Part IV

Protecting Ground Water

Chapter 7: Section B

Designing and Installing Liners

Technical Considerations for New Surface

Impoundments, Landfills, and Waste Piles
Contents

I. In-Situ Soil Liners ..................................................................................................................................7B-1

II. Single Liners ..........................................................................................................................................7B-2

A. Compacted Clay Liners ........................................................................................................................7B-2

B. Geomembranes or Flexible Membrane Liners ....................................................................................7B-10

C. Geosynthetic Clay Liners ....................................................................................................................7B-17

III. Composite Liners..................................................................................................................................7B-22

IV. Double Liners (Primary and Secondary Lined Systems) ........................................................................7B-23

V. Leachate Collection and Leak Detection Systems ..................................................................................7B-24

A. Leachate Collection System..................................................................................................................7B-24

B. Leak Detection System ........................................................................................................................7B-28

C. Leachate Treatment System ..................................................................................................................7B-29

VI. Construction Quality Assurance and Quality Control ..........................................................................7B-29

A. Compacted Clay Liner Quality Assurance and Quality Control ..........................................................7B-32

B. Geomembrane Liner Quality Assurance and Quality Control ..............................................................7B-32

C. Geosynthetic Clay Liner Quality Assurance and Quality Control ........................................................7B-33

D. Leachate Collection System Quality Assurance and Quality Control....................................................7B-34

Designing and Installing Liners Activity List................................................................................................7B-36

Resources ....................................................................................................................................................7B-37

Appendix ....................................................................................................................................................7B-43

Figures:

Figure 1. Water Content for Achieving a Specific Density ..........................................................................7B-6

Figure 2: Two Types of Footed Rollers........................................................................................................7B-8

Figure 3: Four Variations of GCL Bonding Methods ................................................................................7B-19

Figure 4: Typical Leachate Collection System ..........................................................................................7B-25

Figure 5: Typical Geonet Configuration....................................................................................................7B-27
Protecting Ground Water—Designing and Installing Liners

7B-1

Once risk has been characterized

and the most appropriate

design system is chosen, the

next step is unit design. The

Industrial Waste Management

Evaluation Model (IWEM), discussed in

Chapter 7, Section A—Assessing Risk can be

used to determine appropriate design system

recommendations. A critical part of this

design for new landfills, waste piles, and surface impoundments is the liner system. The

liner system recommendations in the Guide

do not apply to land application units, since

such operations generally do not include a

liner system as part of their design. (For

design of land application units, refer to

Chapter 7, Section C—Designing a Land

Application Program.) You should work with

your state agency to ensure consideration of

any applicable design system requirements,

recommendations, or standard practices the

state might have. In this chapter, sections I

though IV discuss four design options—no

liner/in-situ soils, single liner, composite liner,

and double liner. Section V covers leachate

collection and leak detection systems, and

section VI discusses construction quality

assurance and quality control.

I. In-Situ Soil

Liners

For the purpose of the Guide, in-situ soil

refers to simple, excavated areas or impoundments, without any additional engineering

controls. The ability of natural soils to hinder

transport and reduce the concentration of

constituent levels through dilution and attenuation can provide sufficient protection when

the initial constituent levels in the waste

stream are very low, when the wastes are

inert, or when the hydrogeologic setting

affords sufficient protection.

What are the recommendations

for in-situ soils?

The soil below and adjacent to a waste

management unit should be suitable for construction. It should provide a firm foundation

for the waste. Due to the low risk associated

with wastes being managed in these units, a

liner might not be necessary; however, it is

still helpful to review the recommended location considerations and operating practices for

the unit.

Designing and Installing Liners—Technical

Considerations for New Surface

Impoundments, Landfills, and Waste Piles

This chapter will help you:

• Employ liner systems where needed to protect ground water from

contamination. 

• Select from clay liners, synthetic liners, composite liners, leachate

collection systems, and leak detection systems as appropriate. 

• Consider technical issues carefully to ensure that the liner system

will function as designed.
7B-2

Protecting Ground Water—Designing and Installing Liners 

1 Many industry and trade periodicals, such as Waste Age, MSW Management, Solid Waste Technologies,

and World Wastes, have articles on liner types and their corresponding costs, as well as advertisements

and lists of vendors.

What technical issues should be

considered with the use of in-situ

soils?

In units using in-situ natural soils, construction and design of an engineered liner

will not be necessary; however, there are still

technical concerns to consider. These include

the following:

• The stability of foundation soils.

• The compatibility of the waste with

native soils.

• The location where the unit will be

sited.

• The potential to recompact existing

soils.

Potential instability can occur in the foundation soil, if its load-bearing capacity and

resistance to movement or consolidation are

insufficient to support the waste. The groundwater table or a weak soil layer also can influence the stability of the unit. You should take

measures, such as designing maximum slopes,

to avoid slope failure during construction and

operation of the waste management unit. Most

soil slopes are stable at a 3:1 horizontal to vertical inclination. There are common sense

operating practices to ensure that any wastes

to be managed on in-situ soils will not inappropriately interact with the soils. When using

in-situ soils, refer to Chapter 4—Considering

the Site. Selecting an appropriate location will

be of increased importance, since the added

barrier of an engineered liner will not be present. Because in-situ soil can have non-homogeneous material, root holes, and cracks, its

performance can be improved by scarifying

and compacting the top portion of the in-situ

natural soils.

II. Single Liners

If the risk evaluation recommended the use

of a single liner, the next step is to determine

the type of single liner system most appropriate for the site. The discussion below addresses three types of single liner systems:

compacted clay liners, geomembrane liners,

and geosynthetic clay liners. Determining

which material, or combination of materials, is

important for protecting human health and

the environment.1

A. Compacted Clay Liners 

A compacted clay liner can serve as a single

liner or as part of a composite or double liner

system. Compacted clay liners are composed

of natural mineral materials (natural soils),

bentonite-soil blends, and other materials

placed and compacted in layers called lifts. If

natural soils at the site contain a significant

quantity of clay, then liner materials can be

excavated from onsite locations known as borrow pits. Alternatively, if onsite soils do not

contain sufficient clay, clay materials can be

hauled from offsite sources, often referred to

as commercial pits.

Compacted clay liners can be designed to

work effectively as hydraulic barriers. To

ensure that compacted clay liners are well

constructed and perform as they are designed,

it is important to implement effective quality

control methods emphasizing soil investigations and construction practices. Three objectives of quality assurance and quality control

for compacted soil liners are to ensure that 1)

selected liner materials are suitable, 2) liner

materials are properly placed and compacted,

and 3) the completed liner is properly protected before, during, and after construction.

Quality assurance and quality control are discussed in greater detail in section VI.
What are the thickness and

hydraulic conductivity recommendations for compacted clay liners?

Compacted clay liners should be at least 2

feet thick and have a maximum hydraulic

conductivity of 1 x 10-7 cm/sec (4 x 10-8

in/sec). Hydraulic conductivity refers to the

degree of ease with which a fluid can flow

through a material. A low hydraulic conductivity will help minimize leachate migration

out of a unit. Designing a compacted clay

liner with a thickness ranging from 2 to 5 feet

will help ensure that the liner meets desired

hydraulic conductivity standards and will

also minimize leachate migration as a result

of any cracks or imperfections present in the

liner. Thicker compacted clay liners provide

additional time to minimize leachate migration prior to the clay becoming saturated.

What issues should be considered

in the design of a compacted clay

liner?

The first step in designing a compacted

clay liner is selecting the clay material. The

quality and properties of the material will

influence the performance of the liner. The

most common type of compacted soil is one

that is constructed from naturally occurring

soils that contain a significant quantity of

clay. Such soils are usually classified as CL,

CH, or SC in the Unified Soil Classification

System (USCS). Some of the factors to consider in choosing a soil include soil properties, interaction with wastes, and test results

for potentially available materials.

Soil Properties

Minimizing hydraulic conductivity is the

primary goal in constructing a soil liner.

Factors to consider are water content, plasticity

characteristics, percent fines, and percent gravel, as these properties affect the soil’s ability to

achieve a specified hydraulic conductivity.

Hydraulic conductivity. It is important to

select compacted clay liner materials so that

remolding and compacting of the materials

will produce a low hydraulic conductivity.

Factors influencing the hydraulic conductivity at a particular site include: the degree of

compaction, compaction method, type of clay

material used, soil moisture content, and

density of the soil during liner construction.

The hydraulic conductivity of a soil also

depends on the viscosity and density of the

fluid flowing through it. Consider measuring

hydraulic conductivity using methods such as

American Society of Testing and Materials

(ASTM) D-5084.2

Water content. Water content refers to the

amount of liquid, or free water, contained in a

given amount of material. Measuring water

content can help determine whether a clay

material needs preprocessing, such as moisture

adjustment or soil amendments, to yield a

specified density or hydraulic conductivity.

Compaction curves can be used to depict

moisture and density relationships, using

either ASTM D-698 or ASTM D-1557, the

standard or modified Proctor test methods,

depending on the compaction equipment used

and the degree of firmness in the foundation

materials.3 The critical relationship between

clay soil moisture content and density is

explained thoroughly in Chapter 2 of EPA’s

1993 technical guidance document Quality

Protecting Ground Water—Designing and Installing Liners

7B-3

2 ASTM D-5084, Standard Test Method for Measurement of Hydraulic Conductivity of Saturated Porous

Materials Using a Flexible Wall Permeameter.

3 ASTM D-698, Test Method for Laboratory Compaction Characteristics of Soil Using Standard Effort

(12,400 ft-lbf/ft3 (600 kN-m/m3)).

ASTM D-1557, Test Method for Laboratory Compaction Characteristics of Soil Using Modified Effort

(56,000 ft-lbf/ft3 (2,700 kN-m/m3

)).
7B-4

Protecting Ground Water—Designing and Installing Liners 

Assurance and Quality Control for Waste

Containment Facilities (U.S. EPA, 1993c).

Plasticity characteristics. Plasticity characteristics describe a material’s ability to

behave as a plastic or moldable material.

Soils containing clay are generally categorized

as plastic. Soils that do not contain clay are

non-plastic and typically considered unsuitable materials for compacted clay liners,

unless soil amendments such as bentonite

clay are introduced. 

Plasticity characteristics are quantified by

three parameters: liquid limit, plastic limit,

and plasticity index. The liquid limit is

defined as the minimum moisture content (in

percent of oven-dried weight) at which a soilwater mixture can flow. The plastic limit is

the minimum moisture content at which a

soil can be molded. The plasticity index is

defined as the liquid limit minus the plastic

limit and defines the range of moisture content over which a soil exhibits plastic behavior. When soils with high plastic limits are

too dry during placement, they tend to form

clods, or hardened clumps, that are difficult

to break down during compaction. As a

result, preferential pathways can form around

these clumps allowing leachate to flow

through the material at a higher rate. Soil

plasticity indices typically range from 10 percent to 30 percent. Soils with a plasticity

index greater than 30 percent are cohesive,

sticky, and difficult to work with in the field.

Common testing methods for plasticity characteristics include the methods specified in

ASTM D-4318, also known as Atterberg limits tests.4

Percent fines and percent gravel. Typical

soil liner materials contain at least 30 percent

fines and can contain up to 50 percent gravel,

by weight. Common testing methods for percent fines and percent gravel are specified in

ASTM D-422, also referred to as grain size

distribution tests.5 Fines refer to silt and claysized particles. Soils with less than 30 percent

fines can be worked to obtain hydraulic conductivities below 1 x 10-7 cm/sec (4 x 10-8

in./sec), but use of these soils requires more

careful construction practices.

Gravel is defined as particles unable to

pass through the openings of a Number 4

sieve, which has an opening size equal to

4.76 mm (0.2 in.). Although gravel itself has

a high hydraulic conductivity, relatively large

amounts of gravel, up to 50 percent by

weight, can be uniformly mixed with clay

materials without significantly increasing the

hydraulic conductivity of the material. Clay

materials fill voids created between gravel

particles, thereby creating a gravel-clay mixture with a low hydraulic conductivity. As

long as the percent gravel in a compacted

clay mixture remains below 50 percent, creating a uniform mixture of clay and gravel,

where clay can fill in gaps, is more critical

than the actual gravel content of the mixture. 

You should pay close attention to the percent gravel in cases where a compacted clay

liner functions as a bottom layer to a geosynthetic, as gravel can cause puncturing in

geosynthetic materials. Controlling the maximum particle size and angularity of the gravel should help prevent puncturing, as well as

prevent gravel from creating preferential flow

paths. Similar to gravel, soil particles or rock

fragments also can create preferential flow

paths. To help prevent the development of

preferential pathways and an increased

hydraulic conductivity, it is best to use soil

liner materials where the soil particles and

rock fragments are typically small (e.g., 3/4

inch in diameter).

Interactions With Waste

Waste placed in a unit can interact with

compacted clay liner materials, thereby influencing soil properties such as hydraulic con4 ASTM D-4318, Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of Soils.

