the water within the mineral matrix.  This property allows
relatively small amounts of bentonite (5 to 10 percent) to
be added to a noncohesive soil (sand) to make it more
cohesive (U.S. EPA, 1988b).  Thorough mixing of additives to
cohesive soils (clay) is difficult and may lead to
inconsistent results with respect to complying with the
hydraulic conductivity criterion.

     The most common additive used to amend soils is sodium
bentonite.  The disadvantage of using sodium bentonite
includes its vulnerability to degradation as a result of
contact with chemicals and waste leachates (U.S. EPA, 1989).

     Calcium bentonite, although more permeable than sodium
bentonite, also is used as a soil amendment.  Approximately
twice as much calcium bentonite typically is needed to
achieve a hydraulic conductivity comparable to that of
sodium bentonite.

     Soil/bentonite mixtures generally require central plant
mixing by means of a pugmill, cement mixer, or other mixing
equipment where water can be added during the process. 
Water, bentonite content, and particle size distribution
must be controlled during mixing and placement.  Spreading
of the soil/bentonite mixture may be accomplished in the
same manner as the spreading of natural soil liners, by
using scrapers, graders, bulldozers, or a continuous asphalt
paving machine (U.S. EPA, 1988).

     Materials other than bentonite, including lime, cement,
and other clay minerals such as atapulgite, may be used as
soil additives (U.S. EPA, 1989).  For more information
concerning soil admixtures, the reader is referred to the
technical resource document on the design and construction
of clay liners (U.S. EPA, 1988).


     Testing

     Prior to construction of a soil liner, the relationship
between water content, density, and hydraulic conductivity
for a particular soil should be established in the
laboratory.  Figure 4-5 shows the influence of molding water
content (moisture content of the soil at the time of
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.  The optimum
moisture content of the soil is related to a peak value of
dry density known as maximum dry density.  Maximum dry
density is achieved at the optimum moisture content.


************************************************************
                         FIGURE 4-5

         Hydraulic Conductivity and Dry Unit Weight 
           as a Function of Molding Water Content
                          [Graphic]
************************************************************


     The lowest hydraulic conductivity of compacted clay
soil is achieved when the soil is compacted at a moisture
content slightly higher than the optimum moisture content,
generally in the range of 1 to 7 percent (U.S. EPA, 1989). 
When compacting clay, water content and compactive effort
are the two factors that should be controlled to meet the
maximum hydraulic conductivity criterion. 

     It is impractical to specify and construct a clay liner
to a specific moisture content and a specific compaction
(e.g., 5 percent wet of optimum and 95 percent modified
Proctor density).  Moisture content can be difficult to
control in the field during construction; therefore, it may
be more appropriate to specify a range of moisture contents
and corresponding soil densities (percent compaction) that
are considered appropriate to achieve the required hydraulic
conductivity.  Benson and Daniel (U.S. EPA, 1990) propose
water content and density criteria for the construction of
clay liners in which the moisture-density criteria ranges
are established based on hydraulic conductivity test
results.  This type of approach is recommended because of
the flexibility and guidance it provides to the construction
contractor during soil placement.  Figure 4-6 presents
compaction data as a function of dry unit weight and molding
water content for the construction of clay liners.  The
amount of soil testing required to determine these
construction parameters is dependent on the degree of
natural variability of the source material.  


************************************************************
                         FIGURE 4-6

               Compaction Data for Silty Clay
                          [Graphic]
************************************************************


     Quality assurance and quality control of soil liner
materials involve both laboratory and field testing. 
Quality control tests are performed to ascertain compaction
requirements and the moisture content of material delivered
to the site.  Field tests for quality assurance provide an
opportunity to check representative areas of the liner for
conformance to compaction specifications, including density
and moisture content.  Quality assurance laboratory testing
is usually conducted on field samples for determination of
hydraulic conductivity of the in-place liner.  Laboratory
testing allows full saturation of the soil samples and
simulates the effects of large overburden stress on the
soil, which cannot be done conveniently in the field (U.S.
EPA, 1989).

     Differences between laboratory and field conditions
(e.g., uniformity of material, control of water content,
compactive effort, compaction equipment) may make it
unlikely that minimum hydraulic conductivity values measured
in the laboratory on remolded, pre-construction borrow
source samples are the same as the values achieved during
actual liner construction.  Laboratory testing on remolded
soil specimens does not account for operational problems
that may result in desiccation, cracking, poor bonding of
lifts, and inconsistent degree of compaction on sidewalls
(U.S. EPA, 1988b).  The relationship between field and
laboratory hydraulic conductivity testing has been
investigated by the U.S. Environmental Protection Agency
using field case studies (U.S. EPA, 1990c).

     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. 
Four types of in situ hydraulic conductivity tests generally
are used:  borehole tests, porous probes, infiltrometer
tests, and underdrain tests.  A borehole test is conducted
by drilling a hole, then filling the hole with water, and
measuring the rate at which water percolates into the
borehole.  In the borehole test, water also can percolate
through the sidewalls of the borehole.  As a result, the
measured hydraulic conductivity is usually higher than that
measured by other one-dimensional field testings.

     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.  The two types of infiltrometers
most widely used are open and sealed.  Open rings are less
desirable because, with a hydraulic conductivity of 10-7
cm/sec, it is difficult to detect a 0.002 inch per day drop
in water level of the pond from evaporation and other
losses.

     With sealed rings, very low rates of flow can be
measured.  However, single-ring infiltrometers allow lateral
flow beneath the ring, which can complicate the
interpretation of test results.  Single rings are also
susceptible to the effects of temperature variation; as the
water temperature increases, the entire system expands.  As
it cools down, the system contracts.  This situation could
lead to erroneous measurements when the rate of flow is
small.

     The sealed double-ring infiltrometer has proven to be
the most successful method and is the one currently used. 
The outer ring forces infiltration from the inner ring to be
more or less one-dimensional.  Covering the inner ring with
water insulates it substantially from temperature variation.

     Underdrains, the fourth type of in situ test, are the
most accurate in situ permeability testing device because
they measure exactly what migrates from the bottom of the
liner.  However, under-drains are slow to generate data for
low permeability liners, because of the length of time
required to accumulate measur-able flow.  Also, underdrains
must be installed during construction, so fewer underdrains
are used than other kinds of testing devices.

     Field hydraulic conductivity tests are not usually
performed on the completed liner because the tests may take
several weeks to complete (during which time the liner may
be damaged by desiccation or freezing temperatures) and
because large penetrations must be made into the liner.  If
field conductivity tests are performed, they are usually
conducted on a test pad.  The test pad should be constructed
using the materials and methods to be used for the actual
soil liner.  The width of a test pad is usually the width of
three to four construction vehicles, and the length is one
to two times the width.  Thickness is usually two to three
feet.  Test pads can be used as a means for verifying that
the proposed materials and construction procedures will meet
performance objectives.  If a test pad is constructed, if
tests verify that performance objectives have been met, and
if the actual soil liner is constructed to standards that
equal or exceed those used in building the test pad (as
verified through quality assurance), then the actual soil
liner should meet or exceed performance objectives.

     Other than the four types of field hydraulic
conductivity tests described earlier, ASTM D 2937 "Standard
Test Method for Density of Soil in Place by the
Drive-Cylinder Method" may be used to obtain in-place
hydraulic conductivity of the soil liner.  This test method
uses a U.S. Army Corps of Engineers surface soil sampler to
drive a thin-walled cylinder (typically 3-inch by 3-inch)
into a completed lift of the soil liner to obtain relatively
undisturbed samples for laboratory density and hydraulic
conductivity testings.  This test can provide useful
correlation to other field and quality assurance testing
results (e.g, Atterberg limits, gradation, in-place moisture
and density of the soil liner) to evaluate the in-place
hydraulic conductivity of the soil liner.


     Soil Liner Construction

     Standard compaction procedures are usually employed
when constructing soil liners.  The following factors
influence the degree and quality of compaction:

     *    Lift thickness;

     *    Full scale or segmented lift placement;

     *    Number of equipment passes;

     *    Scarification between lifts;

     *    Soil water content; and

     *    The type of equipment and compactive effort.

     The method used to compact the soil liner is an
important factor in achieving the required minimum hydraulic
conductivity.  Higher degrees of compactive effort increase
soil density and lower the soil hydraulic conductivity for a
given water content.  The results of laboratory compaction
tests do not necessarily correlate directly with the amount
of compaction that can be achieved during construction.

     Heavy compaction equipment (greater than 25,000 lbs or
11,300 kg) is typically used when building the soil liner to
maximize compactive effort (U.S. EPA, 1989).  The preferred
field compaction equipment is a sheepsfoot roller with long
feet that fully penetrates  loose lifts of soil and provides
higher compaction while kneading the clay particles
together.  The shape and depth of the feet are important;
narrow, rod-like feet with a minimum length of about seven
inches provide the best results.  A progressive change from
the rod-like feet to a broader foot may be necessary in some
soils after initial compaction, to allow the roller to walk
out of the compacted soil.  The sheepsfoot feet also aid in
breaking up dry clods (see Soil Properties in this section). 
Mechanical road reclaimers, which are typically used to
strip and re-pave asphalt, can be extremely effective in
reducing soil clod size prior to compaction and in
scarifying soil surfaces between lifts.  Other equipment
that has been used to compact soil includes discs and
rototillers.

     To achieve adequate compaction, the lift thickness
(usually five to nine inches) may be decreased or the number
of passes over the lift may be increased.  Generally,
compaction equipment should pass over the soil liner five to
twenty times to attain the compaction needed to comply with
the minimum hydraulic conductivity criterion (U.S. EPA,
1989).

     Efforts made to reduce clod size during excavation and
placement of the soil for the liner should improve the
chances for achieving low hydraulic conductivity in several
ways.  Keeping clods in the soil liner material small will
facilitate a more uniform water content.  Macropores between
clod remnants can result in unacceptably high field
hydraulic conductivity.

     Opinions differ on acceptable clod sizes in the
uncompacted soil.  Some suggest a maximum of one to three
inches in diameter, or no larger than one-half the lift
thickness.  The main objective is to remold all clods in the
compaction process to keep hydraulic conductivity values
consistent throughout the soil liner (U.S. EPA, 1988).


Geomembranes

     Geomembranes are relatively thin sheets of flexible
thermoplastic or thermoset polymeric materials that are
manufactured and prefabricated at a factory and transported
to the site.  Because of their inherent impermeability, use
of geomembranes in landfill unit construction has increased. 
The design of the side slope, specifically the friction
between natural soils and geosynthetics, is critical and
requires careful review.


     Material Types and Thicknesses

     Geomembranes are made of one or more polymers along
with a variety of other ingredients such as carbon black,
pigments, fillers, plasticizers, processing aids,
crosslinking chemicals, anti-degradants, and biocides.  The
polymers used to manufacture geomembranes include a wide
range of plastics and rubbers differing in properties such
as chemical resistance and basic composition (U.S. EPA, 1983
and U.S. EPA, 1988e).  The polymeric materials may be
categorized as follows:

     *    Thermoplastics such as polyvinyl chloride (PVC);

     *    Crystalline thermoplastics such as high density
          polyethylene (HDPE), very low density polyethylene
          (VLDPE), and linear low density polyethylene
          (LLDPE); and

     *    Thermoplastic elastomers such as chlorinated
          polyethylene (CPE) and chlorosulfonated
          polyethylene (CSPE).

     The polymeric materials used most frequently as
geomembranes are HDPE, PVC, CSPE, and CPE.  The thicknesses
of geomembranes range from 20 to 120 mil (1 mil = 0.001
inch) (U.S. EPA, 1983 and U.S. EPA, 1988e).  The recommended
minimum thickness for all geomembranes is 30 mil, with the
exception of HDPE, which must be at least 60 mil to allow
for proper seam welding.  Some geomembranes can be
manufactured by a calendering process with fabric
reinforcement, called scrim, to provide additional tensile
strength and dimensional stability.  


     Chemical and Physical Stress Resistance

     The design of the landfill unit should consider
stresses imposed on the liner by the design configuration. 
These stresses include the following:

     *    Differential settlement in foundation soils;

     *    Strain requirements at the anchor trench; and

     *    Strain requirements over long, steep side slopes.

     An extensive body of literature has been developed by
manufacturers and independent researchers on the physical
properties of liners.  Geosynthetic design equations are
presented in several publications including Kastman (1984),
Koerner (1990), and U.S. EPA (1988e).

     The chemical resistance of a geomembrane to leachate
has traditionally been considered a critical issue for
Subtitle C (hazardous waste) facilities where highly
concentrated solvents may be encountered.  Chemical
resistance testing of geomembranes may not be required for
MSWLF units containing only municipal solid waste; EPA's
data base has shown that leachate from MSWLF units is not
aggressive to these types of materials.  Testing for
chemical resistance may be warranted considering the waste
type, volumes, characteristics, and amounts of small
quantity generator waste or other industrial waste present
in the waste stream.  The following guidance is provided in
the event such testing is of interest to the owner or
operator.