5 ASTM D-422, Standard Test Method for Particle-Size Analysis of Soils.
Protecting Ground Water—Designing and Installing Liners

7B-5

6 SW-846, Test Methods for Evaluating Solid Waste: Physical/Chemical Methods.

ductivity and permeability. Two ways that

waste materials can influence the hydraulic

conductivity of the liner materials are

through dissolution of soil minerals and

changes in clay structure. Soil minerals can

be dissolved, or reduced to liquid form, as a

result of interaction with acids and bases. For

example, aluminum and iron in the soil can

be dissolved by acids, and silica can be dissolved by bases. While some plugging of soil

pores by dissolved minerals can lower

hydraulic conductivity in the short term, the

creation of piping and channels over time can

lead to an increased hydraulic conductivity in

the long term. The interaction of waste and

clay materials can also cause the creation of

positive ions, or cations. The presence of

cations such as sodium, potassium, calcium,

and magnesium can change the clay structure, thereby influencing the hydraulic conductivity of the liner. Depending on the

cation type and the clay mineral, an increased

presence of such cations can cause the clay

minerals to form clusters and increase the

permeability of the clay. Therefore, before

selecting a compacted clay liner material, it is

important to develop a good understanding

of the composition of the waste that will be

placed in the waste management unit. EPA’s

Method 9100, in publication SW-846, measures the hydraulic conductivity of soil samples before and after exposure to permeants.6

Locating and Testing Material

Although the selection process for compacted clay liner construction materials can

vary from project to project, some common

material selection steps include locating and

testing materials at a potential borrow or

commercial pit before construction, and

observing and testing material performance

throughout construction. First, investigate a

potential borrow or commercial pit to determine the volume of materials available. The

next step is to test a representative sample of

soil to determine material properties such as

plasticity characteristics, percent gravel, and

percent fines. To confirm the suitability of the

materials once construction begins, you

should consider requesting that representative samples from the materials in the borrow

or commercial pit be tested periodically after

work has started. 

Material selection steps will vary, depending on the origin of the materials for the project. For example, if a commercial pit provides

the materials, locating an appropriate onsite

borrow pit is not necessary. In addition to the

tests performed on the material, it is recommended that a qualified inspector make visual

observations throughout the construction

process to ensure that harmful materials, such

as stones or other large matter, are not present

in the liner material.

What issues should be considered

in the construction of a liner and

the operation of a unit?

You should develop test pads to demonstrate construction techniques and material

performance on a small scale. During unit construction and operation, some additional factors influencing the performance of the liner

include: preprocessing, subgrade preparation,

method of compaction, and protection against

desiccation and cracking. Each of these steps,

from preprocessing through protection against

desiccation and cracking, should be repeated

for each lift or layer of soil.

Test Pads

Preparing a test pad for the compacted

clay liner helps verify that the materials and

methods proposed will yield a liner that

meets the desired hydraulic conductivity. A

test pad also provides an opportunity to
7B-6

Protecting Ground Water—Designing and Installing Liners 

demonstrate the performance of alternative

materials or methods of construction. A test

pad should be constructed with the soil liner

materials proposed for a particular project,

using the same preprocessing procedures,

compaction equipment, and construction

practices proposed for the actual liner. A

complete discussion of test pads (covering

dimensions, materials, and construction) can

be found in Chapter 2 of EPA’s 1993 technical guidance document Quality Assurance and

Quality Control for Waste Containment Facilities

(U.S. EPA, 1993c). A discussion of commonly

used methods to measure in-situ hydraulic

conductivity is also contained in that chapter.

Preprocessing

Although some liner

materials can be ready

for use in construction

immediately after they

are excavated, many

materials will require

some degree of preprocessing. Preprocessing

methods include: water

content adjustment,

removal of oversized

particles, pulverization

of any clumps, homogenization of the soils, and

introduction of additives, such as bentonite.

Water content

adjustment. For natural

soils, the degree of saturation of the soil liner at

the time of compaction,

known as molding water

content, influences the

engineering properties of

the compacted material.

Soils compacted at water

contents less than optimum tend to have a relatively high hydraulic

conductivity. Soils compacted at water contents greater than optimum tend to have low

hydraulic conductivity and low strength. 

Proper soil water content revolves around

achieving a minimum dry density, which is

expressed as a percentage of the soil’s maximum dry density. The minimum dry density

typically falls in the range of 90 to 95 percent

of the soil’s maximum dry density value. From

the minimum dry density range, the required

water content range can be calculated, as

shown in Figure 1. In this example the soil

has a maximum dry density of 115 lb/cu ft.

Based upon a required minimum dry density

value of 90 percent of maximum dry density,

Figure 1. 

Water Content for Achieving a Specific Density

Source: U.S. EPA, 1988.
Protecting Ground Water—Designing and Installing Liners

7B-7

which is equal to 103.5 lb/cu ft, the required

water content ranges from 10 to 28 percent.

It is less problematic to compact clay soil

at the lower end of the required water content range because it is easier to add water to

the clay soil than to remove it. Thus, if precipitation occurs during construction of a site

which is being placed at the lower end of the

required water content range, the additional

water might not result in a soil water content

greater than the required range. Conversely, if

the site is being placed at the upper end of

the range, for example at 25 percent, any

additional moisture will be excessive, resulting in water content over 28 percent and

making the 90 percent maximum dry density

unattainable. Under such conditions construction should halt while the soil is aerated

and excess moisture is allowed to evaporate.

Removal of oversized particles.

Preprocessing clay materials, to remove cobbles or large stones that exceed the maximum

allowable particle size, can improve the soil’s

compactibility and protect any adjacent

geomembrane from puncture. Particle size

should be small (e.g., 3/4 inch in diameter)

for compaction purposes. If a geomembrane

will be placed over the compacted clay, only

the upper lift of clay needs to address concerns regarding puncture resistance.

Observation by quality assurance and quality

control personnel is the most effective

method to identify areas where oversized particles need to be removed. Cobbles and

stones are not the only materials that can

interfere with compactive efforts. Chunks of

dry, hard clay, also known as clods, often

need to be broken into smaller pieces to be

properly hydrated, remolded, and compacted. In wet clay, clods are less of a concern

since wet clods can often be remolded with a

reasonable compactive effort.

Soil amendments. If the soils at a unit do

not have a sufficient percentage of clay, a common practice is to blend bentonite with them

to reduce the hydraulic conductivity. Bentonite

is a clay mineral that expands when it comes

into contact with water. Relatively small

amounts of bentonite, on the order of 5 to 10

percent, can be added to sand or other noncohesive soils to increase the cohesion of the

material and reduce hydraulic conductivity. 

Sodium bentonite is a common additive

used to amend soils. However, this additive is

vulnerable to degradation as a result of contact with certain chemicals and waste

leachates. Calcium bentonite, a more permeable material than sodium bentonite, is another common additive used to amend soils.

Approximately twice as much calcium bentonite is needed to achieve a hydraulic conductivity comparable to that of sodium

bentonite. Amended soil mixtures generally

require mixing in a pug mill, cement mixer, or

other mixing equipment that allows water to

be added during the mixing process.

Throughout the mixing and placement

processes, water content, bentonite content,

and particle distribution should be controlled.

Other materials that can be used as soil additives include lime cement and other clay minerals, such as atapulgite. It can be difficult to

mix additives thoroughly with cohesive soils,

or clays; the resultant mixture might not

achieve the desired level of hydraulic conductivity throughout the entire liner. 

Subgrade Preparation

It is important to ensure that the subgrade

on which a compacted clay liner will be constructed is properly prepared. When a compacted clay liner is the lowest component of a

liner system, the subgrade consists of native

soil or rock. Subgrade preparation for these

systems involves compacting the native soil

to remove any soft spots and adding water to

or removing water from the native soil to

obtain a specified firmness. Alternatively, in
7B-8

Protecting Ground Water—Designing and Installing Liners 

some cases, the compacted clay liner can be

placed on top of a geosynthetic material, such

as a geotextile. In such cases, subgrade preparation involves ensuring the smoothness of

the geosynthetic on which the clay liner will

be placed and the conformity of the geosynthetic material to the underlying material.

Compaction

The main purpose of compaction is to

densify the clay materials by breaking and

remolding clods of material into a uniform

mass. Since amended soils usually do not

develop clumps, the primary objective of

compaction for such materials is to increase

the material’s density. Proper compaction of

liner materials is essential to ensure that a

compacted clay liner meets specified

hydraulic conductivity standards. Factors

influencing the effectiveness of compaction

efforts include: the type of equipment selected, the number of passes made over the

materials by such equipment, the lift thickness, and the bonding between the lifts.

Molding water content, described earlier

under preprocessing, is another factor influencing the effectiveness of compaction. 

Type of equipment. Factors to consider

when selecting compaction equipment

include: the type and weight of the compactor, the characteristics of any feet on the

drum, and the weight of the roller per unit

length of drummed surface. Heavy compactors, weighing more than 50,000 pounds,

with feet long enough to penetrate a loose lift

of soil, are often the best types of compactor

for clay liners. For bentonite-soil mixtures, a

footed roller might not be appropriate. For

these mixtures, where densification of the

material is more important than kneading or

remolding it to meet low hydraulic conductivity specifications, a smooth-drum roller or

a rubber- tired roller might produce better

results. Figure 2 depicts two types of footed

rollers, a fully penetrating footed roller and a

partially-penetrating footed roller.

Source: U.S. EPA, 1993c.

Figure 2 Two Types of Footed Rollers
Protecting Ground Water—Designing and Installing Liners

7B-9

For placement of liners on side slopes,

consider the angle and length of the slope.

Placing continuous lifts on a gradually

inclined slope will provide better continuity

between the bottom and sidewalls of the

liner. Since continuous lifts might be impossible to construct on steeper slopes due to the

difficulties of operating heavy compaction

equipment on these slopes, materials might

need to be placed and compacted in horizontal lifts. When sidewalls are compacted horizontally, it is important to avoid creating

seepage planes, by securely connecting the

edges of the horizontal lift with the bottom of

the liner. Because the lift needs to be wide

enough to accommodate compaction equipment, the thickness of the horizontal lift is

often greater than the thickness specified in

the design. In such cases, you should consider trimming soil material from the constructed side slopes and sealing the trimmed

surface using a sealed drum roller.

It is common for contractors to use several

different types of compaction equipment during liner construction. Initial lifts might need

the use of a footed roller to fully penetrate a

loose lift. Final lifts also might need the use

of a footed roller for compaction, however,

they might be formed better by using a

smooth roller after the lift has been compacted to smooth the surface of the lift in preparation for placement of an overlying

geomembrane.

Number of passes. The number of passes

made by a compactor over clay materials can

influence the overall hydraulic conductivity

of the liner. The minimum number of passes

that is reasonable depends on a variety of

site-specific factors and cannot be generalized. In some cases, where a minimum coverage is specified, it might be possible to

calculate the minimum number of passes to

meet such a specification. At least 5 to 15

passes with a compactor over a given point

are usually necessary to remold and compact

clay liner materials thoroughly.

An equipment pass can be defined as one

pass of the compaction equipment or as one

pass of a drum over a given area of soil. It is

important to clearly define what is meant by

a pass in any quality assurance or quality

control plans. It does not matter which definition is agreed upon, as long as the definition

is used consistently throughout the project.

Lift thickness. You should determine the

appropriate thickness (as measured before

compaction) of each of the several lifts that

will make up the clay liner. The initial thickness of a loose lift will affect the compactive

effort needed to reach the lower portions of

the lift. Thinner lifts allow compactive efforts

to reach the bottom of a lift and provide

greater assurance that compaction will be sufficient to allow homogenous bonding

between subsequent lifts. Loose lift thicknesses typically range between 13 and 25 cm (5

and 10 in.). Factors influencing lift thickness

are: soil characteristics, compaction equipment, firmness of the foundation materials,

and the anticipated compaction necessary to

meet hydraulic conductivity requirements. 

Bonding between lifts. Since it is

inevitable that some zones of higher and

lower hydraulic conductivity, also known as

preferential pathways, will be present within

each lift, lifts should be joined or bonded in a

way that minimizes extending these zones or

pathways between lifts. If good bonding is

achieved, the preferential pathways will be

truncated by the bonded zone between the

lifts. At least two recommended methods

exist for preparing proper bonds. The first

method involves kneading, or blending the

new lift with the previously compacted lift

using a footed roller. Using a roller with feet

long enough to fully penetrate through the

top lift and knead the previous lift improves

the quality of the bond. A second method
7B-10

Protecting Ground Water—Designing and Installing Liners 

involves using a disc harrow or similar equipment to scarify, or roughen, and wet the top

inch of the recently placed lift, prior to placing the next lift. 

Protection Against Desiccation and

Cracking

You should consider how to protect compacted clay liners against desiccation and

freezing during and after construction.

Protection against desiccation is important,

because clay soil shrinks as it dries. Depending on the extent of shrinkage, it can crack.

Deep cracks, extending through more than

one lift, can cause problems. You should

measure water content to determine whether

desiccation is occurring. 

There are several ways to protect compacted clay liners from desiccation. One preventive measure is to smooth roll the surface with

a steel drummed roller to produce a thin,

dense skin of soil; this layer can help minimize the movement of water into or out of the

compacted material. Another option is to wet

the clay periodically in a uniform manner;

however, it is important to make sure to avoid

creating areas of excessive wetness. A third

measure involves covering compacted clay

liner materials with a sheet of white or clear

plastic or tarp to help prevent against desiccation and cracking. The cover should be

weighted down with sandbags or other material to minimize exposure of the underlying

materials to air. Using a light-colored plastic

will help prevent overheating, which can dry

out the clay materials. If the clay liner is not

being covered with a geosynthetic, another

method to prevent desiccation involves covering the clay with a layer of protective cover

soil or intentionally overbuilding the clay liner

and shaving it down to liner grade.

Protection against freezing is another

important consideration, because freezing can

increase the hydraulic conductivity of a liner.