     EPA's Method 9090 in SW-846 is the established test
procedure used to evaluate degradation of geomembranes when
exposed to hazardous waste leachate.  In the procedure, the
geomembrane is 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 thirty days.  A software system entitled
Flexible Liner Evaluation Expert (FLEX), designed to assist
in the hazardous waste permitting process, may aid in
interpreting EPA Method 9090 test data (U.S. EPA, 1989).  A
detailed discussion of both Method 9090 and FLEX is
available from EPA.

     It is imperative that a geomembrane liner maintain its
integrity during exposure to short-term and long-term
mechanical stresses.  Short-term mechanical stresses include
equipment traffic during the installation of a liner system,
as well as thermal expansion and shrinkage of the
geomembrane during the construction and operation of the
MSWLF unit.  Long-term mechanical stresses result from the
placement of waste on top of the liner system and from
subsequent differential settlement of the subgrade (U.S.
EPA, 1988a).

     Long-term success of the liner requires adequate
friction between the components of a liner system,
particularly the soil subgrade and the geomembrane, and
between geosynthetic components, so that slippage or
sloughing does not occur on the slopes of the unit. 
Specifically, the foundation slopes and the subgrade
materials must be considered in design equations to
evaluate:

     *    The ability of a geomembrane to support its own
          weight on the side slopes;

     *    The ability of a geomembrane to withstand
          down-dragging during and after waste placement;

     *    The best anchorage configuration for the
          geomembrane;

     *    The stability of a soil cover on top of a
          geomembrane; and

     *    The stability of other geosynthetic components
          such as geotextile or geonet on top of a
          geomembrane.

     These requirements may affect the choice of geomembrane
material, including polymer type, fabric reinforcement,
thickness, and texture (e.g., smooth or textured for HDPE)
(U.S. EPA, 1988).  PVC also can be obtained in a roughened
or file finish to increase the friction angle.

     Design specifications should indicate the type of raw
polymer and manufactured sheet to be used as well as the
requirements for the delivery, storage, installation, and
sampling of the geomembrane.  Material properties can be
obtained from the manufacturer-supplied average physical
property values, which are published in the Geotechnical
Fabrics Report's Specifier's Guide and updated annually. 
The minimum tensile properties of the geomembrane must be
sufficient to satisfy the stresses anticipated during the
service life of the geomembrane.  Specific raw polymer and
manufactured sheet specifications and test procedures
include (U.S. EPA, 1988e, and Koerner, 1990):

     Raw Polymer Specifications

     *    Density (ASTM D-1505);

     *    Melt index (ASTM D-1238);

     *    Carbon black (ASTM D-1603); and

     *    Thermogravimetric analysis (TGA) or differential
          scanning calorimetry (DSC).

     Manufactured Sheet Specifications

     *    Thickness (ASTM D-1593);

     *    Tensile properties (ASTM D-638);

     *    Tear resistance (ASTM D-1004);

     *    Carbon black content (ASTM D- 1603);

     *    Carbon black dispersion (ASTM D-3015);

     *    Dimensional stability (ASTM D-1204); and

     *    Stress crack resistance (ASTM D- 1693).

     Geomembranes may have different physical
characteristics, depending on the type of polymer and the
manufacturing process used, that can affect the design of a
liner system.  When reviewing manufacturers' literature, it
is important to remember that each manufacturer may use more
than one polymer or resin type for each grade of geomembrane
and that the material specifications may be generalized to
represent several grades of material.


     Installation

     Installation specifications should address installation
procedures specific to the properties of the liner
installed.  The coefficient of thermal expansion of the
geomembrane sheet can affect its installation and its
service performance.  The geomembrane should lie flat on the
underlying soil.  However, shrinkage and expansion of the
sheeting, due to changes in temperature during installation,
may result in excessive wrinkling or tension in the
geomembrane.  Wrinkles on the geomembrane surface will
affect the uniformity of the soil-geomembrane interface and
may result in leakage through imperfections.  Excessive
tautness of the geomembrane may affect its ability to resist
rupture from localized stresses on the seams or at the toe
of slopes where bridging over the subgrade may occur during
installation.  In addition to thermal expansion and
contraction of the geomembrane, residual stresses from
manufacturing remain in some geomembranes and can cause
non-uniform expansion and contraction during construction. 
Some flexibility is needed in the specifications for
geomembrane selection to allow for anticipated dimensional
changes resulting from thermal expansion and contraction
(U.S. EPA, 1988).

     Technical specifications for geomembranes also should
include:  information for protection of the material during
shipping, storage and handling; quality control
certifications provided by the manufacturer or fabricator
(if panels are constructed); and quality control testing by
the contractor, installer, or a construction quality
assurance (CQA) agent.  Installation procedures addressed by
the technical specifications include a geomembrane layout
plan, deployment of the geomembrane at the construction
site, seam preparation, seaming methods, seaming temperature
constraints, detailed procedures for repairing and
documenting construction defects, and sealing of the
geomembrane to appurtenances, both adjoining and penetrating
the liner.  The performance of inspection activities,
including both non-destructive and destructive quality
control field testing of the sheets and seams during
installation of the geomembrane, should be addressed in the
technical specifications.  Construction quality assurance is
addressed in an EPA guidance document (USEPA, 1992).

     The geomembrane sheeting is shipped in rolls or panels
from the supplier, manufacturer, or fabricator to the
construction site.  Each roll or panel may be labeled
according to its position on the geomembrane layout plan to
facilitate installation.  Upon delivery, the geomembrane
sheeting should be inspected to check for damage that may
have occurred during shipping. (U.S. EPA, 1992).

     Proper storage of the rolls or panels prior to
installation is essential to the final performance of the
geomembrane.  Some geomembrane materials are sensitive to
ultraviolet exposure and should not be stored in direct
sunlight prior to installation.  Others, such as CSPE and
CPE, are sensitive to moisture and heat and can partially
crosslink or block (stick together) under improper storage
conditions.  Adhesives or welding materials, which are used
to join geomembrane panels, also should be stored
appropriately (U.S. EPA, 1992).

     Visual inspection and acceptance of the soil liner
subgrade should be conducted prior to installing the
geomembrane.  The surface of the subgrade should meet design
specifications with regard to lack of protruding objects,
grades, and thickness.  Once these inspections are conducted
and complete, the geomembrane may be installed on top of the
soil liner.  If necessary, other means should be employed to
protect the subgrade from precipitation and erosion, and to
prevent desiccation, moisture loss, and erosion from the
soil liner prior to geomembrane placement.  Such methods may
include placing a plastic tarp on top of completed portions
of the soil liner (USEPA, 1992).  In addition, scheduling
soil liner construction slightly ahead of the geomembrane
and drainage layer placement can reduce the exposure of the
soil liner to the elements.

     Deployment, or placement, of the geomembrane panels or
rolls should be described in the geomembrane layout plan. 
Rolls of sheeting, such as HDPE, generally can be deployed
by placing a shaft through the core of the roll, which is
supported and deployed using a front-end loader or a winch. 
Panels composed of extremely flexible liner material such as
PVC are usually folded on pallets, requiring workers to
manually unfold and place the geomembrane.  Placement of the
geomembrane goes hand-in-hand with the seaming process; no
more than the amount of sheeting that can be seamed during a
shift or work day should be deployed at any one time (USEPA,
1988).  Panels should be weighted with sand bags if wind
uplift of the membrane or excessive movement from thermal
expansion is a potential problem.  Proper stormwater control
measurements should be employed during construction to
prevent erosion of the soil liner underneath the geomembrane
and the washing away of the geomembrane.

     Once deployment of a section of the geomembrane is
complete and each section has been visually inspected for
imperfections and tested to ensure that it is the specified
thickness, seaming of the geomembrane may begin.  Quality
control/quality assurance monitoring of the seaming process
should be implemented to detect inferior seams.  Seaming can
be conducted either in the factory or in the field.  Factory
seams are made in a controlled environment and are generally
of high quality, but the entire seam length (100 percent)
still should be tested non-destructively (U.S. EPA, 1988). 
Destructive testing should be done at regular intervals
along the seam (see below).

     Consistent quality in fabricating field seams is
critical to liner performance, and conditions that may
affect seaming should be monitored and controlled during
installation.  An inspection should be conducted in
accordance with a construction quality assurance plan to
document the integrity of field seams.  Factors affecting
the seaming process include (U.S. EPA, 1988):

     *    Ambient temperature at which the seams are made;

     *    Relative humidity;

     *    Control of panel lift-up by wind;

     *    The effect of clouds on the geomembrane
          temperature;

     *    Water content of the subsurface beneath the
          geomembrane;

     *    The supporting surface on which the seaming is
          bonded;

     *    The skill of the seaming crew;

     *    Quality and consistency of the chemical or welding
          material;

     *    Proper preparation of the liner surfaces to be
          joined;

     *    Moisture on the seam interface; and

     *    Cleanliness of the seam interface (e.g., the
          amount of airborne dust and debris present).

     Depending on the type of geomembrane, several bonding
systems are available for the construction of both factory
and field seams.  Bonding methods include solvents, heat
seals, heat guns, dielectric seaming, extrusion welding, and
hot wedge techniques.  To ensure the integrity of the seams,
a geomembrane should be seamed using the bonding system
recommended by the manufacturer (U.S. EPA, 1988).  EPA has
developed a field seaming manual for all types of
geomembranes (U.S. EPA, 1991a).

     Thermal methods of seaming require cleanliness of the
bonding surfaces, heat, pressure, and dwell time to produce
high quality seams.  The requirements for adhesive systems
are the same as those for thermal systems, except that the
adhesive takes the place of the heat.  Sealing the
geomembrane to appurtenances and penetrating structures
should be performed in accordance with detailed drawings
included in the design plans and approved specifications.

     An anchor trench along the perimeter of the cell
generally is used to secure the geomembrane during
construction (to prevent sloughing or slipping down the
interior side slopes).  Run out calculations (Koerner, 1990)
are available to determine the depth of burial at a trench
necessary to hold a specified length of membrane, or
combination of membrane and geofabric or geotextile.  If
forces larger than the tensile strength of the membrane are
inadvertently developed, then the membrane could tear.  For
this reason, the geomembrane should be allowed to slip or
give in the trench after construction to prevent such
tearing.  However, during construction, the geomembrane
should be anchored according to the detailed drawings
provided in the design plans and specifications (USEPA,
1988).

     Geomembranes that are subject to damage from exposure
to weather and work activities should be covered with a
layer of soil as soon as possible after quality assurance
activities associated with geomembrane testing are
completed.  Soil should be placed without driving
construction vehicles directly on the geomembrane.  Light
ground pressure bulldozers may be used to push material out
in front over the liner, but the operator must not attempt
to push a large pile of soil forward in a continuous manner
over the membrane.  Such methods can cause localized
wrinkles to develop and overturn in the direction of
movement.  Overturned wrinkles create sharp creases and
localized stresses in the geomembrane that could lead to
premature failure.  Instead, the operator should continually
place smaller amounts of soil or drainage material working
outward over the toe of the previously placed material. 
Alternatively, large backhoes can be used to place soil over
the geomembrane that can later be spread with a bulldozer or
similar equipment.  Although such methods may sound tedious
and slow, in the long run they will be faster and more
cost-effective than placing too much material too fast and
having to remobilize the liner installer to repair damaged
sections of the geomembrane.  The QA activities conducted
during construction also should include monitoring the
contractor's activities on top of the liner to avoid damage
to installed and accepted geomembranes.


Leachate Collection Systems

     Leachate refers to liquid that has passed through or
emerged from solid waste and contains dissolved, suspended,
or immiscible materials removed from the solid waste.  At
MSWLF units, leachate is typically aqueous with limited, if
any, immiscible fluids or dissolved solvents.  The primary
function of the leachate collection system is to collect and
convey leachate out of the landfill unit and to control the
depth of the leachate above the liner.  The leachate
collection system (LCS) should be designed to meet the
regulatory performance standard of maintaining less than 30
cm (12 inches) depth of leachate, or "head," above the
liner.  The 30-cm head allowance is a design standard and
the Agency recognizes that this design standard may be
exceeded for relatively short periods of time during the
active life of the unit.  Flow of leachate through
imperfections in the liner system increases with an increase
in leachate head above the liner.  Maintaining a low
leachate level above the liner helps to improve the
performance of the composite liner.

     Leachate is generally collected from the landfill
through sand drainage layers, synthetic drainage nets, or
granular drainage layers with perforated plastic collection
pipes, and is then removed through sumps or gravity drain
carrier pipes.  LCS's should consist of the following
components (U.S. EPA, 1988):

     *    A low-permeability base (in this case a composite
          liner);

     *    A high-permeability drainage layer, constructed of
          either natural granular materials (sand and
          gravel) or synthetic drainage material (e.g.,
          geonet) placed directly on the FML, or on a
          protective bedding layer (e.g., geofabric)
          directly overlying the liner;

     *    Perforated leachate collection pipes within the
          high-permeability drainage layer to collect
          leachate and carry it rapidly to a sump or
          collection header pipe;

     *    A protective filter layer over the high
          permeability drainage material, if necessary, to
          prevent physical clogging of the material by
          fine-grained material; and

     *    Leachate collection sumps or header pipe system
          where leachate can be removed.

     The design, construction, and operation of the LCS
should maintain a maximum height of leachate above the
composite liner of 30 cm (12 in).  Design guidance for
calculating the maximum leachate depth over a liner for
granular drainage systems materials is provided in the
reference U.S. EPA (1989).  The leachate head in the layer
is a function of the liquid impingement rate, bottom slope,
pipe spacing, and drainage layer hydraulic conductivity. 
The impingement rate is estimated using a complex liquid
routing procedure.  If the maximum leachate depth exceeds 30
cm for the system, except for short-term occurrences, the
design should be modified to improve its efficiency by
increasing grade, decreasing pipe spacing, or increasing the
hydraulic conductivity (transmissivity) of the drainage
layer (U.S. EPA, 1988).


     Grading of Low-Permeability Base

     The typical bottom liner slope is a minimum of two
percent after allowances for settlement at all points in
each system.  A slope is necessary for effective gravity
drainage through the entire operating and post-closure
period.  Settlement estimates of the foundation soils should
set this two-percent grade as a post-settlement design
objective (U.S. EPA, 1991b).


     High-Permeability Drainage Layer

     The high-permeability drainage layer is placed directly
over the liner or its protective bedding layer at a slope of
at least two percent (the same slope necessary for the
composite liner).  Often the selection of a drainage
material is based on the on-site availability of natural
granular materials.  In some regions of the country, hauling
costs may be very high for sand and gravel, or appropriate
materials may be unavailable; therefore, the designer may
elect to use geosynthetic drainage nets (geonets) or
synthetic drainage materials as an alternative.  Frequently,
geonets are substituted for granular materials on steep
sidewalls because maintaining sand on the slope during
construction and operation of the landfill unit is more
difficult (U.S. EPA, 1988).


     Soil Drainage Layers 

     If the drainage layer of the leachate collection system
is constructed of granular soil materials (e.g., sand and
gravel), then it should be demonstrated that this granular
drainage layer has sufficient bearing strength to support
expected loads.  This demonstration will be similar to that
required for the foundations and soil liner (U.S. EPA,
1988).

     If the landfill unit is designed on moderate-to-steep
(15 percent) grades, the landfill design should include
calculations demonstrating that the selected granular
drainage materials will be stable on the most critical
slopes (e.g., usually the steepest slope) in the design. 
The calculations and assumptions should be shown, especially
the friction angle between the geomembrane and soil, and if
possible, supported by laboratory and/or field testing
(USEPA, 1988).

     Generally, gravel soil with a group designation of GW
or GP on the Unified Soils Classification Chart can be
expected to have a hydraulic conductivity of greater than
0.01 cm/sec, while sands identified as SW or SP can be
expected to have a coefficient of permeability greater than
0.001 cm/sec.  The sand or gravel drains leachate that
enters the drainage layer to prevent 30 cm (12 in) or more
accumulation on top of the liner during the active life of
the MSWLF unit LCS.  The design of a LCS frequently uses a
drainage material with a hydraulic conductivity of 1 x 10-2
cm/sec or higher.  Drainage materials with hydraulic
conductivities in this order of magnitude should be
evaluated for biological and particulate clogging (USEPA,
1988).  Alternatively, if a geonet is used, the design is
based on the transmissivity of the geonet.

     If a filter layer (soil or geosynthetic) is constructed
on top of a drainage layer to protect it from clogging, and
the LCS is designed and operated to avoid drastic changes in
the oxidation reduction potential of the leachate (thereby
avoiding formation of precipitates within the LCS), then
there is no conceptual basis to anticipate that conductivity
will decrease over time.  Where conductivity is expected to
decrease over time, the change in impingement rate also
should be evaluated over the same time period because the
reduced impingement rate and hydraulic conductivity may
still comply with the 30 cm criterion.

     Unless alternative provisions are made to control
incident precipitation and resulting surface run-off, the
impingement rate during the operating period of the MSWLF
unit is usually at least an order of magnitude greater than
the impingement rate after final closure.  The critical
design condition for meeting the 30 cm (12 in) criterion can
therefore be expected during the operating life.  The
designer may evaluate the sensitivity of a design to meet
the 30 cm (12 in) criterion as a result of changes in
impingement rates, hydraulic conductivity, pipe spacing, and
grades.  Such sensitivity analysis may indicate which
element of the design should be emphasized during
construction quality monitoring or whether the design can be
altered to comply with the 30 cm (12 in) criterion in a more
cost-effective manner.

     The soil material used for the drainage layer should be
investigated at the borrow pit prior to use at the landfill. 
Typical borrow pit characterization testing would include
laboratory hydraulic conductivity and grain size
distribution.  If grain size distribution information from
the borrow pit characterization program can be correlated to
the hydraulic conductivity data, then the grain size test,
which can be conducted in a short time in the field, may be
a useful construction quality control parameter.  Compliance
with this parameter would then be indicative that the
hydraulic conductivity design criterion was achieved in the
constructed drainage layer.  This information could be
incorporated into construction documents after the borrow
pit has been characterized.  If a correlation cannot be made
between hydraulic conductivity and grain size distribution,
then construction documents may rely on direct field or
laboratory measurements to demonstrate that the hydraulic
conductivity design criterion was met in the drainage layer.

     Granular materials are generally placed using
conventional earthmoving equipment, including trucks,
scrapers, bulldozers, and front-end loaders.  Vehicles
should not be driven directly over the geosynthetic membrane
when it is being covered.  (U.S. EPA, 1988a).

     Coarse granular drainage materials, unlike
low-permeability soils, can be placed dry and do not need to
be heavily compacted.  Compacting granular soils tends to
grind the soil particles together, which increases the fine
material and reduces hydraulic conductivity.  To minimize
settlement following material placement, the granular
material may be compacted with a vibratory roller.  The
final thickness of the drainage layer should be checked by
optical survey measurements or by direct test pit
measurements (U.S. EPA, 1988).


     Geosynthetic Drainage Nets 

     Geosynthetic drainage nets (geonets) may be substituted
for the granular layers of the LCRs on the bottom and
sidewalls of the landfill cells.  Geonets require less space
than perforated pipe or gravel and also promote rapid
transmission of liquids.  They do, however, require
geotextile filters above them and can experience problems
with creep and intrusion.  Long-term operating and
performance experience of geonets is limited because the
material and its application are relatively new (U.S. EPA,
1989).

     If a geonet is used in place of a granular drainage
layer, it must provide the same level of performance
(maintaining less than 30 cm of leachate head above the
liner).  An explanation of the calculation used to compute
the capacity of a geonet may be found in U.S. EPA (1987a). 
The transmissivity of a geonet can be reduced significantly
by intrusion of the soil or a geotextile.  A protective
geotextile between the soil and geonet will help alleviate
this concern.  If laboratory transmissivity tests are
performed, they should be done under conditions, loads, and
configurations that closely replicate the actual field
conditions.  It is important that the transmissivity value
used in the leachate collection system design calculations
be selected based upon those loaded conditions (U.S. EPA,
1988).  It is also important to ensure that appropriate
factors of safety are used (Koerner, 1990).

     The flow rate or transmissivity of geonets may be
evaluated by ASTM D-4716.  This flow rate may then be
compared to design-by-function equations presented in U.S.
EPA (1989).  In the ASTM D-4716 flow test, the proposed
collector cross section should be modeled as closely as
possible to actual field conditions (U.S. EPA, 1989).

     Figure 4-7 shows the flow rate "signatures" of a geonet
between two geomembranes (upper curves) and the same geonet
between a layer of clay soil and a geomembrane (lower
curves).  The differences between the two sets of curves
represent intrusion of the geotextile/clay into the
apertures of the geonet.  The curves are used to obtain a
flow rate for the particular geonet being designed (U.S.
EPA, 1989). Equations to determine the design flow rate or
transmissivity are also presented in U.S. EPA (1989), Giroud
(1982), Carroll (1987), Koerner (1990), and FHWA (1987).


************************************************************
                         FIGURE 4-7

             Flow Rate Curves for Geonets in Two
               Composite Liner Configurations
                          [Graphic]
************************************************************


     Generally, geonets perform well and result in high
factors of safety or performance design ratios, unless creep
(elongation under constant stress) becomes a problem or
adjacent materials intrude into apertures (U.S. EPA, 1989). 
For geonets, the most critical specification is the ability
to transmit fluids under load.  The specifications also
should include a minimum transmissivity under expected
landfill operating (dynamic) or completion (static) loads. 
The specifications for thickness and types of material
should be identified on the drawings or in the materials
section of the specifications, and should be consistent with
the design calculations (U.S. EPA, 1988).

     Geonets are often used on the sidewalls of landfills
because of their ease of installation.  They should be
placed with the top ends in a secure anchor trench with the
strongest longitudinal length extending down the slope.  The
geonets need not be seamed to each other on the slopes, only
tied at the edges, butted, or overlapped.  They should be
placed in a loose condition, not stretched or placed in a
configuration where they are bearing their own weight in
tension.  The construction specifications should contain
appropriate installation requirements as described above or
the requirements of the geonet manufacturer.  All geonets
need to be protected by a filter layer or geotextile to
prevent clogging (U.S. EPA, 1988).

     The friction factors against sliding for geotextiles,
geonets, and geomembranes often can be estimated using
manufacturers data because these materials do not exhibit
the range of characteristics as seen in soil materials. 
However, it is important that the designer perform the
actual tests using site materials and that the sliding
stability calculations accurately represent the actual
design configuration, site conditions, and the specified
material characteristics (U.S. EPA, 1988).


Leachate Collection Pipes

     All components of the leachate collection system must
have sufficient strength to support the weight of the
overlying waste, cover system, and post-closure loadings, as
well as the stresses from operating equipment.  The
component that is most vulnerable to compressive strength
failure is the drainage layer piping.  Leachate collection
system piping can fail by excessive deflection, which may
lead to buckling or collapse (USEPA, 1988).  Pipe strength
calculations should include resistance to wall crushing,
pipe deflection, and critical buckling pressure.  Design
equations and information for most pipe types can be
obtained from the major pipe manufacturers.  For more
information regarding pipe structural strength, refer to
U.S. EPA (1988).

     Perforated drainage pipes can provide good long-term
performance.  These pipes have been shown to transmit fluids
rapidly and to maintain good service lives.  The depth of
the drainage layer around the pipe should be deeper than the
diameter of the pipe.  The pipes can be placed in trenches
to provide the extra depth.  In addition, the trench serves
as a sump (low point) for leachate collection.  Pipes can be
susceptible to particulate and biological clogging similar
to the drainage layer material.  Furthermore, pipes also can
be susceptible to deflection.  Proper maintenance and design
of pipe systems can mitigate these effects and provide
systems that function properly.  Acceptable pipe deflections
should be evaluated for the pipe material to be used (USEPA,
1989).

     The design of perforated collection pipes should
consider the following factors:

     *    The required flow using known percolation
          impingement rates and pipe spacing;

     *    Pipe size using required flow and maximum slope;
          and

     *    The structural strength of the pipe.

     The pipe spacing may be determined by the Mound Model. 
In the Mound Model (see Figure 4-8), the maximum height of
fluid between two parallel perforated drainage pipes is
equal to (U.S. EPA, 1989):

                          EQUATION


        where  c         =    q/k
               k         =    permeability
               q         =    inflow rate
               alpha     =    slope.

     The two unknowns in the equation are:

          L    =    distance between the pipes; and 

          c    =    amount of leachate.

     Using a maximum allowable head, h_max, of 30 cm (12
in), the equation is usually solved for "L" (U.S. EPA,
1989).


************************************************************
                         FIGURE 4-8

             Definition of Terms for Mound Model
                   Flow Rate Calculations
                          [Graphic]
************************************************************


     The amount of leachate, "c", can be estimated in a
variety of ways including the Water Balance Method (U.S.
EPA, 1989) and the computer model Hydrologic Evaluation of
Landfill Performance (HELP).  The HELP Model is a
quasi-two-dimensional hydrologic model of water movement
across, into, through, and out of landfills.  The model uses
climatologic, soil, and landfill design data and
incorporates a solution technique that accounts for the
effects of surface storage, run-off, infiltration,
percolation, soil-moisture storage, evapotranspiration, and
lateral drainage.  The program estimates run-off drainage
and leachate that are expected to result from a wide variety
of landfill conditions, including open, partially open, and
closed landfill cells.  The model also may be used to
estimate the depth of leachate above the bottom liner of the
landfill unit.  The results may be used to compare designs
or to aid in the design of leachate collection systems (U.S.
EPA, 1988).