It is important to avoid construction during

freezing weather. If freezing does occur and

the damage affects only a shallow depth, the

liner can be repaired by rerolling the surface.

If deeper freezing occurs, the repairs might

be more complicated. For a general guide to

frost depths, see Figure 1 of Chapter 11—

Performing Closure and Post-Closure Care.

B. Geomembranes or

Flexible Membrane Liners 

Geomembranes or flexible membrane liners are used to contain or prevent waste constituents and leachate from escaping a waste

management unit. Geomembranes are made

by combining one or more plastic polymers

with ingredients such as carbon black, pigments, fillers, plasticizers, processing aids,

crosslinking chemicals, anti-degradants, and

biocides. A wide range of plastic resins are

used for geomembranes, including high density polyethylene (HDPE), linear low density

polyethylene (LLDPE), low density linear

polyethlene (LDLPE), very low density polyethlene (VLDPE), polyvinyl chloride (PVC),

flexible polypropylene (fPP), chlorosulfonated

polyethylene (CSPE or Hypalon), and ethylene propylene diene termonomer (EPDM).

Most manufacturers produce geomembranes

through extrusion or calendering. In the

extrusion process, a molten polymer is

stretched into a nonreinforced sheet; extruded geomembranes are usually made of HDPE

and LLDPE. During the calendering process,

a heated polymeric compound is passed

through a series of rollers. In this process, a

geomembrane can be reinforced with a

woven fabric or fibers. Calendered geomembranes are usually made of PVC and CSPE.
What are the thickness recommendations for geomembrane liners?

Geomembranes range in thicknesses from 20

to 120 mil (1 mil = 0.001 in.). A good design

should include a minimum thickness of 30 mil,

except for HDPE liners, which should have a

minimum thickness of 60 mil. These recommended minimum thicknesses ensure that the

liner material will withstand the stress of construction and the weight load of the waste, and

allow adequate seaming to bind separate

geomembrane panels. Reducing the potential

for tearing or puncture, through proper construction and quality control, is essential for a

geomembrane to perform effectively. 

What issues should be considered

in the design of a geomembrane

liner?

Several factors to address in the design

include: determining appropriate material

properties and testing to ensure these properties are met, understanding how the liner will

interact with the intended waste stream,

accounting for all stresses imposed by the

design, and ensuring adequate friction.

Material Properties and Selection 

When designing a geomembrane liner, you

should examine several properties of the

geomembrane material in addition to thickness, including: tensile behavior, tear resistance, puncture resistance, susceptibility to

environmental stress cracks, ultraviolet resistance, and carbon black content. 

Tensile behavior. Tensile behavior refers to

the tensile strength of a material and its ability

to elongate under strain. Tensile strength is the

ability of a material to resist pulling stresses

without tearing. The tensile properties of a

geomembrane must be sufficient to satisfy the

stresses anticipated during its service life.

These stresses include the self-weight of the

geomembrane and any down drag caused by

waste settlement on side slope liners. 

Puncture and tear resistance.

Geomembrane liners can be subject to tearing

during installation due to high winds or handling. Puncture resistance is also important to

consider since geomembranes are often

placed above or below materials that might

have jagged or angular edges. For example,

geomembranes might be installed above a

granular drainage system that includes gravel.

Susceptibility to environmental stress

cracks. Environmental factors can cause

cracks or failures before a liner is stressed to

its manufactured strength. These imperfections, referred to as environmental stress

cracks, often occur in areas where a liner has

been scratched or stressed by fatigue. These

cracks can also result in areas where excess

surface wetting agents have been applied. In

surface impoundments, where the geomembrane liner has greater exposure to the atmosphere and temperature changes, such

exposure can increase the potential for environmental stress cracking.

Ultraviolet resistance. Ultraviolet resistance is another factor to consider in the

design of geomembrane liners, especially in

cases where the liner might be exposed to

ultraviolet radiation for prolonged periods of

time. In such cases, which often occur in surface impoundments, ultraviolet radiation can

cause degradation and cracking in the

geomembrane. Adding carbon black or other

additives during the manufacturing process

can increase a geomembrane’s ultraviolet

resistance. Backfilling over the exposed

geomembrane also works to prevent degradation due to ultraviolet radiation.

Interactions With Waste

Since the main purpose of a geomembrane

is to provide a barrier and prevent contamiProtecting Ground Water—Designing and Installing Liners

7B-11
nants from penetrating through the geomembrane, chemical resistance is a critical consideration. Testing for chemical resistance might

be warranted depending on the type, volumes, and characteristics of waste managed

at a particular unit and the type of geomembrane to be used. An established method for

testing the chemical resistance of geomembranes, EPA Method 9090, can be found in

SW-846. ASTM has also adopted standards

for testing the chemical compatibility of various geosynthetics, including geomembranes,

with leachates from waste management units.

ASTM D-5747 provides a standard for testing

the chemical compatibility of

geomembranes.7

Stresses Imposed by Liner Design

A liner design should take into account the

stresses imposed on the liner by the design

configuration. These stresses include: the differential settlement in foundation soil, strain

requirements at the anchor trench, strain

requirements over long, steep side slopes,

stresses resulting from compaction, and seismic stresses. Often an anchor trench designed

to secure the geomembrane during construction is prepared along the perimeter of a unit

cell. This action can help prevent the

geomembrane from slipping down the interior side slopes. Trench designs should include

a depth of burial sufficient to hold the specified length of liner. If forces larger than the

tensile strength of the liner are inadvertently

developed, then the liner could tear. For this

reason, the geomembrane liner should be

allowed to slip or give in the trench after construction to prevent such tearing. To help

reduce unnecessary stresses in the liner design, it is advisable to avoid using horizontal

seams. For more information on design stresses, consult Geosynthetic Guidance for

Hazardous Waste Landfill Cells and Surface

Impoundments (U.S. EPA, 1987).

Designing for Adequate Friction

Adequate friction between the geomembrane liner and the soil subgrade, as well as

between any geosynthetic components, is

necessary to prevent extensive slippage or

sloughing on the slopes of a unit. Design

equations for such components should evaluate: 1) the ability of a liner to support its own

weight on side slopes, 2) the ability of a liner

to withstand down-dragging during and after

waste placement, 3) the best anchorage configuration for the liner, 4) the stability of soil

cover on top of a liner, and 5) the stability of

other geosynthetic components, such as geotextiles or geonets, on top of a liner. An evaluation of these issues can affect the choice of

geomembrane material, polymer type, fabric

reinforcement, thickness, and texture necessary to achieve the design requirements.

Interface strengths can be significantly

improved by using textured geomembranes.

What issues should be considered in the construction of a

geomembrane liner?

When preparing to construct a geomembrane liner, you should plan appropriate

shipment and handling procedures, perform

testing prior to construction, prepare the

subgrade, consider temperature effects, and

account for wind effects. In addition, you

should select a seaming process, determine a

material for and method of backfilling, and

plan for testing during construction.

Shipment, Handling, and Site Storage 

You should follow quality assurance and

quality control procedures to ensure proper

handling of geomembranes. Different types of

geomembrane liners require different types of

packaging for shipment and storage.

Typically a geomembrane manufacturer will

provide specific instructions outlining the

7B-12

7 ASTM D-5747, Practice for Tests to Evaluate the Chemical Resistance of Geomembranes to Liquids.

Protecting Ground Water—Designing and Installing Liners 
handling, storage, and construction specifications for a product. In general, HDPE and

LLDPE geomembrane liners are packaged in a

roll form, while PVC and CSPE-R liners

(CSPE-R refers to a CSPE geomembrane liner

reinforced with a fabric layer) are packaged in

panels, accordion-folded in two directions,

and placed onto pallets. Whether the liner is

shipped in rolls or panels, you should provide for proper storage. The rolls and panels

should be packaged so that fork lifts or other

equipment can safely transport them. For

rolls, this involves preparing the roll to have a

sufficient inside diameter so that a fork lift

with a long rod, known as a stinger, can be

used for lifting and moving. For accordion

panels, proper packaging involves using a

structurally-sound pallet, wrapping panels in

treated cardboard or plastic wrapping to protect against ultraviolet exposure, and using

banding straps with appropriate cushioning.

Once the liners have been transported to the

site, the rolls or panels can be stored until the

subgrade or subbase (either natural soils or

another geosynthetic) is prepared.

Subgrade Preparation 

Before a geomembrane liner is installed,

you should prepare the subgrade or subbase.

The subgrade material should meet specified

grading, moisture content, and density

requirements. In the case of a soil subgrade,

it is important to prevent construction equipment used to place the liner from deforming

the underlying materials. If the underlying

materials are geosynthetics, such as geonets

or geotextiles, you should remove all folds

and wrinkles before the liner is placed. For

further information on geomembrane placement, see Chapter 3 of EPA’s Technical

Guidance Document: Quality Assurance and

Quality Control for Waste Containment Facilities

(U.S. EPA, 1993c).

Testing Prior to Construction 

Before any construction begins, is it recommended that you test both the geomembrane

materials from the manufacturer and the

installation procedures. Acceptance and conformance testing is used to evaluate the performance of the manufactured geomembranes.

Constructing test strips can help evaluate how

well the intended construction process and

quality control procedures will work.

Acceptance and conformance testing.

You should perform acceptance and conformance testing on the geomembrane liner

received from the manufacturer to determine

whether the materials meet the specifications

requested. While the specific ASTM test

methods vary depending on geomembrane

type, recommended acceptance and conformance testing for geomembranes includes

evaluations of thickness, tensile strength and

elongation, and puncture and tear resistance

testing, as appropriate. For most geomembrane liner types, the recommended ASTM

method for testing thickness is ASTM D5199.8 For measuring the thickness of textured geomembranes, you should use ASTM

D-5994.9 For tensile strength and elongation,

ASTM D-638 is recommended for the HDPE

and LLDPE sheets, while ASTM D-882 and

ASTM D-751 are recommended for PVC and

CSPE geomembranes, respectively.10 Puncture

resistance testing is typically recommended

for HDPE and LLDPE geomembranes using

ASTM D-4833.11 To evaluate tear resistance

for HDPE, LLDPE, and PVC geomembrane

Protecting Ground Water—Designing and Installing Liners

7B-13

8 ASTM D-5199, Standard Test Method for Measuring Nominal Thickness of Geotextiles and

Geomembranes.

9 ASTM D-5994, Measuring Core Thickness of Textured Geomembranes.

10 ASTM D-638, Standard Test Method for Tensile Properties of Plastics.

ASTM D-882, Standard Test Methods for Tensile Properties of Thin Plastic Sheeting.

ASTM D-751, Standard Test Methods for Coated Fabrics.

11 ASTM D-4833, Standard Test Method for Index Puncture Resistance of Geotextiles, Geomembranes,

and Related Products.
liners, the recommended testing method is

ASTM D-1004, Die C.12 For CSPE-R

geomembranes, ply adhesion is more of a

concern than tear or puncture resistance and

can be evaluated using ASTM D-413,

Machine Method, Type A.13

Test strips. In preparation for liner placement and field seaming, you should develop

test strips and trial seams as part of the construction process. Construction of such samples should be performed in a manner that

reproduces all aspects of field production.

Providing an opportunity to test seaming

methods and workmanship helps ensure that

the quality of the seams remains constant

and meets specifications throughout the

entire seaming process. 

Temperature Effects 

Liner material properties can be altered by

extreme temperatures. High temperatures can

cause geomembrane liner surfaces to stick

together, a process commonly referred to as

blocking. On the other hand, low temperature can cause the liner to crack when

unrolled or unfolded. Recommended maximum and minimum allowable sheet temperatures for unrolling or unfolding geomembrane

liners are 50°C (122°F) and 0°C (32°F),

respectively. In addition to sticking and cracking, extreme temperatures can cause geomembranes to contract or expand. Polyethylene

geomembranes expand when heated and contract when cooled. Other geomembranes can

contract slightly when heated. Those responsible for placing the liner should take temperature effects into account as they place, seam,

and backfill in the field. 

Wind Effects

It is recommended that you take measures

to protect geomembrane liners from wind

damage. Windy conditions can increase the

potential for tearing as a result of uplift. If

wind uplift is a potential problem, panels can

be weighted down with sand bags.

Seaming Processes

Once panels or rolls have been placed,

another critical step involves field-seaming

the separate panels or rolls together. The

selected seaming process, such as thermal or

chemical seaming, will depend on the chemical composition of the liner. To ensure the

integrity of the seam, you should use the

seaming method recommended by the manufacturer. Thermal seaming uses heat to bond

together the geomembrane panels. Examples

of thermal seaming processes include extrusion welding and thermal fusion (or melt

bonding). Chemical seaming involves the use

of solvents, cement, or an adhesive. Chemical

seaming processes include chemical fusion

and adhesive seaming. For more information

on seaming methods, Technical Guidance

Document: Inspection Techniques for the

Fabrication of Geomembrane Field Seams (U.S.

EPA, 1991c), contains a full chapter on each

of the traditional seaming methods and additional discussion of emerging techniques,

such as ultrasonic, electrical conduction, and

magnetic energy source methods.

Consistent quality in fabricating field

seams is paramount to liner performance.

Conditions that could affect seaming should

be monitored and controlled during installation. Factors influencing seam construction

and performance include: ambient temperature, relative humidity, wind uplift, changes

in geomembrane temperature, subsurface

water content, type of supporting surface

used, skill of the seaming crew, quality and

consistency of chemical or welding materials,

preparation of liner surfaces to be joined,

moisture at the seam interface, and cleanliness of the seam interface. 

7B-14

12 ASTM D-1004, Standard Test Method for Initial Tear Resistance of Plastic Film and Sheeting.

13 ASTM D-413, Standard Test Methods for Rubber Property-Adhesion to Flexible Substrate.

Protecting Ground Water—Designing and Installing Liners 
To help control some of these factors, no

more than the amount of sheeting that can be

used during a shift or a work day should be

deployed at one time. To prevent erosion of

the underlying soil surface or washout of the

geomembrane, proper storm water control

measures should be employed. Ambient temperature can become a concern, if the

geomembrane liner has a high percentage of

carbon black. Although the carbon black will

help to prevent damage resulting from ultraviolet radiation, because its dark color

absorbs heat, it can increase the ambient temperature of the geomembrane, making installation more complicated. To avoid surface

moisture or high subsurface water content,

geomembranes should not be deployed when

the subgrade is wet.

Regardless of how well a geomembrane

liner is designed, its ability to meet performance standards depends on proper quality

assurance and quality control during installation. Geomembrane sheets and seams are

subject to tearing and puncture during installation; punctures or tears can result from contact with jagged edges or underlying materials

or by applying stresses greater than the

geomembrane sheet can handle. Proper quality assurance and quality control can help

minimize the occurrence of pinhole or seam

leaks. For example, properly preparing the

underlying layer and ensuring that the gravel

is of an acceptable size reduces the potential

for punctures. 

Protection and Backfilling

Geomembrane liners that can be damaged

by exposure to weather or work activities

should be covered with a layer of soil or a

geosynthetic as soon as possible after quality

assurance activities associated with geomembrane testing are completed. If the backfill

layer is a soil material, it will typically be a

drainage material like sand or gravel. If the

cover layer is a geosynthetic, it will typically

be a geonet or geocomposite drain placed

directly over the geomembrane. Careful

placement of backfill materials is critical to

avoid puncturing or tearing the geomembrane material.

For soil covers, three considerations determine the amount of slack to be placed in the

underlying geomembrane. These considerations include selecting the appropriate type of

soil, using the proper type of equipment, and

establishing a placement procedure for the

soil. When selecting a soil for backfilling,

characteristics to consider include particle

size, hardness, and angularity, as each of these

can affect the potential for tearing or puncturing the liner. To prevent wrinkling, soil covers

should be placed over the geomembrane in

such a way that construction vehicles do not

drive directly on the liner. Care should be

taken not to push heavy loads of soil over the

geomembrane in a continuous manner.

Forward pushing can cause localized wrinkles

to develop and overturn in the direction of

movement. Overturned wrinkles create sharp

creases and localized stress in the liner and

can lead to premature failure. A recommended method for placing soil involves continually placing small amounts of soil or drainage

material and working outward over the toe of

the previously placed material. 

Another recommended method involves

placing soil over the liner with a large backhoe and spreading it with a bulldozer or similar equipment. If a predetermined amount of

slack is to be placed in the geomembrane, the

temperature of the liner becomes an important factor, as it will effect the ability of the

liner to contract and expand. Although the

recommended methods for covering

geomembrane liners with soil can take more

time than backfilling with larger amounts of

soil, these methods are designed to prevent

damage caused by covering the liner with too

Protecting Ground Water—Designing and Installing Liners

7B-15
much soil too quickly. In the long run, preventing premature liner failure can be faster

and more cost-effective than having to repair

a damaged liner. 

The types of geosynthetics that are often

used as protective covering include geotextiles and geonets. Geogrids and drainage geocomposites can be used for cover soil

reinforcement on slopes. The appendix at the

end of this chapter provides additional information on geosynthetic materials. For

geosynthetic protective covers, as with soil

backfilling, to prevent tearing or puncturing,

most construction vehicles should not be

permitted to move directly on the geomembrane. Some possible exceptions include

small, 4-wheel, all terrain vehicles or other

types of low ground pressure equipment.

Even with these types of vehicles, drivers

should take extreme care to avoid movements, such as sudden starts, stops, and

turns, which can damage the geomembrane.

Seaming-related equipment should be

allowed on the geomembrane liner, as long as

it does not damage the liner. Geosynthetic

materials are placed directly on the liner and

are not bonded to it.

Testing During Construction

Testing during construction enables assessment of the integrity of the seams connecting

the geomembrane panels. Tests performed on

the geomembrane seams are categorized as

either destructive or nondestructive.

Destructive testing. Destructive testing

refers to removing a sample from the liner

seam or sheet and performing tests on the

sample. For liner seams, destructive testing

includes shear testing and peel testing; for

liner sheets, it involves tensile testing. While

quality control procedures often require

destructive testing prior to construction, in

order to ensure that the installed seams and

sheets meet performance standards, destructive testing should be performed during construction also. For increased quality assurance, it is recommended that peel and shear

tests on samples from the installed geomembrane be performed by an independent laboratory. Testing methods for shear testing, peel

testing, and tensile testing vary for different

geomembrane liner types.

Determining the number of samples to

take is a difficult step. Taking too few samples results in a poor statistical representation

of the geomembrane quality. On the other

hand, taking too many samples requires

additional costs and increases the potential

for defects. Defects can result from the repair

patches used to cover the areas from which

samples were taken. 

A common sampling strategy is “fixed

increment sampling” where samples are

taken at a fixed increment along the length of

the geomembrane. Increments range from 80

to 300 m (250 to 1,000 ft). The type of

welding, such as extrusion or fusion welding,

used to connect the seams and the type of

geomembrane liner can also help determine

the appropriate sampling interval. For example, extrusion seams on HDPE require grinding prior to welding and if extensive grinding

occurs, the strength of the HDPE might

decrease. In such cases, sampling at closer

intervals, such as 90 to 120 m (300 to 400

ft), might provide a more accurate description of material properties. If the seam is a

dual hot edge seam, both the inner and outer

seams might need to be sampled and tested. 

If test results for the seam or sheet samples

do not meet the acceptance criteria for the

destructive tests, you should continue testing

the area surrounding the rejected sample to

determine the limits of the low quality seam.

Once the area of low quality has been identified, then corrective measures, such as seaming

a cap over the length of the seam or reseaming

the affected area, might be necessary.

7B-16

Protecting Ground Water—Designing and Installing Liners 
Nondestructive testing. Unlike destructive tests, which examine samples taken from

the geomembrane liner in the containment

area, nondestructive tests are designed to

evaluate the integrity of larger portions of

geomembrane seams without removing pieces

of the geomembrane for testing. Common

nondestructive testing methods include: the

probe test, air lance, vacuum box, ultrasonic

methods (pulse echo, shadow, and impedance

planes), electrical spark test, pressurized dual

seam, and electrical resistivity. You should

select the test method most appropriate for

the material and seaming method. If sections

of a seam fail to meet the acceptable criteria

of the appropriate nondestructive test, then

those sections need to be delineated and

patched, reseamed, or retested. If repairing

such sections results in large patches or areas

of reseaming, then destructive test methods

are recommended to verify the integrity of

such pieces. 

C. Geosynthetic Clay Liners

If a risk evaluation recommended the use

of a single liner, another option to consider is

a geosynthetic clay liner (GCL). GCLs are factory-manufactured, hydraulic barriers typically consisting of bentonite clay (or other very

low permeability materials), supported by

geotextiles or geomembranes held together by

needling, stitching, or chemical adhesives.

GCLs can be used to augment or replace

compacted clay liners or geomembranes, or

they can be used in a composite manner to

augment the more traditional compacted clay

or geomembrane materials. GCLs are typically used in areas where clay is not readily

available or where conserving air space is an

important factor. As GCLs do not have the

level of long-term field performance data that

geomembranes or compacted clay liners do,

states might request a demonstration that

performance of the GCL design will be comparable to that of compacted clay or

geomembrane liners.

What are the mass per unit area

and hydraulic conductivity recommendations for geosynthetic clay

liners?

Geosynthetic clay liners are often designed

to perform the same function as compacted

clay and geomembrane liner components. For

geosynthetic clay liners, you should design

for a minimum of 3.7 kg/m2 (0.75 lb/ft2

) dry

weight (oven dried at 105°C) of bentonite

clay with a hydrated hydraulic conductivity

of no more than 5 x 10-9 cm/sec (2 x 10-9

in/sec). It is important to follow manufacturer

specifications for proper GCL installation.

What issues should be considered in the design of a geosynthetic clay liner?

Factors to consider in GCL design are the

specific material properties needed for the

liner and the chemical interaction or compatibility of the waste with the GCL. When considering material properties, it is important to

keep in mind that bentonite has a low shear

strength when it is hydrated. Manufacturers

have developed products designed to increase

shear strength. 

Materials Selection and Properties

For an effective GCL design, material

properties should be clearly defined in the

specifications used during both manufacture

and construction. The properties that should

be specified include: type of bonds, thickness, moisture content, mass per unit area,

shear strength, and tensile strength. Each of

these properties is described below.

Protecting Ground Water—Designing and Installing Liners

7B-17
Type of bonds. Geosynthetic clay liners

are available with a variety of bonding

designs, which include a combination of clay,

adhesives, and geomembranes or geotextiles.

The type of adhesives, geotextiles, and

geomembranes used as components of GCLs

varies widely. One type of available GCL

design uses a bentonite clay mixed with an

adhesive bound on each side by geotextiles.

A variation on this design involves stitching

the upper and lower geotextiles together

through the clay layer. Alternatively, another

option is to use a GCL where geotextiles on

each side of adhesive or nonadhesive bentonite clay are connected by needle punching. A fourth variation uses a clay mixed with

an adhesive bound to a geomembrane on one

side; the geomembrane can be either the

lower or the upper surface. Figure 3 displays

cross section sketches of the four variations

of GCL bonds. While these options describe

GCLs available at the time of this Guide,

emerging technologies in GCL designs

should also be reviewed and considered.

Thickness. The thickness of the various

available GCL products ranges from 4 to 6

mm (160 to 320 mil). Thickness measurements are product dependent. Some GCLs

can be quality controlled for thickness while

others cannot.

Moisture content. GCLs are delivered to

the job site at moisture contents ranging from

5 to 23 percent, referred to as the “dry” state.

GCLs are delivered dry to prevent premature

hydration, which can cause unwanted variations in the thickness of the clay component

as a result of uneven swelling.

Stability and shear strength. GCLs

should be manufactured and selected to meet

the shear strength requirements specified in

design plans. In this context, shear strength

is the ability of two layers to resist forces

moving them in opposite directions. Since

hydrated bentonite clay has low shear

strength, bentonite clay can be placed

between geotextiles and stitch bonded or

needle- punched to provide additional stability. For example, a GCL with geotextiles supported by stitch bonding has greater internal

resistance to shear in the clay layer than a

GCL without any stitching. Needle-punched

GCLs tend to provide greater resistance than

stitch-bonded GCLs and can also provide

increased friction resistance against an

adjoining layer, because they require the use

of nonwoven geotextiles. Increased friction is

an important consideration on side slopes.

Mass per unit area. Mass per unit area

refers to the bentonite content of a GCL. It is

important to distribute bentonite evenly

throughout the GCL in order to meet desired

hydraulic conductivity specifications. All

GCL products available in North America use

a sodium bentonite clay with a mass per unit

area ranging from 3.2 to 6.0 kg/m2 (0.66 to

1.2 lb/ft2

), as manufactured.

Interaction With Waste

During the selection process for a GCL

liner, you should evaluate the chemical compatibility of the liner materials with the types

of waste that are expected to be placed in the

unit. Certain chemicals, such as calcium, can

have an adverse effect on GCLs, resulting in a

loss of liner integrity. Specific information on

GCL compatibilities should be available from

the manufacturer.

What issues should be considered in the construction of a

geosynthetic clay liner?

Prior to and during construction, it is recommended that a qualified professional

should prepare construction specifications for

the GCL. In these specifications, procedures

for shipping and storing materials, as well as

performing acceptance testing on delivered

7B-18

Protecting Ground Water—Designing and Installing Liners 
Protecting Ground Water—Designing and Installing Liners

7B-19

Figure 3

Four Variations of GCL Bonding Methods

Source: U.S. EPA, 1993c.
materials, should be identified. The specifications should also address methods for subgrade preparation, joining panels, repairing

sections, and protective backfilling.

Shipment, Handling, and Site

Storage

GCLs are manufactured in widths of

approximately 2 to 5 m (7 to 17 ft) and

lengths of 30 to 60 m (100 to 200 ft).

Directly after manufacturing, GCLs are rolled

around a core and covered with a thin plastic

protective covering. This waterproof covering

serves to protect the material from premature

hydration. GCLs should be stored at the factory with these protective coverings. Typical

storage lengths range from a few days to 6

months. To ensure protection of the plastic

covering and the rolls themselves during

loading and unloading, it is recommended

that qualified professionals specify the equipment needed at the site to lift and deploy the

rolls properly.

To reduce the potential for accidental

damage or for GCLs to absorb moisture at

the site, you should try to arrange for “justin-time-delivery” for GCLs transported from

the factory to the field. Even with “just-intime-delivery,” it might be necessary to store

GCLs for short periods of time at the site.

Often the rolls can be delivered in trailers,

which can then serve as temporary storage.

To help protect the GCLs prior to deployment, you should use wooden pallets to keep

the rolls off the ground, placing heavy, waterproof tarps over the GCL rolls to protect

them from precipitation, and using sandbags

to help keep the tarps in place.