     Once the percolation and pipe spacing are known, the
design flow rate can be obtained using the curve in Figure
4-9. The amount of leachate percolation at the particular
site is located on the x-axis. 


************************************************************
                         FIGURE 4-9

        Required Capacity of Leachate Collection Pipe
                          [Graphic]
************************************************************


     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, the required diameter for the pipe can be
determined (see Figure 4-10).  Finally, the graphs in
Figures 4-11 and 4-12 show two ways to determine whether the
strength of the pipe is adequate for the landfill design. 
In Figure 4-11, the vertical soil pressure is located on the
y-axis.  The density of the backfill material around the
pipe is not governed by strength, so it will deform under
pressure rather than break.  Ten percent is the absolute
limiting deflection value for plastic pipe.  Using Figure
4-11, 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 (U.S. EPA, 1989).


************************************************************
                         FIGURE 4-10

            Leachate Collection Pipe Sizing Chart
                          [Graphic]
************************************************************


************************************************************
                         FIGURE 4-11

   Vertical Ring Deflection Versus Vertical Soil Pressure
          for 18-inch Corrugated Polythethylene in
                   High Pressure Soil Cell
                          [Graphic]
************************************************************


************************************************************
                         FIGURE 4-12

          Example of the Effect of Trench Geometry
             and Pipe Sizing on Ring Deflection
                          [Graphic]
************************************************************


     The LCS specifications should include (U.S. EPA, 1988):

     *    Type of piping material;

     *    Diameter and wall thickness;

     *    Size and distribution of slots and perforations;

     *    Type of coatings (if any) used in the pipe
          manufacturing; and

     *    Type of pipe bedding material and required
          compaction used to support the pipes.

     The construction drawings and specifications should
clearly indicate the type of bedding to be used under the
pipes and the dimensions of any trenches.  The
specifications should indicate how the pipe lengths are
joined.  The drawings should show how the pipes are placed
with respect to the perforations.  To maintain the lowest
possible leachate head, there should be perforations near
the pipe invert, but not directly at the invert.  The pipe
invert itself should be solid to allow for efficient pipe
flow at low volumes (U.S. EPA, 1988).

     When drainage pipe systems are embedded in filter and
drainage layers, no unplugged ends should be allowed.  The
filter materials in contact with the pipes should be
appropriately sized to prevent migration of the material
into the pipe.  The filter media, drainage layer, and pipe
network should be compatible and should represent an
integrated design.


     Protection of Leachate Collection Pipes

     The long-term performance of the LCS depends on the
design used to protect pipes from physical clogging
(sedimentation) by the granular drainage materials.  Use of
a graded material around the pipes is most effective if
accompanied by proper sizing of pipe perforations.  The Army
Corps of Engineers (GCA Corporation, 1983) has established
design criteria using graded filters to prevent physical
clogging of leachate drainage layers and piping by soil
sediment deposits.  When installing graded filters, caution
should be taken to prevent segregation of the material
(USEPA, 1991a).

     Clogging of the pipes and drainage layers of the
leachate collection system can occur through several other
mechanisms, including chemical and biological fouling
(USEPA, 1988).  The LCS should be designed with a cleanout
access capable of reaching all parts of the collection
system with standard pipe cleaning equipment.

     Chemical clogging can occur when dissolved species in
the leachate precipitate in the piping.  Clogging can be
minimized by periodically flushing pipes or by providing a
sufficiently steep slope in the system to allow for high
flow velocities for self-cleansing.  These velocities are
dependent on the diameter of the precipitate particles and
on their specific gravity.  ASCE (1969) discusses these
relationships.  Generally, flow velocities should be in the
range of one or two feet per second to allow for
self-cleansing of the piping (U.S. EPA, 1988).

     Biological clogging due to algae and bacterial growth
can be a serious problem in MSWLF units. There are no
universally effective methods of preventing such biological
growth.  Since organic materials will be present in the
landfill unit, there will be a potential for biological
clogging.  The system design should include features that
allow for pipe system cleanings.  The components of the
cleaning system should include (U.S. EPA, 1991b):

     *    A minimum of six-inch diameter pipes to facilitate
          cleaning;

     *    Access located at major pipe intersections or
          bends to allow for inspections and cleaning; and

     *    Valves, ports, or other appurtenances to introduce
          biocides and/or cleaning solutions.

     In its discussion of drainage layer protection, the
following section includes further information concerning
protection of pipes using filter layers.


     Protection of the High-Permeability Drainage Layer

     The openings in drainage materials, whether holes in
pipes, voids in gravel, or apertures in geonets, must be
protected against clogging by accumulation of fine
(silt-sized) materials.  An intermediate material that has
smaller openings than those of the drainage material can be
used as a filter between the waste and drainage layer.  Sand
may be used as filter material, but has the disadvantage of
taking up vertical space (USEPA, 1989).  Geotextiles do not
use up air space and can be used as filter materials.


     Soil Filter Layers

     There are three parts to an analysis of a sand filter
that is placed above drainage material.  The first
determines whether or not the filter allows adequate flow of
liquids.  The second evaluates whether the void spaces are
small enough to prevent solids from being lost from the
upstream materials.  The third estimates the long-term
clogging behavior of the filter (U.S. EPA, 1989).

     The particle-size distribution of the drainage system
and the particle-size distribution of the invading (or
upstream) soils are required in the design of granular soil
(sand filter) materials.  The filter material should have
its large and small size particles intermediate between the
two extremes.  Equations for adequate flow and retention
are:

          *    Adequate Flow:

               d_85f more than (3 to 5)d_15d.s.

          *    Adequate Retention: 

               d_15f less than (3 to 5)d_85w.f.

     Where     f    =    required filter soil;
               d.s. =    drainage stone; and
               w.f. =    water fines.

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

     The specifications for granular filter layers that
surround perforated pipes and that protect the drainage
layer from clogging are based on a well-defined particle
size distribution.  The orientation and configuration of
filter layers relative to other LCS components should be
shown on all drawings and should be described, with ranges
of particle sizes, in the materials section of the
specifications (U.S. EPA, 1988a).

     Thickness is an important placement criterion for
granular filter material.  Generally, the granular filter
materials will be placed around perforated pipes by hand,
forming an "envelope."  The dimensions of the envelope
should be clearly stated on the drawings or in the
specifications.  This envelope can be placed at the same
time as the granular drainage layer, but it is important
that the filter envelope protect all areas of the pipe where
the clogging potential exists.  The plans and specifications
should indicate the extent of the envelope.  The
construction quality control program should document that
the envelope was installed according to the plans and
specifications (U.S. EPA, 1988).

     A granular filter layer is generally placed using the
same earthmoving equipment as the granular drainage layer. 
The final thickness should be checked by optical survey or
by direct test pit measurement (U.S. EPA, 1988).

     This filter layer is the uppermost layer in the
leachate collection system.  A landfill design option
includes a buffer layer, 12 inches thick (30 cm) or more, to
protect the filter layer and drainage layer from damage due
to traffic.  This final layer can be general fill, as long
as it is no finer than the soil used in the filter layer
(U.S. EPA, 1988).  However, if the layer has a low
permeability, it will affect leachate recirculation
attempts.


     Geotextile Filter Layers

     Geotextile filter fabrics are often used.  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. 
Geotextiles also can be used as cushioning materials above
geomembranes (USEPA, 1989).  Because geotextile filters are
susceptible to biological clogging, their use in areas
inundated by leachate (e.g., sumps, around leachate
collection pipes, and trenches) should be avoided.

     Geotextile filter design parallels sand filter design
with some modifications (U.S. EPA, 1989).  Adequate flow is
assessed by comparing the material (allowable) permittivity
to the design imposed permittivity.  Permittivity is
measured by the ASTM D-4491 test method.  The design
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 (U.S. EPA, 1989):

     DR = theta _allow/theta _reqd

     where:

     theta_allow    =    permittivity from ASTM D-4491

     theta_reqd     =    (q/a) (1/h_max)

     q/a            =    inflow rate per unit area

     h_max          =    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 percent opening size is related to
particles to be retained in the following type of
relationship:

     O_95 less than fct. (d_50, CU, DR)

     where: 

     O_95 =    95% opening size of geotextile;

     d_50 =    50% size of upstream particles;

     CU   =    Uniformity of the upstream particle size; and

     DR   =    Relative density of the upstream particles.

     The O_95 size of a geotextile in the equation is the
opening size at which 5 percent of a given value should be
less than the particle size characteristics of the invading
materials.  In the test for the O_95 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
filter.  The particle-size distribution of retained glass
beads is compared to the allowable value using any of a
number of existing formulas (U.S. EPA, 1989).

     The third consideration in geotextile design is
long-term clogging.  A test method for this problem that may
be adopted by ASTM is called the Gradient Ratio Test.  In
this test, the hydraulic gradient of 1 inch of soil plus the
underlying geotextile is compared with the hydraulic
gradient of 2 inches of soil.  The higher the gradient
ratio, the more likely that a clog will occur.  The final
ASTM gradient ratio test will include failure criteria.  An
alternative to this test method is a long-term flow test
that also is performed in a laboratory.  The test models a
soil-to-fabric system at the anticipated hydraulic gradient. 
The flow rate through the system is monitored.  A long-term
flow rate will gradually decrease until it stops altogether
(U.S. EPA, 1989).

     The primary function of a geotextile is to prevent the
migration of fines into the  leachate pipes while allowing
the passage of leachate.  The most important specifications
are those for hydraulic conductivity and retention.  The
hydraulic conductivity of the geotextile generally should be
at least ten times the soil it is retaining.  An evaluation
of the retention ability for loose soils is based on the 
average particle size of the soil and the apparent opening
size (AOS) of the geotextile.  The maximum apparent opening
size, sometimes called equivalent opening size, is
determined by the size of the soil that will be retained; a
geotextile is then selected to meet that specification.  The
material specifications should contain a range of AOS values
for the geotextile, and these AOS values should match those
used in the design calculations (U.S. EPA, 1988).

     One of the advantages of geotextiles is their light
weight and ease of placement.  The geotextiles are brought
to the site, unrolled, and held down with sandbags until
they are covered with a protective layer.  They are usually
overlapped, not seamed; however, on slopes or in other
configurations, they may be sewn (U.S. EPA, 1988).

     As with granular filter layers, it is important that
the design drawings be clear in their designation of
geotextile placement so that no potential route of pipe or
drainage layer clogging is left unprotected.  If geotextiles
are used on a slope, they should be secured in an anchor
trench similar to those for geomembranes or geonets (U.S.
EPA, 1988).


Leachate Removal System

     Sumps, located in a recess at the low point(s) within
the leachate collection drainage layer, provide one method
for leachate removal from the MSWLF unit.  In the past, low
volume sumps have been constructed successfully from
reinforced concrete pipe on a concrete footing, and
supported above the geomembrane on a steel plate to protect
the geomembrane from puncture.  Recently, however,
prefabricated polyethylene structures have become available. 
These structures may be suitable for replacing the concrete
components of the sump and have the advantage of being
lighter in weight.

     These sumps typically house a submersible pump, which
is positioned close to the sump floor to pump the leachate
and to maintain a 30 cm (12 in) maximum leachate depth. 
Low-volume sumps, however, can present operational problems. 
Because they may run dry frequently, there is an increased
probability of the submersible pumps burning out.  For this
reason, some landfill operators prefer to have sumps placed
at depths between 1.0 and 1.5 meters.  While head levels of
30 cm or less are to be maintained on the liner, higher
levels are acceptable in sumps.  Alternatively, the sump may
be designed with level controls and with a backup pump to
control initiation and shut-off of the pumping sequence and
to have the capability of alternating between the two pumps. 
The second pump also may be used in conjunction with the
primary pump during periods of high flow (e.g., following
storm events) and as a backup if the primary pump fails to
function.  A visible alarm warning light to indicate pump
failure to the operator also may be installed.

     Pumps used to remove leachate from the sumps should be
sized to ensure removal of leachate at the maximum rate of
generation.  These pumps also should have a sufficient
operating head to lift the leachate to the required height
from the sump to the access port.  Portable vacuum pumps can
be used if the required lift height is within the limit of
the pump.  They can be moved in sequence from one leachate
sump to another.  The type of pump specified and the
leachate sump access pipes should be compatible and should
consider performance needs under operating and closure
conditions (U.S. EPA, 1988).

     Alternative methods of leachate removal include
internal standpipes and pipe penetrations through the
geomembrane, both of which allow leachate removal by gravity
flow to either a leachate pond or exterior pump station.  If
a leachate removal standpipe is used, it should be extended
through the entire landfill from liner to cover and then
through the cover itself.  If a gravity drainage pipe that
requires geomembrane penetration is used, a high degree of
care should be exercised in both the design and construction
of the penetration.  The penetration should be designed and
constructed in a manner that allows nondestructive quality
control testing of 100 percent of the seal between the pipe
and the geomembrane.  If not properly constructed and
fabricated, geomembrane penetrations can become a source of
leakage through the geomembrane.