Manufacturer specifications should also

indicate how high rolls of GCLs can be

stacked horizontally during storage. Overstacking can cause compression of the core

around which the GCL is wrapped. A damaged core makes deployment more difficult

and can lead to other problems. For example,

rolls are sometimes handled by a fork lift

with a stinger attached. The stinger is a long

tapered rod that fits inside the core. If the

core is crushed, the stinger can damage the

liner during deployment.

Acceptance and Conformance

Testing

Acceptance and conformance testing is recommended either upon delivery of the GCL

rolls or at the manufacturer’s facility prior to

delivery. Conformance test samples are used

to ensure that the GCL meets the project

plans and specifications. GCLs should be

rewrapped and replaced in dry storage areas

immediately after test samples are removed.

Liner specifications should prescribe sampling

frequencies based on either total area or on

number of rolls. Since variability in GCLs can

exist between individual rolls, it is important

for acceptance and conformance testing to

account for this. Conformance testing can

include the following.

Mass per unit area test. The purpose of

evaluating mass per unit area is to ensure an

even distribution of bentonite throughout the

GCL panel. Although mass per unit area

varies from manufacturer to manufacturer, a

typical minimum value for oven dry weight

is 3.7 kg/m2 (0.75 lb/ft2

). Mass per unit area

should be tested using ASTM D-5993.14 This

test measures the mass of bentonite per unit

area of GCL. Sampling frequencies should be

determined using ASTM D- 4354.15

Free swell test. Free swell refers to the

ability of the clay to absorb liquid. Either

ASTM D-5890 or GRI-GCL1, a test method

developed by the Geosynthetic Research

Institute, can be used to evaluate the free

swell of the material.16

7B-20

14 ASTM D-5993, Standard Test Method for Measuring Mass per Unit Area of Geosynthetic Clay Liners.

15 ASTM D-4354, Standard Practice for Sampling of Geosynthetics for Testing.

16 ASTM D-5890, Test Method for Swell Index of Clay Mineral Components of Geosynthetic Clay Liners.

GRI-GCL1, Swell Measurement of the Clay Component of Geosynthetic Clay Liners.

Protecting Ground Water—Designing and Installing Liners 
Direct shear test. Shear strength of the

GCLs can be evaluated using ASTM D-5321.17

The sampling frequency for this performanceoriented test is often based on area, such as

one test per 10,000 m2 (100,000 ft2

).

Hydraulic conductivity test. Either ASTM

D-5084 (modified) or GRI-GCL2 will measure the ease with which liquids can move

through the GCL.18

Other tests. Testing of any geotextiles or

geomembranes should be made on the original rolls of the geotextiles or geomembranes

and before they are fabricated into the GCL

product. Once these materials have been

made part of the GCL product, their properties can change as a result of any needling,

stitching, or gluing. Additionally, any peel

tests performed on needle punched or stitch

bonded GCLs should use the modified ASTM

D-413 with a recommended sampling frequency of one test per 2,000 m2 (20,000 ft2

).19

Subgrade Preparation

Because the GCL layer is relatively thin,

the first foot of soil underlying the GCL

should have a hydraulic conductivity of 1 x

10-5 cm/sec or less. Proper subgrade preparation is essential to prevent damage to the

GCL layer as it is installed. This includes

clearing away any roots or large particles that

could potentially puncture the GCL and its

geotextile or geomembrane components. The

soil subgrade should be of the specified grading, moisture content, and density required

by the installer and approved by a construction quality assurance engineer for placement

of the GCL. Construction equipment deploying the rolls should not deform or rut the soil

subgrade excessively. To help ensure this, the

soil subgrade should be smooth rolled with a

smooth-wheel roller and maintained in a

smooth condition prior to deployment.

Joining Panels

GCLs are typically joined by overlapping

panels, without sewing or mechanically connecting pieces together. To ensure proper

joints, you should specify minimum and

maximum overlap distances. Typical overlap

distances range from 150 to 300 mm (6 to 12

in.). For some GCLs, such as needle punched

GCLs with nonwoven geotextiles, it might be

necessary to place bentonite on the area of

overlap. If this is necessary, you should take

steps to prevent fugitive bentonite particles

from coming into contact with the leachate

collection system, as they can cause physical

clogging.

Repair of Sections Damaged During

Liner Placement

During installation, GCLs might incur

some damage to either the clay component or

to any geotextiles or geomembranes. For

damage to geotextile or geomembrane components, repairs include patching using geotextile or geomembrane materials. If the clay

component is disturbed, a patch made from

the same GCL product should be used to perform any repairs. 

Protective Backfilling

As soon as possible after completion of

quality assurance and quality control activities, you should cover GCLs with either a soil

layer or a geosynthetic layer to prevent

hydration. The soil layer can be a compacted

clay liner or a layer of coarse drainage material. The geosynthetic layer is typically a

Protecting Ground Water—Designing and Installing Liners

7B-21

17 ASTM D-5321, Standard Test Method for Determining the Coefficient of Soil and Geosynthetic or

Geosynthetic and Geosynthetic Friction by the Direct Shear Method.

18 ASTM D-5084, Standard Test Method for Measurement of Hydraulic Conductivity of Saturated Porous

Materials Using a Flexible Wall Permeameter.

GRI-GCL2, Permeability of Geosynthetic Clay Liners (GCLs).

19 ASTM D-413, Standard Test Methods for Rubber Property-Adhesion to Flexible Substrate.
geomembrane; however, depending on sitespecific designs, it can be a geotextile. As

noted earlier, premature hydration before

covering can lead to uneven swelling, resulting in a GCL with varied thickness.

Therefore, a GCL should be covered with its

subsequent soil or geosynthetic layer before a

rainfall or snowfall occurs. Premature hydration is less of a concern for GCLs, where the

geosynthetic components are needle punched

or stitch bonded, because these types of connections can better limit clay expansion.

III. Composite

Liners

A composite liner consists of both a

geomembrane liner and natural soil. The

geomembrane forms the upper component

with the natural soil being the lower component. The ususal variations are:

• Geomembrane over compacted clay

liner (GM/CCL).

• Geomembrane over geosynthetic clay

liner (GM/GCL).

• Geomembrane over geosynthetic clay

liner over compacted clay liner

(GM/GCL/CCL).

A composite liner provides an effective

hydraulic barrier by combining the complementary properties of the two different liners

into one system. The geomembrane provides a

highly impermeable layer to maximize leachate

collection and removal. The natural soil liner

serves as a backup in the event of any leakage

from the geomembrane. With a composite

liner design, you should construct a leachate

collection and removal system above the

geomembrane. Information on design and construction of leachate collection and removal

systems is provided in Section V below.

What are the thickness and

hydraulic conductivity recommendations for composite liners?

Each component of the composite liner

should follow the recommendations for

geomembranes, geosynthetic clay liners, and

compacted clay liners described earlier.

Geomembrane liners should have a minimum thickness of 30 mil, except for HDPE

liners, which should have a minimum thickness of 60 mil. Similarly, compacted clay liners should be at least 2 feet thick and are

typically 2 to 5 feet thick. For compacted

clay liners and geosynthetic clay liners, you

should use materials with maximum

hydraulic conductivities of 1 x 10-7 cm/sec (4

x 10-8 in/sec) and 5 x 10-9 cm/sec (2 x 10-9

in/sec), respectively.

What issues should be considered in the design of a composite liner?

As a starting point, you should follow the

design considerations discussed previously for

single liners. In addition, to achieve the benefits of a combined liner system, you should

install the geomembrane to ensure good contact with the compacted clay layer. The uniformity of contact between the geomembrane

and the compacted clay layer helps control

the flow of leachate. Porous material, such as

drainage sand or a geonet, should not be

placed between the geomembrane and the

clay layer. Porous materials will create a layer

of higher hydraulic conductivity, which will

increase the amount of leakage below any

geomembrane imperfection.

You should consider the friction or shear

strength between a compacted clay layer and

a geomembrane. The friction or shear stress

at this surface is often low and can form a

weak plane on which sliding can occur.

7B-22

Protecting Ground Water—Designing and Installing Liners 
ASTM D-5321 provides a test method for

determining the friction coefficient of soil and

geomembranes.20 When using bentoniteamended soils, it is important to account for

how the percentage of bentonite added and

the degree of saturation affect interface friction. To provide for stable slopes, it is important to control both the bentonite and

moisture contents. A textured geomembrane

can increase the friction with the clay layer

and improve stability. 

What issues should be considered in the construction of a

composite liner?

To achieve good composite bonding, the

geomembrane and the compacted clay layer

should have good hydraulic contact. To

improve good contact, you should smoothroll the surface of the compacted clay layer

using a smooth, steel-drummed roller and

remove any stones. In addition, you should

place and backfill the geomembrane so as to

minimize wrinkles.

The placement of geomembranes onto a

compacted clay layer poses a challenge,

because workers cannot drive heavy

machines over the clay surface without

potentially damaging the compacted clay

component. Even inappropriate footwear can

leave imprints in the clay layer. It might be

possible to drive some types of low ground

pressure equipment or small, 4-wheel, all terrain vehicles over the clay surface, but drivers

should take extreme care to avoid movements, such as sudden starts, stops, and

turns, that could damage the surface. To

avoid damaging the clay layer, it is recommended that you unroll geomembranes by

lifting the rolls onto jacks at a cell side and

pulling down on the geomembrane manually.

Also, the entire roll with its core can be

unrolled onto the cell (with auxiliary support

using ropes on embankments). 

To minimize desiccation of the compacted

clay layer, you should place the geomembrane over the clay layer as soon as possible.

Additional cover materials should also be

placed over the geomembrane. Exposed

geomembranes absorb heat, and high temperatures can dry out and crack an underlying

compacted clay layer. Daily cyclic changes in

temperature can draw water from the clay

layer and cause this water to condense on the

underside of the geomembrane. This withdrawal of water can lead to desiccation cracking and potential interface stability concerns. 

IV. Double Liners

(Primary and

Secondary Lined

Systems)

In a double-lined waste management unit,

there are two distinct liners—one primary

(top) liner and one secondary (bottom) liner.

Each liner might consist of compacted clay, a

geomembrane, or a composite (consisting of a

geomembrane and a compacted clay layer or

GCL). Above the primary liner, it is recommended that you construct a leachate collection and removal system to collect and convey

liquids out of the waste management unit and

to control the depth of liquids above the primary liner. In addition, you should place a

leak detection, collection, and removal system

between the primary and secondary liner.

This leak detection system will provide leak

warning, as well as collect and remove any

liquid or leachate that has escaped the primary liner. See section V below for information

on the design of leachate collection and

removal systems and leak detection, collection, and removal systems.

Protecting Ground Water—Designing and Installing Liners

7B-23

20 ASTM D-5321, Standard Test Method for Determining the Coefficient of Soil and Geosynthetic or

Geosynthetic and Geosynthetic Friction by the Direct Shear Method.
What are the thickness and

hydraulic conductivity recommendations for double liners?

Each component of the double liner

should follow the recommendations for

geomembranes, compacted clay liners, or

composite liners described earlier.

Geomembrane liners should have a minimum

thickness of 30 mil, except for HDPE liners,

which should have a minimum thickness of

60 mil. Similarly, compacted clay liners

should be at least 2 feet thick and are typically 2 to 5 feet thick. For compacted clay liners

and geosynthetic clay liners, use materials

with maximum hydraulic conductivities of 1

x 10-7 cm/sec (4 x 10-8 in/sec) and 5 x 10-9

cm/sec (2 x 10-9 in/sec), respectively.

What issues should be considered in the design and construction of a double liner?

Like composite liners, double liners are

composed of a combination of single liners.

When planning to design and construct a

double liner, you should consult the sections

on composite and single liners first. In addition, you should consult the sections on

leachate collection and removal systems and

leak detection systems.

V. Leachate

Collection and

Leak Detection

Systems

One of the most important functions of a

waste management unit is controlling

leachate and preventing contamination of the

underlying ground water. Both leachate collection and removal systems and leak detection systems serve this purpose. You should

consult with the state agency too determine if

such systems are required. The primary function of a leachate collection and removal system is to collect and convey leachate out of a

unit and to control the depth of leachate

above a liner. The primary function of a leak

detection system is to detect leachate that has

escaped the primary liner. A leak detection

system refers to drainage material located

below the primary liner and above a secondary liner (if there is one); it acts as a secondary leachate collection and removal

system. After the leachate has been removed

and collected, a leachate treatment system

might be incorporated to process the leachate

and remove harmful constituents.

The information in this section on leachate

collection and leak detection systems is

applicable if the unit is a landfill or a waste

pile. Surface impoundments, which manage

liquid wastes, usually will not have leachate

collection and removal systems unless they

will be closed in-place as landfills; they might

have leak detection systems to detect liquid

wastes that have escaped the primary liner.

Leachate collection or leak detection systems

generally are not used with land application.

A. Leachate Collection

System

A typical leachate collection system

includes a drainage layer, collection pipes, a

removal system, and a protective filter layer.

Leachate collection systems are designed to

collect leachate for treatment or alternate disposal and to reduce the buildup of leachate

above the liner system. Figure 4 shows a

cross section of a typical leachate collection

system showing access to pipes for cleaning.

7B-24

Protecting Ground Water—Designing and Installing Liners 
What are the recommendations

for leachate collection and

removal systems?