     Other Design Considerations

     The stability of the individual leachate collection
system components placed on geomembrane-covered slopes
should be considered.  A method for calculating the factor
of safety (FS) against sliding for soils placed on a sloped
geomembrane surface is provided in Koerner (1990).  This
method considers the factors affecting the system, including
the slope length, the slope angle, and the friction angle
between the geomembrane and its cover soil.  Generally, the
slope angle is known and is specified on the design
drawings.  A minimum FS is then selected.  From the slope
angle and the FS, a minimum allowable friction angle is
determined, and the various components of the liner system
are selected based on this minimum friction angle.  If the
design evaluation results in an unacceptably low FS, then
either the sidewall slope or the materials should be changed
to produce an adequate design (U.S. EPA, 1988).  For short
slopes in a landfill unit, the FS can be as low as 1.1 to
1.2 if the slope will be unsupported (i.e., no waste will be
filled against it) for only a short time, and if any
failures that do occur can be repaired fairly easily. 
Longer slopes may require higher factors of safety due to
the potential of sliding material to tear the geomembrane
along the slope or near the toe of the slope.


Construction Quality Assurance and Quality Control

     The following section is excerpted from U.S. EPA
(1992).  This section discusses quality assurance and
quality control (QA/QC) objectives.  For a more detailed
discussion on QA/QC and specific considerations, refer to
U.S. EPA (1992).


     CQA/CQC Objectives

     Construction quality assurance (CQA) consists of a
planned series of observations and tests to ensure that the
final product meets project specifications.  CQA plans,
specifications, observations, and tests are used to provide
quantitative criteria with which to accept the final
product.

     On routine construction projects, CQA is normally the
concern of the owner and is obtained using an independent
third-party testing firm.  The independence of the
third-party inspection firm is important, particularly when
the owner is a corporation or other legal entity that has
under its corporate "umbrella" the capacity to perform the
CQA activities.  Although "in-house" CQA personnel may be
registered professional engineers, a perception of
misrepresentation may exist if CQA is not performed by an
independent third party.

     The CQA officer should fully disclose any activities or
relationships with the owner that may impact his
impartiality or objectivity.  If such activities or
relationships exist, the CQA officer should describe actions
that have been or can be taken to avoid, mitigate, or
neutralize the possibility they might affect the CQA
officer's objectivity.  Regulatory representatives can then
evaluate whether these mechanisms are sufficient to ensure
an acceptable CQA product.

     Construction quality control (CQC) is an on-going
process of measuring and controlling the characteristics of
the product in order to meet manufacturer's or project
specifications.  CQC is a production tool that is employed
by the manufacturer of materials and by the contractor
installing the materials at the site.  CQA, by contrast, is
a verification tool employed by the facility owner or
regulatory agency to ensure that the materials and
installations meet project specifications.  CQC is performed
independently of the CQA Plan.  For example, while a
geomembrane liner installer will perform CQC testing of
field seams, the CQA program will require independent CQA
testing of those same seams by a third-party inspector.

     The CQA/CQC plans are implemented through inspection
activities that include visual observations, field testing
and measurements, laboratory testing, and evaluation of the
test data.  Inspection activities typically are concerned
with four separate functions:

     *    Quality Control (QC) Inspection by the
          Manufacturer provides an in-process measure of the
          product quality and its conformance with the
          project plans and specifications.  Typically, the
          manufacturer will QC test results to certify that
          the product conforms to project plans and
          specifications.

     *    Construction Quality Control (CQC) Inspection by
          the Contractor provides an in-process measure of
          construction quality and conformance with the
          project plans and specifications, thereby allowing
          the contractor to correct the construction process
          if the quality of the product is not meeting the
          specifications and plans.

     *    Construction Quality Assurance (CQA) Testing by
          the Owner (Acceptance Inspection) performed by the
          owner usually through the third-party testing
          firm, provides a measure of the final product
          quality and its conformance with project plans and
          specifications.  Due to the size and costs of a
          typical MSWLF unit construction project, rejection
          of the project at completion would be costly to
          all parties.  Acceptance Inspections as portions
          of the project become complete allow deficiencies
          to be found and corrected before they become too
          large and costly.

     *    Regulatory Inspection often is performed by a
          regulatory agency to ensure that the final product
          conforms with all applicable codes and
          regulations.  In some cases, the regulatory agency
          will use CQA documentation and the as-built plans
          or "record drawings" to confirm compliance with
          the regulations.


Soil Liner Quality Assurance/Quality Control

     Quality control testing performed on materials used in
construction of the landfill unit includes source testing
and construction testing.  Source testing defines material
properties that govern material placement.  Source testing
commonly includes moisture content, soil density, Atterberg
limits, grain size, and laboratory hydraulic conductivity. 
Construction testing ensures that landfill construction has
been performed in accordance with the plans and technical
specifications.  Construction testing generally includes
tests of soil moisture content, density, lift thickness, and
hydraulic conductivity. 

     The method of determining compliance with the maximum
hydraulic conductivity criterion should be specified in the
QA/QC plan.  Some methods have included the use of the
criterion as a maximum value that never should be exceeded,
while other methods have used statistical techniques to
estimate the true mean.  The sample collection program
should be designed to work with the method of compliance
determination.  Selection of sample collection points should
be made on a random basis.

     Thin wall sampling tubes generally are used to collect
compacted clay samples for laboratory hydraulic conductivity
testing.  It is important to minimize disturbance of the
sample being collected.  Tubes pushed into the soil by a
backhoe may yield disturbed samples.  A recommended
procedure (when a backhoe is available during sample
collection) is to use the backhoe bucket as a stationary
support and push the tube into the clay with a jack
positioned between the clay and the tube.  The sample hole
should be filled with bentonite or a bentonite clay mixture,
and compacted using short lifts of material.  

     If geophysical methods are used for moisture and
density measurements, it is recommended that alternative
methods be used less frequently to verify the accuracy of
the faster geophysical methods.  Additional information on
testing procedures can be found in U.S. EPA (1988b) and U.S.
EPA (1990a). 

     Quality assurance testing for soil liners includes the
same testing requirements as specified above for control
testing.  Generally, the tests are performed less frequently
and are performed by an individual or an entity independent
of the contractor.  Activities of the construction quality
assurance (CQA) officer are essential to document quality of
construction.  The CQA officer's responsibilities and those
of the CQA officer's staff members may include:

     *    Communicating with the contractor;

     *    Interpreting and clarifying project drawings and
          specifications with the designer, owner, and
          contractor;

     *    Recommending acceptance or rejection by the
          owner/operator of work completed by the
          construction contractor;

     *    Submitting blind samples (e.g., duplicates and
          blanks) for analysis by the contractor's testing
          staff or one or more independent laboratories, as
          applicable;

     *    Notifying owner or operator of construction
          quality problems not resolved on-site in a timely
          manner;

     *    Observing the testing equipment, personnel, and
          procedures used by the construction contractor to
          check for detrimentally significant changes over
          time;

     *    Reviewing the construction contractor's quality
          control recording, maintenance, summary, and
          interpretations of test data for accuracy and
          appropriateness; and

     *    Reporting to the owner/operator on monitoring
          results.


Soil Liner Pilot Construction (Test Fill)

     A pilot construction or test fill is a small-scale test
pad that can be used to verify that the soil, equipment, and
construction procedures can produce a liner that performs
according to the construction drawings and specifications. 
An owner or operator may want to consider the option of
constructing a test fill prior to the construction of the
liner.  A test pad is useful not only in teaching people how
to build a soil liner, it also can function as a
construction quality assurance tool.  If the variables used
to build a test pad that achieves a 1x10^-7 cm/sec hydraulic
conductivity are followed exactly, then the completed
full-size liner should meet the regulatory requirements
(U.S. EPA, 1989).  A test fill may be a cost-effective
method for the contractor to evaluate the construction
methods and borrow source.  Specific factors that can be
examined/tested during construction of a test fill include
(U.S. EPA, 1988b):

     *    Preparation and compaction of foundation material
          to the required bearing strength;

     *    Methods of controlling uniformity of the soil
          material;

     *    Compactive effort (e.g., type of equipment, number
          of passes) to achieve required soil density and
          hydraulic conductivity;

     *    Lift thickness and placement procedures to achieve
          uniformity of density throughout a lift and the
          absence of apparent boundary effects between lifts
          or between placements in the same lift;

     *    Procedures for protecting against desiccation
          cracking or other site- and season-specific
          failure mechanisms for the finished liner or
          intermediate lifts;

     *    Measuring the hydraulic conductivity on the test
          fill in the field and collecting samples of
          field-compacted soil for laboratory testing;

     *    Test procedures for controlling the quality of
          construction;

     *    Ability of different types of soil to meet
          hydraulic conductivity requirements in the field;
          and

     *    Skill and competence of the construction team,
          including equipment operators and quality control
          specialists.


Geomembrane Quality Assurance/Quality Control Testing

     As with the construction of soil liners, installation
of geomembrane liners should be in conformance with a
quality assurance/quality control plan.  Tests performed to
evaluate the integrity of geomembrane seams are generally
considered to be either "destructive" or "non-destructive."


     Destructive Testing

     Quality control testing of geomembranes generally
includes peel and shear testing of scrap test weld sections
prior to commencing seaming activities and at periodic
intervals throughout the day.  Additionally, destructive
peel and shear field tests are performed on samples from the
installed seams.

     Quality assurance testing generally requires that an
independent laboratory perform peel and shear tests of
samples from installed seams.  The samples may be collected
randomly or in areas of suspect quality.  HDPE seams are
generally tested at intervals equivalent to one sample per
every 300 to 400 feet of installed seam for extrusion welds,
and every 500 feet for fusion-welded seams.  Extrusion seams
on HDPE require grinding prior to welding, which can greatly
diminish parent material strengths if excessive grinding
occurs.  Detailed discussion of polyethylene welding
protocol can be found in U.S. EPA (1991a).  For dual hot
wedge seams in HDPE, both the inner and outer seam may be
subjected to destructive shear tests at the independent
laboratory.  Destructive samples of installed seam welds are
generally cut into several pieces and distributed to:

     *    The installer to perform construction quality
          control field testing;

     *    The owner/operator to retain and appropriately
          catalog or archive; and

     *    An independent laboratory for peel and shear
          testing. 

     If the test results for a seam sample do not pass the
acceptance/rejection criteria, then samples are cut from the
same field seam on both sides of the rejected sample
location.  Samples are collected and tested until the areal
limits of the low quality seam are defined.  Corrective
measures should be undertaken to repair the length of seam
that has not passed the acceptance/rejection criteria.  In
many cases, this involves seaming a cap over the length of
the rejected seam or reseaming the affected area (U.S. EPA,
1988).  In situations where the seams continually fail
testing, the seaming crews may have to be retrained.


     Non-Destructive Testing

     Non-destructive test methods are conducted in the field
on an in-place geomembrane.  These test methods determine
the integrity of the geomembrane field seams. 
Non-destructive test methods include the probe test, air
lance, vacuum box, ultrasonic methods (pulse echo, shadow
and impedance plane), electrical spark test, pressurized
dual seam, electrical resistivity, and hydrostatic tests. 
Detailed discussion of these test methods may be found in
U.S. EPA (1991a).  Seam sections that fail appropriate,
non-destructive tests must be carefully delineated, patched
or reseamed, and retested.  Large patches or reseamed areas
should be subjected to destructive test procedures for
quality assurance purposes.  The specifications should
clearly describe the degree to which non-destructive and
destructive test methods will be used in evaluating failed
portions of non-destructive seam tests.


Geomembrane Construction Quality Assurance Activities

     The responsibilities of the construction quality
assurance (CQA) personnel for the installation of the
geomembrane are generally the same as the responsibilities
for the construction of a soil liner with the following
additions:

     *    Observation of liner storage area and liners in
          storage, and handling of the liner as the panels
          are positioned in the cell;

     *    Observation of seam overlap, seam preparation
          prior to seaming, and material underlying the
          liner;

     *    Observation of destructive testing conducted on
          scrap test welds prior to seaming;

     *    Observation of destructive seam sampling,
          submission of the samples to an independent
          testing laboratory, and review of results for
          conformance to specifications;

     *    Observation of all seams and panels for defects
          due to manufacturing and/or handling and
          placement;

     *    Observation of all pipe penetration boots and
          welds in the liner;

     *    Preparation of reports indicating sampling
          conducted and sampling results, locations of
          destructive samples, locations of patches,
          locations of seams constructed, and any problems
          encountered; and,

     *    Preparation of record drawings of the liner
          installation, in some cases.

     The last responsibility is frequently assigned to the
contractor, the owner's representative, or the engineer.


Leachate Collection System Construction Quality Assurance

     The purpose of leachate collection system CQA is to
document that the system construction is in accordance with
the design specifications.  Prior to construction, all
materials should be inspected to confirm that they meet the
construction plans and specifications.  These include (U.S.
EPA, 1988):

     *    Geonets;

     *    Geotextiles;

     *    Pipe size, materials, and perforations;

     *    Granular material gradation and prefabricated
          structures (sumps, manholes, etc.);

     *    Mechanical, electrical, and monitoring equipment;
          and

     *    Concrete forms and reinforcement.

     The leachate collection system foundation (geomembrane
or low permeability soil liner) should be inspected and
surveyed upon its completion to ensure that it has proper
grading and is free of debris and liquids (U.S. EPA, 1988).

     During construction, the following activities, as
appropriate, should be observed and documented (U.S. EPA,
1988):

     *    Pipe bedding placement including quality,
          thickness, and areal coverage;

     *    Granular filter layer placement including material
          quality and thickness;

     *    Pipe installation including location,
          configuration, grades, joints, filter layer
          placement, and final flushing;

     *    Granular drainage layer placement including
          protection of underlying liners, thickness,
          overlap with filter fabrics and geonets if
          applicable, and weather conditions;

     *    Geonet placement including layout, overlap, and
          protection from clogging by granular material
          carried by wind or run-off during construction;

     *    Geotextile/geofabric placement including coverage
          and overlap;

     *    Sumps and structure installation; and

     *    Mechanical and electrical equipment installation
          including testing.

     In addition to field observations, actual field and
laboratory testing may be performed to document that the
materials meet the design specifications.  These activities
should be documented and should include the following (U.S.
EPA, 1988):

     *    Geonet and geotextile sampling and testing;

     *    Granular drainage and filter layer sampling and
          testing for grain size distribution; and

     *    Testing of pipes for leaks, obstructions, and
          alignments.

     Upon completion of construction, each component should
be inspected to identify any damage that may have occurred
during its installation, or during construction of another
component (e.g., pipe crushing during placement of granular
drainage layer).  Any damage that does occur should be
repaired, and these corrective measures should be documented
in the CQA records (U.S. EPA, 1988).

     
4.4  RELEVANT POINT OF COMPLIANCE 40 CFR Section 258.40(d)

     4.4.1     Statement of Regulation

     (a) (See Statement of Regulation in Section 4.2.1 of
this guidance document for the regulatory language for
performance-based design requirements.) 

     (b) (See Statement of Regulation in Section 4.3.1 of
this guidance document for the regulatory language for
requirements pertaining to composite liner and leachate
collection systems.) 

     (c) (See Statement of Regulation in Section 4.2.1 of
this guidance document for the regulatory language for
performance-based design requirements.) 

     (d) The relevant point of compliance specified by the
Director of an approved State shall be no more than 150
meters from the waste management unit boundary and shall be
located on land Owned by the owner of the MSWLF unit.  
In determining the relevant point of compliance, the State
Director shall consider at least the following factors:

     (1) The hydrogeologic characteristics of the facility
and surrounding land;

     (2) The volume and physical and chemical
characteristics of the leachate;

     (3) The quantity, quality, and direction of flow of
ground water;

     (4) The proximity and withdrawal rate of the
ground-water users;

     (5) The availability of alternative drinking water
supplies;

     (6) The existing quality of the ground water, including
other sources of contamination and their cumulative impacts
on the ground water and whether the ground water is
currently used or reasonably expected to be used for
drinking water;

     (7) Public health, safety, and welfare effects; and

     (8) Practicable capability of the owner or operator.


     4.4.2     Applicability

     In States with approved permit programs, owners/
operators may have the opportunity to employ an alternative
liner design, as per Section 258.40(a)(1).  In these
situations, some flexibility is allowed in terms of
establishing a relevant point of compliance.  The relevant
point of compliance may be located a maximum of 150 meters
from the waste management unit boundary; however, the
location must be on property owned by the MSWLF unit owner
or operator.

     In unapproved States the relevant point of compliance
is set at the waste management unit boundary.  The waste
management unit boundary is defined as the vertical surface
located at the hydraulically downgradient limit of the unit. 
This vertical surface extends down into and through the
entire thickness of the uppermost aquifer.


     4.4.3     Technical Considerations

     At least eight factors should be considered in
establishing the relevant point of compliance for any design
under Section 258.40.  The factors provide information
needed to determine if the alternative boundary is
sufficiently protective of human health and the environment
and if the relevant point of compliance is adequate to
measure the performance of the disposal unit.


Site Hydrogeology

     The first factor to be considered when determining the
relevant point of compliance is site hydrogeology.  Site
hydrogeologic characteristics should be used to identify
additional information required to set the relevant point of
compliance.  The site data should be sufficient to determine
the lateral well-spacing required to detect contaminant
releases to the uppermost aquifer.  Hydrogeologic
information required to fully characterize a site is
presented in greater detail in Section 5.6.3.


Leachate Volume and Physical Characteristics

     Data on leachate volume and quality are needed to make
a determination of the "detectability" of leakage from the
facility at the relevant point of compliance.  The net
concentration at any given point resulting from the
transport of contaminants from the landfill is a function of
contaminant type, initial contaminant concentration, and
leakage rate.  Assessment of leachate volume is discussed in
Sections 4.2 and 4.3.  The assessment of contaminant fate
and transport was discussed in Section 4.3.  


Quality, Quantity and Direction of Ground-Water Flow

     The hydrogeologic data collected should provide
information to assess the ground-water flow rate,
ground-water flow direction, and the volume of ground-water
flow.  Background ground-water quality data should be used
to establish baseline concentrations of the monitoring
constituents.  This information will be required as input to
determine if contaminants from the landfill unit have been
released and have migrated to the relevant point of
compliance.


Ground-Water Receptors

     The goal of establishing the relevant point of
compliance is to ensure early detection of contamination of
the uppermost aquifer.  The distance to the relevant point
of compliance should allow sufficient time for corrective
measures to be implemented prior to the migration of
contaminants to private or public water supply wells.

     Existing users of ground water immediately downgradient
from the facility should be identified on a map.  Users
located at a downgradient point where contaminants might be
expected to migrate during the active life and post-closure
care period of the facility should be identified.


Alternative Drinking Water Supplies

     Consideration should be given to the availability of
alternate drinking water supplies in the event of a
ground-water contamination problem.  If the uppermost
aquifer is the sole water supply source available, all
reasonable efforts should be made to locate the relevant
point of compliance as close as possible to the actual waste
management unit boundary.


Existing Ground-Water Quality

     The existing ground-water quality, both upgradient and
downgradient of the MSWLF unit, should be determined prior
to establishing the relevant point of compliance (see
Section 5.6.3).  The performance standard for landfill
design requires that landfill units be designed so that the
concentrations listed in Table 1 are not exceeded at a
relevant point of compliance.  Issues for approved States to
consider are whether the ground water is currently used or
is reasonably expected to be used as a drinking water source
when setting a relevant point of compliance.  If the ground
water is not currently or reasonably expected to be used for
drinking water, the State may allow the relevant point of
compliance to be set near the 150-meter limit.


Public Health, Welfare, Safety

     Consideration should be given to the potential overall
effect on public health, welfare, and safety of the proposed
relevant point of compliance.  Issues that should be
considered include:

     *    Distance to the nearest ground-water user or
          potentially affected surface water;

     *    The response time (based on the distance to the
          proposed relevant point of compliance) required to
          identify and remediate or otherwise contain ground
          water that may become impacted and potentially
          affect downgradient water supplies; and 

     *    The risk that detection monitoring data may not be
          representative of a worst case release of
          contaminants to ground water.


Practicable Capability of the Owner or Operator

     If the relevant point of compliance is placed farther
from the waste management unit boundary, the volume of water
requiring treatment, should the ground water become
contaminated, will increase.  One or more of the following
conditions could affect the owner's or operator's
practicable capability (technical and financial) to
remediate contaminant releases:

     *    Area of impact, remedial costs, scope of remedial
          investigation, and site characterization;

     *    Increased response time due to higher costs and
          increased technical scope of selected remedial
          method;

     *    A reduction of the removal efficiency of treatment
          technologies; and

     *    Increased difficulty in ground-water extraction or
          containment if these technologies are chosen.

     The Director may require some indication of financial
capability of the owner or operator to maintain a longer and
more costly remedial program due to the longer detection
time frame associated with a relevant point of compliance
located at a greater distance from the waste management unit
boundary.  Additional information on remedial actions for
ground water is provided in this document in Chapter 5.

     
4.5  PETITION PROCESS 40 CFR Section 258.40(e)

     4.5.1     Statement of Regulation

     (a) - (d) (See Statement of Regulation in Sections
4.2.1, 4.3.1, and 4.4.1 of this guidance document for
regulatory  language.)

     (e) If EPA does not promulgate a rule establishing the
procedures and requirements for State compliance with RCRA 
Section 4005(c)(1)(B) by October 9, 1993, owners and
operators in unapproved States may utilize a design meeting
the performance standard in Secction 258.40(a)(1) if the
following conditions are met:

     (1) The State determines the design meets the
performance standard in Section 258.40(a)(1);

     (2) The State petitions EPA to review its
determination; and

     (3) EPA approves the State determination or does not
disapprove the determination within 30 days.

     [Note to Subpart D:  40 CFR Part 239 is reserved to
establish the procedures and requirements for State
compliance with RCRA Section 4005(c)(1)(B).]


     4.5.2     Applicability

     If EPA does not promulgate procedures and requirements
for state approval by October 9, 1993, owners and operators
of MSWLF units located in unapproved States may be able to
use an alternative design (in compliance with Section
258.40(a)(1)) under certain circumstances.

     Owners or operators of MSWLF units should contact the
municipal solid waste regulatory department in their State
to determine if their State has been approved by the U.S.
EPA.


4.6  FURTHER INFORMATION

     4.6.1     References

(Specific to Performance-Based Design Assessment and Solute
Transport Modeling)

Abriola, L.M., and G.F. Pinder, (1985a).  A Multiphase
Approach to the Modeling of Porous Media Contamination by
Organic Compounds 1. Equation Development. Water Resources
Research 21(1):11-18.

Abriola, L.M., and G.F. Pinder, (1985b).  A Multiphase
Approach to the Modeling of Porous Media Contamination by
Organic Compounds 2. Numerical Simulation. Water Resources
Research 21(1):19-26.

Aller, L., T. Bennett, J.H. Lehr, R.J. Petty, and G.
Hackett, (1987).  DRASTIC: A Standardized System for
Evaluation Ground Water Pollution Potential Using
Hydrogeologic Settings.  EPA-600/2-87-035, Kerr
Environmental Research Lab, U.S. Environmental Protection
Agency, Ada, Oklahoma.  455 pp.

Auerbach, S.I., C. Andrews, D. Eyman, D.D. Huff, P.A.
Palmer, and W.R. Uhte, (1984).  Report of the Panel on Land
Disposal.  In: Disposal of Industrial and Domestic Wastes:
Land and Sea Alternatives.  National Research Council.
National Academy Press.  Washington, DC.  pp. 73-100.

Beljin, M.S., (1985).  A Program Package of Analytical
Models for Solute Transport in Groundwater "SOLUTE".  BAS15,
International Groundwater Modeling Center, Holcomb Research
Institute, Butler University, Indianapolis, Indiana. 163 pp. 

Bond, F., and S. Hwang, (1988).  Selection Criteria for
Mathematical Models Used in Exposure Assessments: 
Groundwater Models.  EPA/600/8-88/075, U.S. Environmental
Protection Agency, Washington, DC.

Boutwell, S.H., S.M. Brown, B.R. Roberts, and D.F. Atwood,
(1986).  Modeling Remedial Actions at Uncontrolled Hazardous
Waste Sites.  EPA/540/2-85/001, U.S. Environmental
Protection Agency, Athens, Georgia.

Cederberg, G.A., R.L. Street, and J.O. Leckie, (1985).  A
Groundwater Mass Transport and Equilibrium Chemistry Model
for Multicomponent Systems. Water Resources Research,
21(8):1095-1104.

Dean, J.D., P.S. Huyakorn, A.S. Donigian, Jr., K.S. Voos,
R.W. Schanz, Y.J.Meeks, and R.F. Carsel, (1989).  Risk of
Unsaturated/Saturated Transport and Transformation of
Chemical Concentrations (RUSTIC).  EPA/600/3-89/048a, U.S.
EPA, Athens, Georgia.  

de Marsily, G., (1986).  Quantitative Hydrogeology: 
Groundwater Hydrology for Engineers. Academic Press, San
Diego, California.  440 pp.

Dillon, R.T., R.M. Cranwell, R.B. Lantz, S.B. Pahwa, and
D.S. Ward, (1978).  Risk Methodology for Geologic Disposal
of Radioactive Waste:  The Sandia Waste Isolation Flow and
Transport (SWIFT) model.  Sand 78-1267/NUREG-CR-0424, Sandia
national Laboratories, Albuquerque, New Mexico.

Domenico, P.A., and V.V. Palciauskas, (1982).  Alternative
Boundaries in Solid Waste Management.  Ground Water,
20(3):303-311.