You should design a leachate collection and

removal system to maintain less than 30 cm

(12 in.) depth of leachate, or “head,” above

the liner if granular soil or a geosynthetic

material is used. The reason for maintaining

this level is to prevent excessive leachate from

building up above the liner, which could

jeopardize the liner’s performance. This

should be the underlying factor guiding the

design, construction, and operation of the

leachate collection and removal system.

You should design a leachate collection

and removal system capable of controlling the

estimated volume of leachate. To determine

potential leachate generation, you should use

water balance equations or models. The most

commonly used method to estimate leachate

generation is EPA’s Hydrogeologic Evaluation

of Landfill Performance (HELP) model.21 This

model uses weather, soil, and waste management unit design data to determine leachate

generation rates.

What issues should be considered in the design of a leachate

collection and removal system?

You should design a leachate collection

and removal system to include the following

elements: a low-permeability base, a highpermeability drainage layer, perforated

leachate collection pipes, a protective filter

layer, and a leachate removal system. During

Protecting Ground Water—Designing and Installing Liners

7B-25

21 Available on the CD-ROM version of the Guide, as well as from the U.S. Army Corps of Engineers Web

site <www.wes.army.mil/el/elmodels/index.html#landfill>

Source: U.S. EPA, 1995b

Figure 4

Typical Leachate Collection System
design, you should consider the stability of

the base, the transmissivity of the drainage

layers, and the strength of the collection

pipes. It is also prudent to consider methods

to minimize physical, biological, and chemical clogging within the system.

Low-Permeability Base

A leachate collection system is placed over

the unit’s liner system. The bottom liner

should have a minimum slope of 2 percent to

allow the leachate collection system to gravity

flow to a collection sump. This grade is necessary to provide proper leachate drainage

throughout the operation, closure, and postclosure of the unit. Estimates of foundation

soil settlement should include this 2 percent

grade as a post-settlement design.

High-Permeability Drainage Layer

A high-permeability drainage layer consists

of drainage materials placed directly over the

low-permeability base, at the same minimum

2 percent grade. The drainage materials can

be either granular soil or geosynthetic materials. For soil drainage materials, a maximum of

12 inches of materials with a hydraulic conductivity of at least 1 x 10-2 cm/sec (4 x 10-3

in/sec) is recommended. For this reason, sand

and gravel are the most common soil materials used. If the drainage layer is going to

incorporate sand or gravel, it should be

demonstrated that the layer will have sufficient bearing capacity to withstand the waste

load of the full unit. Additionally, if the waste

management unit is designed on grades of 15

percent or higher, it should be demonstrated

that the soil drainage materials will be stable

on the steepest slope in the design.

Geosynthetic drainage materials such as

geonets can be used in addition to, or in place

of, soil materials. Geonets promote rapid

transmission of liquids and are most effective

when used in conjunction with a filter layer

or geotextile to prevent clogging. Geonets

consist of integrally connected parallel sets of

plastic ribs overlying similar sets at various

angles. Geonets are often used on the side

walls of waste management units because of

their ease of installation. Figure 5 depicts a

typical geonet material configuration.

The most critical factor involved with using

geonets in a high-permeability drainage layer

is the material’s ability to transmit fluids

under load. The flow rate of a geonet can be

evaluated by ASTM D-4716.22 Several additional measures for determining the transmissivity of geonets are discussed in the Solid

Waste Disposal Facility Criteria: Technical

Manual (U.S. EPA, 1993b).

Perforated Leachate Collection Pipes

Whenever the leachate collection system is

a natural soil, a perforated piping system

should be located within it to rapidly transmit the leachate to a sump and removal system. Through the piping system, leachate

flows gravitationally to a low point where the

sump and removal system is located. The

design of perforated leachate collection pipes,

therefore, should consider necessary flow

rates, pipe sizing, and pipe structural

strength. After estimating the amount of

leachate using the HELP model or a similar

water balance model, it is possible to calculate the appropriate pipe diameter and spacing. For the leachate collection system

design, you should select piping material that

can withstand the anticipated weight of the

waste, construction and operating equipment

stresses, and foundation settling. Most

leachate collection pipes used in modern

waste management units are constructed of

HDPE. HDPE pipes provide great structural

strength, while allowing significant chemical

resistance to the many constituents found in

leachate. PVC pipes are also used in waste

7B-26

22 ASTM D-4716, Standard Test Method for Constant Head Hydraulic Transmissivity (In-Plane Flow) of

Geotextiles and Geotextile Related Products.

Protecting Ground Water—Designing and Installing Liners 
management units, but they are not as chemically resistant as HDPE pipes. 

Protective Filter Layer

To protect the drainage layer and perforated leachate collection piping from clogging,

you should place a filter layer over the highpermeability drainage layer. To prevent waste

material from moving into the drainage layer,

the filter layer should consist of a material

with smaller pore space than the drainage

layer materials or the perforation openings in

the collection pipes. Sand and geotextiles are

the two most common materials used for filtration. You should select sand that allows

adequate flow of liquids, prevents migration

of overlying solids or soils into the drainage

layer, and minimizes clogging during the service life. In designing the sand filter, you

should consider particle size and hydraulic

conductivity. The advantages of using sand

materials include common usage, traditional

design, and durability.

Any evaluation of geotextile materials

should address the same concerns but with a

few differences. To begin with, the average

pore size of the geotextile should be large

enough to allow the finer soil particles to pass

but small enough to

retain larger soil particles. The number of

openings in the geotextile should be large

enough that, even if

some of the openings

clog, the remaining

openings will be sufficient to pass the design

flow rate. In addition to

pore size, geotextile filter specifications should

include durability

requirements. The

advantages of geotextile

materials include vertical space savings and

easy placement. Chapter 5 of Technical

Guidance Document: Quality Assurance and

Quality Control for Waste Containment Facilities

(U.S. EPA, 1993c) offers guidance on protection of drainage layers.

Leachate Removal System

Leachate removal often involves housing a

sump within the leachate collection drainage

layer. A sump is a low point in the liner constructed to collect leachate. Modern waste

management unit sumps often consist of prefabricated polyethylene structures supported

on a steel plate above the liner. Especially

with geomembrane liners, the steel plate

serves to support the weight of the sump and

protect the liner from puncture. Gravel filled

earthen depressions can serve as the sump.

Reinforced concrete pipe and concrete flooring also can be used in place of the polyethylene structure but are considerably heavier.

To remove leachate that has collected in

the sump, you should use a submersible

pump. Ideally, the sump should be placed at

a depth of 1 to 1.5 m (3 to 5 ft) to allow

enough leachate collection to prevent the

pump from running dry. You should consider

Protecting Ground Water—Designing and Installing Liners

7B-27

Figure 5

Typical Geonet Configuration
installing a level control, backup pump, and

warning system to ensure proper sump operation. Also consider using a backup pump as

an alternate to the primary pump and to

assist it during high flow periods. A warning

system should be used to indicate pump malfunction.

Standpipes, vertical pipes extending

through the waste and cover system, offer

one method of removing leachate from a

sump without puncturing the liner.

Alternatively, you can remove leachate from a

sump using pipes that are designed to penetrate the liner. When installing pipe penetrations through the liner, you should proceed

with extreme caution to prevent any liner

damage that could result in uncontained

leachate. Both of these options rely on gravity

to direct leachate to a leachate collection

pond or to an external pumping station.

Minimizing Clogging

Leachate collection and removal systems

are susceptible to physical, biological, and

chemical clogging. Physical clogging can

occur through the migration of finer-grained

materials into coarser-grained materials, thus

reducing the hydraulic conductivity of the

coarser-grained material. Biological clogging

can occur through bacterial growth in the

system due to the organic and nutrient materials in leachate. Chemical clogging can be

caused by chemical precipitates, such as calcium carbonates, causing blockage or cementation of granular drainage material.

Proper selection of drainage and filter materials is essential to minimize clogging in the

high-permeability drainage layer. Soil and geotextile filters can be used to minimize physical

clogging of both granular drainage material

and leachate collection pipes. When placed

above granular drainage material, these filters

can also double as an operations layer to prevent sharp waste from damaging the liner or

leachate collection and removal systems. To

minimize chemical and biological clogging for

granular drainage material, the best procedure

is to keep the interstices of the granular

drainage material as open as possible.

The leachate collection pipes are also susceptible to similar clogging. To prevent this,

you should incorporate measures into the

design to allow for routine pipe cleaning,

using either mechanical or hydraulic methods. The cleaning components can include

pipes with a 15 cm (6 in) minimum diameter

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 cleaning solutions. Also, you should

check that the design does not include wrapping perforated leachate collection pipes

directly with geotextile filters. If the geotextile becomes clogged, it can block flow into

the pipe.

B. Leak Detection System

The leak detection system (LDS) is also

known as the secondary leachate collection

and removal system. It uses the same

drainage and collection components as the

primary leachate collection and removal system and identifies, collects, and removes any

leakage from the primary system. The LDS

should be located directly below the primary

liner and above the secondary liner.

What are the recommendations

for leak detection systems?

The LDS should be designed to assess the

adequacy of the primary liner against

leachate leakage; it should cover both the

bottom and side walls of a waste management unit. The LDS should be designed to

collect leakage through the primary layer and

transport it to a sump within 24 hours.

7B-28

Protecting Ground Water—Designing and Installing Liners 
The LDS should allow for monitoring and

collection of leachate escaping the primary

liner system. You should monitor the LDS on

a regular basis. If the volume of leachate

detected by the LDS appears to be increasing

or is significant, you should consider a closer

examination to determine possible remediation measures. A good rule of thumb is that if

the LDS indicates a seepage level greater than

20 gallons per acre per day, the system might

need closer monitoring or remediation.

C. Leachate Treatment

System

Once the leachate has been removed from

the unit and collected, you should consider

taking measures to characterize the leachate

in order to ensure proper management. There

are several methods of disposal for leachate,

and the treatment strategy will vary according

to the disposal method chosen. Leachate disposal options include discharging to or

pumping and hauling to a publicly owned

treatment works or to an onsite treatment

system; treating and discharging to the environment; land application; and natural or

mechanical evaporation.

When discharging to or pumping and

hauling leachate to a publicly owned treatment works, a typical treatment strategy

includes pretreatment. Pretreatment could

involve equalization, aeration, sedimentation,

pH adjustment, or metals removal.23 If the

plan for leachate disposal does not involve a

remote treatment facility, pretreatment alone

usually is not sufficient.

There are two categories of leachate treatment, biological and physical/chemical. The

most common method of biological treatment

is activated sludge. Activated sludge is a “suspended-growth process that uses aerobic

microorganisms to biodegrade organic contaminants in leachate.”24 Among physical/chemical

treatment techniques, the carbon absorption

process and reverse osmosis are the two most

common methods. Carbon absorption uses

carbon to remove dissolved organics from

leachate and is very expensive. Reverse osmosis involves feeding leachate into a tubular

chamber whose wall acts as a synthetic membrane, allowing water molecules to pass

through but not pollutant molecules, thereby

separating clean water from waste constituents.

What are the recommendations

for leachate treatment systems?

You should review all applicable federal

and state regulations and discharge standards

to determine which treatment system will

ensure long-term compliance and flexibility

for the unit. Site-specific factors will also play

a fundamental role in determining the proper

leachate treatment system. For some facilities,

onsite storage and treatment might not be an

option due to space constraints. For other

facilities, having a nearby, publicly owned

treatment works might make pretreatment

and discharge to the treatment works an

attractive alternative.

VI. Construction

Quality

Assurance and

Quality Control

Even the best unit design will not translate

into a structure that is protective of human

health and the environment, if the unit is not

properly constructed. Manufacturing quality

assurance and manufacturing quality control

(MQA and MQC) are also important issues

for the overall project; however, they are discussed only briefly here since they are primarily the responsibility of a manufacturer.

Nonetheless, it is best to select a manufacturProtecting Ground Water—Designing and Installing Liners

7B-29

23 Arts, Tom. “Alternative Approaches For Leachate Treatment.” World Wastes.

24 Ibid.
er who incorporates appropriate quality

assurance and quality control (QA and QC)

mechanisms as part of the manufacturing

process. The remainder of this section provides a general description of the components of a construction quality assurance and

construction quality control (CQA and CQC)

program for a project. CQA and CQC are

critical factors for waste management units.

They are not interchangeable, and the distinction between them should be kept in

mind when preparing plans. CQA is third

party verification of quality, while CQC consists of in-process measures taken by the contractor or installer to maintain quality. You

should establish clear protocols for identifying and addressing issues of concern

throughout every stage of construction.

What is manufacturing quality

assurance?

The desired characteristics of liner materials should be specified in the unit’s contract

with the manufacturer. The manufacturer

should be responsible for certifying that materials delivered conform to those specifications.

MQC implemented to ensure such conformance might take the form of process quality

control or computer-aided quality control. If

requested, the manufacturer should provide

information on the MQC measures used,

allow unit personnel or engineers to visit the

manufacturing facility, and provide liner samples for testing. It is good practice for the

manufacturer to have a dedicated individual

in charge of MQC who would work with unit

personnel in these areas.

What is construction quality

assurance?

CQA is a verification tool employed by the

facility manager or regulatory agency, consisting of a planned series of observations and

tests designed to ensure that the final product meets project specifications. CQA testing,

often referred to as acceptance inspection,

provides a measure of the final product quality and its conformance with project plans

and specifications. Performing acceptance

inspections routinely, as portions of the project become complete, allows early detection

and correction of deficiencies, before they

become large and costly.