Domenico, P.A., and G.A. Robbins, (1985).  A New Method for
Contaminant Plume Analysis.  Ground Water, 23(4):476-485.

Donigian, A.S., and P.S.C. Rao, (1990).  Selection,
Application, and Validation of Environmental Models.  In:
Proceedings of the International Symposium on Water Quality
Modeling of Agricultural Non-Point Sources, Part 2.  D.G.
DeCoursey (ed.).  ARS-81, U.S. Department of Agriculture
Agricultural Research Services.  pp. 577-600.

Erdogen, H., and R.D. Heufeld, (1983).  Modeling Leachates
at Landfill Boundaries. Journal of Environmental
Engineering, 109(5):1181-1194.

Faust, C.R., J.H. Guswa, and J.W. Mercer, (1989). 
Simulation of Three-Dimensional Flow of Immiscible Fluids
Within and Below the Unsaturated Zone.  Water Resources
Research, 25(12):2449-2464.

Freeze, R.A., and J.A. Cherry, (1979).  Ground Water. 
Prentice-Hall, Englewood Cliffs, New Jersey.  604 pp.

GeoTrans, Inc., (1985).  SWANFLOW: Simultaneous Water, Air
and Non-Aqueous Phase Flow, Version 1.0-Code Documentation. 
Herndon, Virginia.  97 pp.

Grove, D.B., and K.G. Stollenwerk, (1987).  Chemical
Reactions Simulated by Groundwater Quality Models.  Water
Resources Bulletin, 23(4):601-615.

Gupta, S.K., C.R. Cole, C.T. Kincaid, and F.E. Kaszeta,
(1982).  Description and Applications of the FE3DGW and
CFEST Three-dimensional Finite Element Models, Battelle
Pacific NW Laboratories, Richland, Washington.

Gupta, S.K., C.T. Kincaid, P. Meyer, C. Newbill, and C.R.
Cole, (1982).  CFEST: Multidimensional Finite Element Code
for the Analysis of Coupled Fluid, Energy and Solute
Transport.  PNL-4260, Battelle Pacific NW Laboratories,
Richland, Washington.

Gureghian, A.B., D.S. Ward, and R.W. Cleary, (1980).  A
Finite Element Model for the Migration of Leachate from a
Sanitary Landfill in Long Island, New York - Part I: 
Theory.  Water Resources Bulletin, 16(5):900-906.

Guvanasen, V., (1984).  Development of A Finite Element Code
and Its Application to Geoscience Research.  Proceedings
17th Information Meeting of the Nuclear Fuel Waste
Management Program, Atomic Energy of Canada, Ltd. Technical
Record TR-199.  pp. 554-566.

Haji-Djafari, S., (1983).  User's Manual GEOFLOW Groundwater
Flow and Mass Transport Computer Program.  D'Appolonia,
Pittsburgh, Pennsylvania.

Huyakorn, P.S. et al., (1984).  Testing and Validation of
Models for Simulating Solute Transport in Groundwater:
Development, Evaluation and Comparison of Benchmark
Techniques.  GWMI 84-13, International Groundwater Modeling
Center, Holcomb Research Institute, Indianapolis, Indiana.

Huyakorn, P.S., M.J. Ungs, L.A. Mulkey, and E.A. Sudicky,
(1987).  A Three-Dimensional Analytical Method for
Predicting Leachate Migration.  Ground Water, 25(5):588-598.

Huyakorn, P.S., H.O. White, Jr., V.M. Guvanasen, and B.H.
Lester, (1986). TRAFRAP:  A Two-dimensional Finite Element
Code for Simulating Fluid Flow and Transport of
Radionuclides in Fractured Porous Media.  FOS-33,
International Groundwater Modeling Center, Holcomb Research
Institute, Butler University, Indianapolis, Indiana.

Javandel, I., C. Doughty, and C.F. Tsang, (1984). 
Groundwater Transport: Handbook of Mathematical Models. 
Water Resources Monogram 10, American Geophysical Union,
Washington, DC  228 pp.

Keely, J.F., (1987).  The Use of Models in Managing
Ground-Water Protection Programs.  U.S. Environmental
Protection Agency.  EPA/600/8-87/003, Ada, Oklahoma.  72 pp.

Keely, J.F., (1989).  Performance Evaluations of
Pump-and-Treat Remediations. EPA/540/4-89/005, U.S.
Environmental Protection Agency, Ada, Oklahoma. 19 pp.

Kincaid, C.T., J.R. Morrey, and J.E. Rogers, (1984a). 
Geohydrochemical Models for Solute Migration- Volume 1:
Process Description and Computer Code Selection.  EA-3417,
Electric Power Research Institute, Palo Alto, California.  

Kincaid, C.T., J.R. Morrey, S.B. Yabusaki, A.R. Felmy, and
J.E. Rogers, (1984b). Geohydrochemical Models for Solute
Migration- Volume 2: Preliminary Evaluation of Selected
Computer Codes.  EA-3417, Electric Power Research Institute,
Palo Alto, California.  


Kipp, K.L., Jr., (1987).  HST3D: A Computer Code for
Simulation of Heat and Solute Transport in Three-Dimensional
Groundwater Flow Systems.  WRI 86-4095, U.S. Geological
Survey, Lakewood, Colorado.

Konikow, L.F., and J.D. Bredehoeft, (1985). 
Method-of-Characteristics Model for Solute Transport (1985
revision).  U.S. Geological Survey.

Lindstrom, F.T., and L. Boersma, (1989).  Analytical
Solutions for Convective-Dispersive Transport in Confined
Aquifers with Different Initial and Boundary Conditions. 
Water Resources Research, 25(2):241-256.

Lu, J.C.S., B. Eichenberger, and R.J. Stearns, (1985). 
Leachate Migration from Municipal Landfills.  Pollution
Technology Review No. 19.  Noyes Publications, Park Ridge,
New Jersey.  453 pp.

Mercer, J.W., S.D. Thomas, and B. Ross, (1983).  Parameters
and Variables Appearing in Repository Siting Models. 
NUREG/CR-3066.  Prepared for U.S. Nuclear Regulatory
Commission, Washington, DC.  244 pp.

Mulkey, L.A., A.S. Donigian, Jr., T.L. Allison, and C.S.
Raju, (1989).  Evaluation of Source Term Initial Conditions
for Modeling Leachate Migration from Landfills.  U.S. EPA,
Athens, Georgia.

Narasimhan, T.N., A.F. White, and T. Tokunaga.  1986. 
Groundwater Contamination From an Inactive Uranium Mill
Tailings Pile  2.  Application of a Dynamic Mixing Model. 
Water Resources Research, 22(13):1820-1834.

National Research Council, (1990).  Ground Water Models: 
Scientific and Regulatory Applications.  National Academy
Press, Washington, DC.  320 pp.

Nelson, R.W., and J.A. Schur, (1980).  PATHS Groundwater
Hydrologic Model.  PNL-3162, Battelle Pacific NW
Laboratories, Richland, Washington. 

Osborne, M., and J. Sykes, (1986).  Numerical Modeling of
Immiscible Organic Transport at the Hyde Park Landfill. 
Water Resources Research, 22(1):25-33.

Ostendorf, D.W., R.R. Noss, and D.O. Lederer, (1984). 
Landfill Leachate Migration through Shallow Unconfined
Aquifers, Water Resources Research, 20(2):291-296.

Oster, P.A.  Review of Ground-Water Flow and Transport
Models in the Unsaturated Zone, (1982).  NUREG/CR-2917,
PNL-4427.  Pacific Northwest Laboratory, Richland,
Washington.
 
Prakash, A., (1984).  Groundwater Contamination Due to
Transient Sources of Pollution.  J. of Hydraulic
Engineering, 110(11):1642-1658.

Prickett, T.A., T.G. Naymik, and C.G. Lonnquist, (1981).  A
Random-Walk Solute Transport Model for Selected Groundwater
Quality Evaluations.  Bulletin 65, Illinois State Water
Survey, Champaign, Illinois.

Runchal, A.K., (1985).  PORFLOW: A General Purpose Model for
Fluid Flow, Heat Transfer and Mass Transport in Anisotropic,
Inhomogeneous, Equivalent Porous Media, Volume I: Theory,
Volume II: User's Manual.  ACRI/TN-O11. Analytic and
Computational Research, Inc.  West Los Angeles, California.

Runchal, A.K., (1985).  Theory and Application of the
PORFLOW Model for Analysis of Coupled Flow, Heat and
Radionuclide Transport in Porous Media. Proceedings,
international Symposium on Coupled Processes Affecting the
Performance of a Nuclear Waste Repository, Berkeley,
California.

Salhotra, A.M., P. Mineart, S. Sharp-Hansen, and T. Allison,
(1990).  Multimedia Exposure Assessment Model (MULTIMED) for
Evaluating the Land Disposal of Wastes--Model Theory. 
Prepared for U.S. Environmental Protection Agency,
Environmental Research Laboratory, Athens, Georgia.

Schroeder, A.C., A.C. Gibson, and M.D. Smolen, (1984).  The
Hydrologic Evaluation of Landfill Performance (HELP) Model,
Volumes I and II.  EPA/530/SW-009 and EPA/530/SW-010, U.S.
Environmental Protection Agency,  Cincinnati, Ohio.

Sharp-Hansen, S., C. Travers, P. Hummel, and T. Allison,
(1990).  A Subtitle D Landfill Application Manual for the
Multimedia Exposure Assessment Model (MULTIMED).  Prepared
for the U.S. EPA, Environmental Research Laboratory, Athens,
Georgia.

Summers, K.V., S.A. Gherini, M.M. Lang, M.J. Ungs, and K.J.
Wilkinson, (1989). MYGRT Code Version 2.0: An IBM Code for
Simulating Migration of Organic and Inorganic Chemicals in
Groundwater.  EN-6531.  Electric Power Research Institute,
Palo Alto, California.

Temple, Barker and Sloane, Inc., (1988).  Draft Regulatory
Impact Analysis of Proposed Revisions to Subtitle D Criteria
for Municipal Solid Waste Landfills.  Prepared for Office of
Solid Waste, U.S. Environmental Protection Agency.
Note:  Office of Solid Waste, OSW, was renamed Office of Resource Conservation and Recovery, ORCR, on January 18, 2009

Theis, T.L., D.J. Kirkner and A.A. Jennings, (1982). 
Multi-Solute Subsurface Transport Modeling for Energy Solid
Wastes.  Technical Progress Report for the Period September
1, 1981-August 31, 1982, COO-10253-3, Prepared for
Ecological Research Division, Office of Health and
Environmental Research, U.S. Department of Energy.

Travers, C.L., and S. Sharp-Hansen, (1991).  Leachate
Generation and Migration at Subtitle D Facilities: A Summary
and Review of Processes and Mathematical Models.  Prepared
for U.S. EPA, Environmental Research Laboratory, Athens,
Georgia.

Travis, B., (1984).  TRACR3D: A Model of Flow and Transport
in Porous/Fractured Media.  LA-9667-MS.  Los Alamos National
Laboratory, Los Alamos, New Mexico.

Unge, M.J., K.V. Summers, and S.A. Gherini, (1986).  MYGRT:
An IBM Personal Computer Code for Simulation Solute
Migration in Groundwater, User's Manual.  EA-4545-CCM. 
Electric Power Research Institute, Palo Alto, California.

U.S. EPA, (1988).  Superfund Exposure Assessment Manual. 
EPA/540/1-88/001, Washington, DC.  NTIS No. PB89-135859. 
157 pp.

U.S. EPA, (1993).  Compilation of Ground-Water Models;
PB93-209401; U.S. EPA; Office of Solid Waste; Washington,
D.C.
Note:  Office of Solid Waste, OSW, was renamed Office of Resource Conservation and Recovery, ORCR, on January 18, 2009

van der Heijde, P.K., Y. Bachmat, J. Bredehoeft, B. Andrews,
D. Holtz, and S. Sebastian, (1985).  Groundwater Management: 
The Use of Numerical Models.  American Geophysical Union,
Washington, D.C.

van der Heijde, P.K., and M.S. Beljin, (1988a).  Model
Assessment for Delineating Wellhead Protection Areas. 
EPA-440/6-88-002, U.S. EPA, Washington, DC.  

van der Heijde, P.K., El-Kadi, A.I., and S.A. Williams,
(1988b).  Groundwater Modeling: An Overview and Status
Report.  EPA/600/2-89/028, U.S. EPA, Ada, Oklahoma.  

van Genuchten, M.T., (1978).  Simulation Models and Their
Application to Landfill Disposal Siting; A Review of Current
Technology.  In Land Disposal of Hazardous Wastes. 
EPA-660/9-78-016, U.S. EPA, Cincinnati, Ohio. 

van Genuchten, M.T., and W.J. Alves, (1982).  Analytical
Solutions of the One-Dimensional Convective-Dispersive
Solute Transport Equation.  USDA, Technique Bulletin No.
1661.  U.S. Department of Agriculture, Washington, DC.

Versar, Inc., (1987).  Current and Suggested Practices in
the Validation of Exposure Assessment Models, Draft Report. 
Prepared for U.S. EPA Office of Health and Environmental
Assessment, Exposure Assessment Group, Washington, DC.  EPA
Contract No. 69-02-4254, Work Assignment No. 55.  

Voss, C.I., (1984).  SUTRA: A Finite Element Simulation
Model for Saturated-Unsaturated Fluid Density-Dependent
Groundwater Flow with Energy Transport or Chemically
Reactive Single Species Solute Transport.  Water Resources
Investigations 84-4369, U.S. Geological Survey.

Walton, W.C., (1984).  35 Basic Groundwater Model Programs
for Desktop Microcomputers.  GWMI 84-06/4, International
Groundwater Modeling Center, Holcomb Research Institute,
Butler University, Indianapolis, Indiana.

Weaver, J., C.G. Enfield, S. Yates, D. Kreamer, and D.
White, (1989).  Predicting Subsurface Contaminant Transport
and Transformation:  Considerations for Model Selection and
Field Validation.  U.S. EPA, Ada, Oklahoma.

Yeh, G.T., (1981).  AT123D:  Analytical, Transient, One-,
Two-, Three-Dimensional Simulation of Waste Transport in the
Aquifer System.  Publication No. 1439. Oak Ridge National
Laboratory, Oak Ridge, Tennessee.

Yeh, G.T., (1990).  Users' Manual of a Three-Dimensional
Hybrid Lagrangian-Eulerian Finite Element Model of WASTE
Transport through Saturated-Unsaturated Media.  Pennsylvania
State University, University Park, PA.

Yeh, G.T., and D.S. Ward, (1981).  FEMWASTE:  A
Finite-Element Model of Waste Transport through
Saturated-Unsaturated Porous Media.  ORNL-5601.  Oak Ridge
National Laboratory, Oak Ridge, Tennessee.

Yeh, G.T., and D.S. Ward, (1987).  FEMWATER:  A
Finite-Element Model of Water Flow through
Saturated-Unsaturated Porous Media.  ORNL-5567/R1.  Oak
Ridge National Laboratory, Oak Ridge, Tennessee.


     4.6.2  References (Specific to Design Criteria)

ASCE, (1969).  "Design and Construction of Sanitary and
Storm Sewers"; ASCE Manual on Engineering Practice; No. 37.

Bear, Jacob and Arnold Veruijt, (1987).  "Modeling
Groundwater Flow and Pollution"; D. Reidel Publishing
Company; Dordracht, Holland.

Benson, Craig H. and David E. Daniel, (1990).  "Influence of
Clods on Hydraulic Conductivity of Compacted Clay"; Journal
of Geotechnical Engineering; Volume 116, No. 8; August,
1990.

Bonaparte, R. and Gross, B.A., (1990).  "Field Behavior of
Double-Liner Systems.  In Waste Containment Systems: 
Construction, Regulation, and Performance, Edited by R.
Bonaparte.  Geotechnical Pub 1.26, ASCE.

Carroll, Jr., R.G., (1987).  "Hydraulic Properties of
Geotextiles."  Geotextile Testing and the Design Engineers,
ASTEM 952, American Society for Testing and Materials,
Philadelphia, PA, pp 7-20.

COE, (1970).  "Laboratory Soils Testing"; EM1110-2-1906;
Headquarters, Department of the Army; Office of the Chief of
Engineers; Washington, DC  20314.

FHWA, (1985).  "FHWA Geotextile Engineering Manual." 
Contract No.l DTF H61-83-C-00150.

FHWA, (1990).  "Geotextile Design & Construction Guidelines. 
Contract No. FHWA DTFH61-86-C-00102. 

GCA Corporation, (1983).  "Draft Permit Writers' Guidance
Manual for Hazardous Waste Treatment, Storage, and Disposal
Facility"; 1983.

Giroud, J.P., (1982).  "Filter Criteria for Geotextiles,"
Proceeding 2nd International Conference on Geotextiles, Las
Vegas, Nevada.

Giroud, J.P. and R. Bonaparte, (1989).  "Leakage Through
Liners Constructed with Geomembranes - Part I:  Geomembrane
Liners"; Geotextiles and Geomembranes 8(2); 0266-1144/89;
pp. 27-67; Elsevier Science Publishers Ltd., England, Great
Britain.

Giroud, J.P. and R. Bonaparte, (1989).  "Leakage Through
Liners Constructed with Geomembranes - Part II:  Composite
Liners"; Geotextiles and Geomembranes 8(2); 0266-1144/89;
pp. 71-111; Elsevier Science Publishers Ltd., England, Great
Britain.

Giroud, J.P., A. Khatami and K. Badu-Tweneboah, (1989). 
"Technical Note - Evaluation of the Rate of Leakage Through
Composite Liners"; Geotextiles and Geomembranes 8;
0266-1144/89; pp. 337-340; Elsevier Science Publishers Ltd.,
England, Great Britain.

Haxo, H.E., Jr., (1983).  "Analysis and Fingerprinting of
Unexposed and Exposed Polymeric Membrane Liners";
Proceedings of Ninth Annual Research Symposium:  Land
Disposal, Incineration, and Treatment of Hazardous Waste;
EPA/600/9-83/018; U.S. EPA; Cincinnati, Ohio.

Haxo, H.E., Jr., J.A. Miedema and H.A. Nelson, (1984). 
"Permeability of Polymeric Membrane Lining Materials";
Matrecon, Inc.; Oakland, California; International
Conference on Geomembranes; Denver, Colorado.

Industrial Fabrics Association International (1990).  "1991
Specifiers Guide;" Geotechnical Fabrics Report, Volume 8,
No. 7, 1990.

Javendale, I., C. Doughty and C.F. Tsang, (1984). 
"Groundwater Transport; Handbook of Mathematical Models";
American Geophysical Union; Washington, DC  20009.

Jayawickrama, P.W., K.W. Brown, J.C. Thomas and R.L. Lytton,
(1988).  "Leakage Rates Through Flaws in Membrane Liners";
Journal of Environmental Engineering; Vol. 114, No. 6;
December, 1988.

Kastman, Kenneth A., (1984).  "Hazardous Waste Landfill
Geomembrane:  Design, Installation and Monitoring";
Woodward-Clyde Consultants, Chicago, Illinois; International
Conference on Geomembranes; Denver, Colorado.

Koerner, Robert M., (1990).  "Designing with Geosynthetics";
2nd Edition; Prentice Hall; Englewood-Cliffs, New Jersey 
07632.


Radian Corporation, (1987).  "Technical Data Summary: 
Hydraulic Performance of Minimum Technology Double Liner
Systems"; Radian Corporation; Austin, Texas 78766 for U.S.
EPA; Contract No. 68-01-7310; Task 7-4.

U.S. EPA, (1982).  "Landfill and Surface Impoundment
Performance Evaluation"; SW-869; Charles A. Moore; U.S. EPA. 
NTIS PB-81-166357.

U.S. EPA, (1983).  "Lining of Waste Impoundment and Disposal
Facilities"; SW-870; U.S. EPA; Office of Solid Waste and
Emergency Response; Washington, DC 20460.  NTIS PB-81-166365
Revised: PB-86-192796.


U.S. EPA, (1987a).  "Background Document on Bottom Liner
Performance in Double-Lined Landfills and Surface
Impoundments"; EPA/530/SW-87/013; U.S. EPA; Washington, DC. 
NTIS PB-87-182291.

U.S. EPA, (1987b)  " Characterization of MWC Ashes and
Leachates from MSW Landfills, Monofills and Co-Disposal
Sites: Volume VI of VII ; Characterization of Leachates from
Municipal Solid Waste Disposal Sites and Co-Disposal Sites";
EPA/530/SW-87/028F, Washington, D.C.  NTIS PB-88-127998.

U.S. EPA, (1988).  "Guide to Technical Resources for the
Design of Land Disposal Facilities"; EPA/625/6-88/018; U.S.
EPA; Risk Reduction Engineering Laboratory; Center for
Environmental Research Information; Cincinnati, Ohio  45268.

U.S. EPA, (1988a).  Superfund Exposure Assessment Manual. 
EPA/540/1-88/001, Washington, D.C., NTIS No. PB89-135.859,
157 pp.

U.S. EPA, (1988b).  "Design, Construction and Evaluation of
Clay Liners for Waste Management Facilities;
EPA/530/SW-86/007F; U.S. EPA; Office of Solid Waste and
Emergency Response; Washington, DC  20460.  NTIS
PB-86-184496.

U.S. EPA, (1988c).  "Groundwater Modeling:  An Overview and
Status Report";     EPA/600/2-89/028; U.S. EPA;
Environmental Research Laboratory; Ada, Oklahoma  74820. 
NTIS PB-89-224497.

U.S. EPA, (1988d).  "Multimedia Exposure Assessment Model
for Evaluating the Land Disposal of Hazardous Wastes, Volume
I.";  Woodward-Clyde Consultants, Oakland, CA  94607-4014
for U.S. EPA; Environmental Research Laboratory; Office of
Research and Development; Athens, Georgia  30613.

U.S. EPA, (1988e).  "Lining of Waste Containment and Other
Impoundment Facilities"; EPA/600/2-88/052; U.S. EPA; Risk
Reduction Engineering Laboratories; Cincinnati, Ohio  45268. 
NTIS PB-89-129670.

U.S. EPA, (1989).  "Seminar Publication - Requirements for
Hazardous Waste Landfill Design, Construction and Closure";
EPA/625/4-89/022; U.S. EPA; Center for Environmental
Research Information; Office of Research and Development;
Cincinnati, Ohio  45268.

U.S. EPA, (1990a).  "Seminars - Design and Construction of
RCRA/CERCLA Final Covers", CERI 90-50; U.S. EPA; Office of
Research and Development; Washington, DC  20460.

U.S. EPA, (1990b).  "Draft - LDCRS Flow Data from Operating
Units - Technical Support for Proposed Liner/Leak Detection
System Rule"; Geoservices, Inc. Consulting Engineers;
Norcross, Georgia  30093.

U.S. EPA, (1990c).  "Relationship of Laboratory- and
Field-Determined Hydraulic Conductivity in Compacted Clay
Layer"; EPA/600/2-90/025; U.S. EPA; Risk Reduction
Engineering Laboratory; Cincinnati, Ohio  45268.  NTIS
PB-90-257775.

U.S. EPA, (1991a).  "Technical Guidance Document: Inspection
Techniques for the Fabrication of Geomembrane Field Seams";
EPA 530/SW-91/051, May 1991, Cincinnati, Ohio.

U.S. EPA, (1991b).  "Landfill Leachate Clogging of
Geotextiles (and Soil) Filters"; EPA/600/2-91/025, August
1991; Risk Reduction Engineering Laboratory; Cincinnati,
Ohio, 45268.  NTIS PB-91-213660.

U.S. EPA, (1992).  "Technical Guidance Document: 
Construction Quality Management for
Remedial Action and Remedial Design Waste Containment
Systems"; EPA/540/R-92/073, October 1992; Risk Reduction
Engineering Laboratory, Cincinnati, Ohio 45268 and
Technology Innovation Office, Washington, D.C. 20460.


     4.6.3  Models

List of Contacts for Obtaining Leachate Generation and
Leachate Migration Models

Center for Exposure Assessment Modeling (CEAM), U.S. EPA,
Office of Research and Development, Environmental Research
Laboratory, Athens, Georgia  30605-2720, Model Distribution
Coordinator (706) 546-3549, Electronic Bulletin Board System
(706) 546-3402: MULTIMED, PRZM, FEMWATER/FEMWASTE,
LEWASTE/3DLEWASTE

Electric Power Research Institute, Palo Alto, California,
(214) 655-8883: MYGRT, FASTCHEM

Geo-Trans Inc., 46050 Manekin Plaza, Suite 100, Sterling, VA
20166, (703) 444-7000: SWANFLOW, SWIFT, SWIFT II, SWIFT III,
SWIFT/386.

Geraghty & Miller, Inc., Modeling Group, 10700 Parkridge
Boulevard, Suite 600 Reston, VA 22091: MODFLOW386,
MODPATH386, MOC386, SUTRA386, Quickflow, 

International Groundwater Modeling Center, Colorado School
of Mines, Golden, Colorado
(303) 273-3103: SOLUTE, Walton35, SEFTRAN, TRAFRAP,

National Technical Information Services (NTIS), 5285 Port
Royal Road, Springfield, VA 22161, (703) 487-4650: HELP

Dr. Zubair Saleem, U.S. EPA, 401 M Street SW, Washington,
DC, 20460, (202) 260-4767:
EPACML, VHS

Scientific Software Group, P.O. Box 23041, Washington, DC
20026-3041 (703) 620-9214: HST3D, MODFLOW, MOC, SUTRA, AQUA,
SWIMEV.