On routine construction projects, CQA is

normally the concern of the facility manager

and is usually performed by an independent,

third-party testing firm. The independence of

the testing firm is important, particularly

when a facility manager has the capacity to

perform the CQA activities. Although the

7B-30

Protecting Ground Water—Designing and Installing Liners 

MQC, MQA, CQC, and CQA

Manufacturing quality control

(MQC) is measures taken by the manufacturer to ensure compliance with the

material and workmanship specifications

of the facility manager.

Manufacturer quality assurance

(MQA) is measures taken by facility personnel, or by an impartial party brought

in expressly for the purpose, to determine if the manufacturer is in compliance with the specifications of the facility

manager.

Construction quality control (CQC)

is measures taken by the installer or contractor to ensure compliance with the

installation specifications of the facility

manager.

Construction quality assurance

(CQA) is measures taken by facility personnel, or by an impartial party brought

in expressly for the purpose, to determine if the installer or contractor is in

compliance with the installation specifications of the facility manager.
facility’s in-house CQA personnel might be

registered professional engineers, a perception

of misrepresentation might arise if CQA is not

performed by an independent third party.

The independent party should designate a

CQA officer and fully disclose any activities

or relationships that the officer has with the

facility manager that might impact his or her

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. State regulatory representatives

can help evaluate whether these mechanisms

are sufficient to ensure acceptable CQA.

What is construction quality 

control?

CQC is an ongoing process of measuring

and controlling the characteristics of the product in order to meet manufacturer’s or project

specifications. CQC inspections are typically

performed by the contractor to provide an inprocess 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. Since CQC is a production

tool employed by the manufacturer of materials and by the contractor installing the materials at the site, the Guide does not cover CQC

in detail. CQC is performed independently of

CQA. For example, while a geomembrane

liner installer will perform CQC testing of

field seams, the CQA program should require

independent testing of those same seams by a

third-party inspector.

How can implementation of CQA

and CQC plans be ensured?

When preparing to design and construct a

waste management unit, regardless of design,

you should develop CQA and CQC plans

customized to the project. To help the project

run smoothly, the CQA plan should be easy

to follow. You should organize the CQA plan

to reflect the sequence of construction and

write it in language that will be familiar to an

average field technician. For a more detailed

discussion of specific CQA and CQC activities recommended for each type of waste

management unit, you should consult

Technical Guidance Document: Quality

Assurance and Quality Control for Waste

Management Containment Facilities (U.S. EPA,

1993c). This document provides information

to develop comprehensive QA plans and to

carry out QC procedures at waste management units. 

CQA and CQC plans can be implemented

through a series of meetings and inspections,

which should be documented thoroughly.

Communication among all parties involved in

design and construction of a waste management unit is essential to ensuring a quality

product. You should define responsibility and

authority in written QA and QC plans and

ensure that each party involved understands

its role. Pre-construction meetings are one

way to help clarify roles and responsibilities.

During construction, meetings can continue

to be useful to help resolve misunderstandings

and to identify solutions to unanticipated

problems that might develop. Some examples

of typical meetings during the course of any

construction project include pre-bid meetings,

resolution meetings, pre-construction meetings, and progress meetings.

Protecting Ground Water—Designing and Installing Liners

7B-31
A. Compacted Clay Liner

Quality Assurance and

Quality Control

Although manufacturing quality control

and quality assurance are often the responsibility of the materials manufacturer, in the

case of soil components, manufacturing and

construction quality control testing can be

the responsibility of the facility manager. The

CQA and CQC plans should specify procedures for quality assurance and quality control during construction of the compacted

clay liners.

How can implementation of QA

and QC be ensured for a compacted clay liner?

QC testing is typically performed by the

contractor on materials used in construction

of the liner. This testing examines material

properties such as moisture content, soil density, Atterberg limits, grain size, and laboratory hydraulic conductivity. Additional testing

of soil moisture content, density, lift thickness, and hydraulic conductivity helps ensure

that the waste management unit has been

constructed in accordance with the plans and

technical specifications.

CQA testing for soil liners includes the

same tests described for QC testing in the

paragraph above. Generally, the tests are performed less frequently. CQA testing is performed by an individual or an entity

independent of the contractor. Activities of

the CQA officer are essential to document

quality of construction. The responsibilities

of the CQA officer and his or her staff might

include communicating with the contractor;

interpreting and clarifying project drawings

and specifications with the designer, facility

manager, and contractor; recommending

acceptance or rejection by the facility manager of work completed by the construction

contractor; and submitting blind samples,

such as duplicates and blanks, for analysis by

the contractor’s testing staff or independent

laboratories.

You should also consider constructing a

test pad prior to full-scale construction as a

CQA tool. As described earlier in the section

on compacted clay liners, pilot construction

or test fill of a small-scale test pad 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. 

Specific factors to examine or test during

construction of a test fill include: preparation

and compaction of foundation material to the

required bearing strength; methods of controlling uniformity of the soil material; compactive effort, such as type of equipment and

number of passes needed to achieve required

soil density and hydraulic conductivity; and

lift thickness and placement procedures

needed to achieve uniformity of density

throughout a lift and prevent boundary

effects between lifts or between placements in

the same lift. Test pads can also provide a

means to evaluate the ability of different

types of soil to meet hydraulic conductivity

requirements in the field. In addition to

allowing an opportunity to evaluate material

performance, test pads also allow evaluation

of the skill and competence of the construction team, including equipment operators

and QC specialists.

B. Geomembrane Liner

Quality Assurance and

Quality Control

As with the construction of soil liners,

installation of geomembrane liners should be

in conformance with a CQA and CQC plan.

The responsibilities of the CQA personnel for

the installation of the geomembrane are gen7B-32

Protecting Ground Water—Designing and Installing Liners 
erally the same as the responsibilities for the

construction of a compacted clay liner, with

the addition of certain activities including

observations of the liner storage area and liners in storage, and handling of the liner as the

panels are positioned in the cell.

Geomembrane CQA staff should also observe

seam preparation, seam overlap, and materials underlying the liner.

How can implementation of QA

and QC be ensured for a

geomembrane liner?

Prior to installation, you should work with

the geomembrane manufacturer to ensure the

labeling system for the geomembrane rolls is

clear and logical, allowing easy tracking of the

placement of the rolls within the unit. It is

important to examine the subgrade surface

with both the subgrade contractor and the liner

installer to ensure it conforms to specifications.

Once liner installation is underway, CQA

staff might be responsible for observations of

destructive testing conducted on scrap test

welds prior to seaming. Geomembrane CQA

staff might also be responsible for sending

destructive seam sampling to an independent

testing laboratory and reviewing the results for

conformance to specifications. Other observations for which the CQA staff are typically

responsible include observations of all seams

and panels for defects due to manufacturing

and handling, and placement and observations

of all pipe penetrations through a liner. 

Test methods, test parameters, and testing

frequencies should be specified in the CQA

plan to provide context for any data collected. It is prudent to allow for testing frequency to change, based on the performance of

the geomembrane installer. If test results indicate poor workmanship, you should increase

testing. If test results indicate high quality

installation work, you can consider reducing

testing frequencies. When varying testing frequency, you should establish well-defined

procedures for modifying testing frequency. It

is also important to evaluate testing methods,

understand the differences among testing

methods, and request those methods appropriate for the material and seaming method

be used. Nondestructive testing methods are

preferrable when possible to help reduce the

number of holes cut into the geomembrane.

Geomembrane CQA staff also should document the results of their observations and prepare reports indicating the types of sampling

conducted and sampling results, locations of

destructive samples, locations of patches,

locations of seams constructed, and any problems encountered. In some cases, they might

need to prepare drawings of the liner installation. Record drawing preparation is frequently

assigned to the contractor, to a representative

of the facility manager, or to the engineer. You

should request complete reports from any

CQA staff and the installers. To ensure complete CQA documentation, it is important to

maintain daily CQA reports and prepare

weekly summaries.

C. Geosynthetic Clay Liner

Quality Assurance and

Quality Control

Construction quality assurance for geosynthetic clay liners is still a developing area; the

GCL industry is continuing to establish standardized quality assurance and quality control procedures. The CQA recommendation

for GCLs can serve as a starting point. You

should check with the GCL manufacturer and

installer for more specific information.

Protecting Ground Water—Designing and Installing Liners

7B-33
How can implementation of QA

and QC be ensured for a geosynthetic clay liner?

It is recommended that you develop a

detailed CQA plan, including product specifications; shipping, handling, and storage

procedures; seaming methods; and placement

of overlying material. It is important to work

with the manufacturer to verify that the

product meets specifications. Upon receipt of

the GCL product, you should also verify that

it has arrived in good condition.

During construction, CQA staff should

ensure that seams are overlapped properly

and conform to specifications. CQA staff

should also check that panels, not deployed

within a short period of time, are stored

properly. In addition, as overlying material is

placed on the GCL, it is important to restrict

vehicle traffic directly on the GCL. You

should prohibit direct vehicle traffic, with the

exception of small, 4-wheel, all terrain vehicles. Even with the small all-terrain vehicles,

drivers should take extreme care to avoid

movements, such as sudden starts, stops, and

turns, which can damage the GCL. 

As part of the CQA documentation, it is

important to maintain records of weather

conditions, subgrade conditions, and GCL

panel locations. Also, you should document

any repairs that were necessary or other

problems identified and addressed.

D. Leachate Collection

System Quality

Assurance and Quality

Control

Leachate collection system CQC should be

performed by the contractor. Similar activities should be performed for CQA by an

independent party acting on behalf of the

facility manager. The purpose of leachate collection system CQA is to document that the

system is constructed in accordance with

design specifications. 

How can implementation of QA

and QC be ensured for a

leachate collection system?

Prior to construction, CQA staff should

inspect all materials to confirm that they meet

the construction plans and specifications.

These materials include: geonets; geotextiles;

pipes; granular material; mechanical, electrical, and monitoring equipment; concrete

forms and reinforcements; and prefabricated

structures such as sumps and manholes. The

leachate collection system foundation, either a

geomembrane or compacted clay liner, should

also be inspected, upon its completion, to

ensure that it has proper grading and is free

of debris and liquids.

During construction, CQA staff should

observe and document, as appropriate, the

placement and installation of pipes, filter layers, drainage layers, geonets and geotextiles,

sumps, and mechanical and electrical equipment. For pipes, observations might include

descriptions of pipe bedding material, quality

and thickness, as well as the total area covered by the bedding material. Observations

of pipe installations should focus on the location, configuration, and grading of the pipes,

as well as the quality of connections at joints. 

For granular filter layers, CQA activities

might include observing and documenting

material thickness and quality during placement. For granular drainage layers, CQA

might focus on the protection of underlying

liners, material thickness, proper overlap

with filter fabrics and geonets (if applicable),

and documentation of any weather conditions that might affect the overall performance of the drainage layer. For geonets and

7B-34

Protecting Ground Water—Designing and Installing Liners 
other geosynthetics, CQA observations

should focus on the area of coverage and layout pattern, as well as the overlap between

panels. For geonets, CQA staff might want to

make sure that the materials do not become

clogged by granular material that can be carried over, as a result of either wind or runoff

during construction.

Upon completion of construction, each

component should be inspected to identify

any damage that might have occurred during

its installation or during construction of

another component. For example, a leachate

collection pipe can be crushed during placement of a granular drainage layer. Any damage that does occur should be repaired, and

the repairs should be documented in the

CQA records.

Protecting Ground Water—Designing and Installing Liners

7B-35
7B-36

Protecting Ground Water—Designing and Installing Liners 

■ Review the recommended location considerations and operating practices for the unit.

■ Select appropriate liner type—single, composite, or double liner—or in-situ soils, based on risk

characterization.

■ Evaluate liner material properties and select appropriate clay, geosynthetic, or combination of materials; consider interactions of liner and soil material with waste.

■ Develop a construction quality assurance (CQA) plan defining staff roles and responsibilities and

specifying test methods, storage procedures, and construction protocols. 

■ Ensure a stable in-situ soil foundation, for nonengineered liners.

■ Prepare and inspect subgrade for engineered liners.

■ Work with manufacturer to ensure protective shipping, handling, and storage of all materials.

■ Construct a test pad for compacted clay liners.

■ Test compacted clay liner material before and during construction.

■ Preprocess clay material to ensure proper water content, remove oversized particles, and add soil

amendments, as applicable.

■ Use proper lift thickness and number of equipment passes to achieve adequate compaction.

■ Protect clay material from drying and cracking.

■ Develop test strips and trial seams to evaluate geomembrane seaming method.

■ Verify integrity of factory and field seams for geomembrane materials before and during construction.

■ Backfill with soil or geosynthetics to protect geomembranes and geosynthetic clay liners during

construction.

■ Place backfill materials carefully to avoid damaging the underlying materials.

■ Install geosynthetic clay liner with proper overlap.

■ Patch any damage that occurs during geomembrane or geosynthetic clay liner installation.

■ Design leachate collection and removal system to allow adequate flow and to minimize clogging;

include leachate treatment and leak detection systems, as appropriate.

■ Document all CQA activities, including meetings, inspections, and repairs.

Designing and Installing Liners Activity List
Protecting Ground Water—Designing and Installing Liners

7B-37

ASTM D-413. 1993. Standard Test Methods for Rubber Property-Adhesion to Flexible Substrate.

ASTM D-422. 1990. Standard Test Method for Particle-Size Analysis of Soils.

ASTM D-638. 1991. Standard Test Method for Tensile Properties of Plastics.

ASTM D-698. 1991. Test Method for Laboratory Compaction Characteristics of Soil Using Standard

Effort (12,400 ft-lbf/ft3 (600 kN-m/m3

)).

ASTM D-751. 1989. Standard Test Methods for Coated Fabrics.

ASTM D-882. 1991. Standard Test Methods for Tensile Properties of Thin Plastic Sheeting.

ASTM D-1004. 1990. Standard Test Method for Initial Tear Resistance of Plastic Film and Sheeting.

ASTM D-1557. 1991. Test Method for Laboratory Compaction Characteristics of Soil Using Modified

Effort (56,000 ft-lbf/ft3 (2,700 kN-m/m3

)).

ASTM D-4318. 1993. Standard Test Method for Liquid Limit, Plastic Limit, and Plasticity Index of

Soils.

ASTM D-4354. 1989. Standard Practice for Sampling of Geosynthetics for Testing.

ASTM D-4716. 1987. Standard Test Method for Constant Head Hydraulic Transmissivity (In-Plane

Flow) of Geotextiles and Geotextile Related Products.

ASTM D-5084. 1990. Standard Test Method for Measurement of Hydraulic Conductivity of Saturated

Porous Materials Using a Flexible Wall Permeameter.

ASTM D-5199. 1991. Standard Test Method for Measuring Nominal Thickness of Geotextiles and

Geomembranes.

ASTM D-5261. 1992. Standard Test Method for Measuring Mass per Unit Area of Geotextiles.

ASTM D-5321. 1992. Standard Test Method for Determining the Coefficient of Soil and Geosynthetic

or Geosynthetic and Geosynthetic Friction by the Direct Shear Method.

Resources
7B-38

Protecting Ground Water—Designing and Installing Liners 

Resources (cont.)

Bagchi, A. 1994. Design, Construction, and Monitoring of Landfills. 

Berg, R., and L. Well. 1996. A Position Paper on: The Use of Geosynthetic Barriers in Nonhazardous

Industrial Waste Containment.

Berger, E. K. and R. Berger. 1997. The Global Water Cycle.

Borrelli, J. and D. Brosz. 1986. Effects of Soil Salinity on Crop Yields. <hermes.ecn.purdue.edu/cgi/convwqtest?/b-803.wy.ascii>

Boulding, J.R. 1995. Practical Handbook of Soil, Vadose Zone, and Ground Water Contamination:

Assessment, Prevention and Remediation. Lewis Publishers.

Brandt, R.C. and K.S. Martin. 1996. The Food Processing Residual Management Manual. September.

Daniel, D.E., and R.M. Koerner. 1991. Landfill Liners from Top to Bottom. Civil Engineering. December.

Daniel, D.E., and R.M. Koerner. 1993. Technical Guidance Document: Quality Assurance and Quality

Control for Waste Containment Facilities. Prepared for U.S. EPA. EPA600-R-93-182.

Daniel, D.E., and R.M. Koerner. 1995. Waste Containment Facilities: Guidance for Construction, Quality

Assurance and Quality Control of Liner and Cover Systems.

Evanylo, G.K. and W. L. Daniels. 1996. The Value and Suitability of Papermill Sludge and Sludge

Compost as a Soil Amendment and Soilless Media Substitute. Final Report. The Virginia Department of

Agriculture and Consumer Services, P.O. Box 1163, Room 402, Richmond, VA. April.

Federal Test Method Standard 101C. 1980. Puncture Resistance and Elongation Test (1/8 Inch Radius

Probe Method).

Fipps, G. 1995. Managing Irrigation Water Salinity in the Lower Rio Grande Valley. <hermes.ecn.purdue.edu/sgml/water_quality/texas/b1667.ascii>

Geosynthetic Research Institute. 1993. GRI-GCL1, Swell Measurement of the Clay Component of GCLs.

Geosynthetic Research Institute. 1993. GRI-GCL2, Permeability of Geosynthetic Clay Liners (GCLs).
Protecting Ground Water—Designing and Installing Liners

7B-39

Resources (cont.)

Idaho Department of Health and Welfare. 1988. Guidelines for Land Application of Municipal and

Industrial Wastewater. March.

Koerner, R.M. 1994. Designing with Geosynthetics, Third Edition.

McGrath, L., and P. Creamer. 1995. Geosynthetic Clay Liner Applications in Waste Disposal

Facilities.

McGrath, L., and P. Creamer. 1995. Geosynthetic Clay Liner Applications. Waste Age. May.

Michigan Department of Natural Resources, Waste Characterization Unit. 1991. Guidance for Land

Application of Wastewater Sludge in Michigan. March.

Michigan Department of Natural Resources, Waste Characterization Unit. 1991. Guide to Preparing

a Residuals Management Plan. March.

Minnesota Pollution Control Agency. 1993. Land Treatment of Landfill Leachate. February.

Northeast Regional Agricultural Engineering Cooperative Extension. 1996. Nutrient Management

Software: Proceedings from the Nutrient Management Software Workshop. NRAES-100. December.

Northeast Regional Agricultural Engineering Cooperative Extension. 1996. Animal Agriculture and

the Environment: Nutrients, Pathogens, and Community Relations. NRAES-96. December.

Northeast Regional Agricultural Engineering Cooperative Extension. 1993. Utilization of Food

Processing Residuals. Selected Papers Representing University, Industry, and Regulatory

Applications. NRAES-69. March.

North Carolina Cooperative Extension Service. 1994. Soil facts: Careful Soil Sampling - The Key to

Reliable Soil Test Information. AG-439-30.

Oklahoma Department of Environmental Quality. Title 252. Oklahoma Administrative Code,

Chapter 647. Sludge and Land Application of Wastewater.

Sharma, H., and S. Lewis. 1994. Waste Containment Systems, Waste Stabilization, and Landfills:

Design and Evaluation.

Smith, M.E., S. Purdy, and M. Hlinko. 1996. Some Do’s and Don’ts of Construction Quality

Assurance. Geotechnical Fabrics Report. January/February.
7B-40

Protecting Ground Water—Designing and Installing Liners 

Resources (cont.)

Spellman, F. R. 1997. Wastewater Biosolids to Compost.

Texas Water Commission. 1983. Industrial Solid Waste Management Technical Guideline No. 5: Land

Application. December.

Tsinger, L. 1996. Chemical Compatibility Testing: The State of Practice. Geotechnical Fabrics Report.

October/November.

University of Nebraska Cooperative Extension Institute of Agriculture and Natural Resources. 1991.

Guidelines for Soil Sampling. G91-1000-A. February.

U.S. EPA. 2001. Technical Resource Document: Assessment and recommendations for Improving the

Performance of Waste Containment Systems. Draft.

U.S. EPA. 1996a. Issue Paper on Geosynthetic Clay Liners (GCLs). 

U.S. EPA. 1996b. Report of 1995 Workshop on Geosynthetic Clay Liners. EPA600-R-96-149. June.

U.S. EPA. 1995a. A Guide to the Biosolids Risk Assessments for the EPA Part 503 Rule. EPA832-B-93-

005. September.

U.S. EPA. 1995b. Decision Maker’s Guide to Solid Waste Management. Volume II. EPA530-R-95-023.

U.S. EPA. 1995c. Laboratory Methods for Soil and Foliar Analysis in Long-Term Environmental

Monitoring Programs. EPA600-R-95-077.

U.S. EPA. 1995d. Process Design Manual: Land Application of Sewage Sludge and Domestic Septage.

EPA625-R-95-001. September.

U.S. EPA. 1995e. Process Design Manual: Surface Disposal of Sewage Sludge and Domestic Septage.

EPA625-R-95-002. September.

U.S. EPA. 1994a. A Plain English Guide to the EPA Part 503 Biosolids Rule. EPA832-R-93-003.

September.

U.S. EPA. 1994b. Biosolids Recycling: Beneficial Technology for a Better Environment. EPA832-R-94-

009. June.

U.S. EPA. 1994c. Guide to Septage Treatment and Disposal. EPA625-R-94-002. September.
Protecting Ground Water—Designing and Installing Liners

7B-41

Resources (cont.)

U.S. EPA. 1994d. Land Application of Sewage Sludge: A Guide for Land Appliers on the Requirements

of the Federal Standards for the Use or Disposal of Sewage Sludge, 40 CFR Part 503. EPA831-B-93-

002b. December.

U.S. EPA. 1994e. Seminar Publication: Design, Operation, and Closure of Municipal Solid Waste

Landfills. EPA625-R-94-008.

U.S. EPA. 1993a. Domestic Septage Regulatory Guidance: A Guide to the EPA 503 Rule. EPA832-B-92-

005. September.

U.S. EPA. 1993b. Solid Waste Disposal Facility Criteria: Technical Manual. EPA530-R-93-017.

U.S. EPA. 1993c. Technical Guidance Document: Quality Assurance and Quality Control for Waste

Containment Facilities. EPA600-R-93-182.

U.S. EPA. 1992. Control of Pathogens and Vector Attraction in Sewage Sludge. EPA625-R-92-013.

December.

U.S. EPA. 1991a. Seminar Publication: Design and Construction of RCRA/CERCLA Final Covers.

EPA625-4-91-025.

U.S. EPA. 1991b. Seminar Publication: Site Characterization for Subsurface Remediation. EPA625-4-91-

026.

U.S. EPA. 1991c. Technical Guidance Document: Inspection Techniques for the Fabrication of

Geomembrane Field Seams. EPA530-SW-91-051.

U.S. EPA. 1990. State Sludge Management Program Guidance Manual. October.

U.S. EPA. 1989a. Seminar Publication: Requirements for Hazardous Waste Landfill Design,

Construction, and Closure. EPA625-4-89-022.

U.S. EPA. 1989b. Seminar Publication: Corrective Action: Technologies and Applications. EPA625-4-89-

020.

U.S. EPA. 1988. Lining of Waste Containment and Other Impoundment Facilities. EPA600-2-88-052.

U.S. EPA. 1987. Geosynthetic Guidance for Hazardous Waste Landfill Cells and Surface Impoundments.

EPA600-2-87-097.
7B-42

Protecting Ground Water—Designing and Installing Liners 

Resources (cont.)

U.S. EPA. 1986a. Project Summary: Avoiding Failure of Leachate Collection and Cap Drainage Systems.

EPA600-S2-86-058.

U.S. EPA. 1986b. Test Methods for Evaluating Solid Waste: Physical/Chemical Methods. EPASW-846.

U.S. EPA. 1983. Process Design Manual for Land Application of Municipal Sludge. EPA625-1-83-016.

October.

U.S. EPA, U.S. Army Corps of Engineers, U.S. Department of Interior, and U.S. Department of

Agriculture. 1981. Process Design Manual for Land Treatment of Municipal Wastewater. EPA625-1-81-

013. October.

U.S. EPA. 1979. Methods for Chemical Analysis of Water and Wastes. EPA600-4-79-020.

Viessman Jr., W. and M.J. Hammer. 1985. Water Supply and Pollution Control. 4th ed.

Washington State Department of Ecology. 1993. Guidelines for Preparation of Engineering Reports for

Industrial Wastewater Land Application Systems. Publication #93-36. May.

Webber, M.D. and S.S. Sing. 1995. Contamination of Agricultural Soils. In Action, D.F. and L.J.

Gregorich, eds. The Health of Our Soils.

Wisconsin Department of Natural Resources. 1996. Chapter NR 518: Landspreading of Solid Waste. April.
Protecting Ground Water—Designing and Installing Liners

7B-43

Geosynthetic Materials25

Geotextiles

Geotextiles form one of the two largest

group of geosynthetics. Their rise in growth

during the past fifteen years has been nothing

short of awesome. They are indeed textiles in

the traditional sense, but consist of synthetic

fibers rather than natural ones such as cotton,

wool, or silk. Thus biodegradation is not a

problem. These synthetic fibers are made into

a flexible, porous fabric by standard weaving

machinery or are matted together in a random, or nonwoven, manner. Some are also

knit. The major point is that they are porous

to water flow across their manufactured plane

and also within their plane, but to a widely

varying degree. There are at least 80 specific

application areas for geotextiles that have been

developed; however, the fabric always performs at least one of five discrete functions:

1. Separation

2. Reinforcement

3. Filtration

4. Drainage

5. Moisture barrier (when impregnated)

Geogrids

Geogrids represent a rapidly growing segment within the geosynthetics area. Rather

than being a woven, nonwoven or knit textile

(or even a textile-like) fabric, geogrids are

plastics formed into a very open, gridlike

configuration (i.e., they have large apertures).

Geogrids are either stretched in one or two

directions for improved physical properties or

made on weaving machinery by unique

methods. By themselves, there are at least 25

application areas, however, they function

almost exclusively as reinforcement materials.

Geonets

Geonets, called geospacers by some, constitute another specialized segment within the

geosynthetic area. They are usually formed by

a continuous extrusion of parallel sets of

polymeric ribs at acute angles to one another.

When the ribs are opened, relatively large

apertures are formed into a netlike configuration. Their design function is completely

within the drainage area where they have

been used to convey fluids of all types.

Geomembranes

Geomembranes represent the other largest

group of geosynthetics and in dollar volume

their sales are probably larger than that of

geotextiles. Their growth has been stimulated

by governmental regulations originally enacted in 1982. The materials themselves are

“impervious” thin sheets of rubber or plastic

material used primarily for linings and covers

of liquid- or solid-storage facilities. Thus the

primary function is always as a liquid or

vapor barrier. The range of applications, however, is very great, and at least 30 individual

applications in civil engineering have been

developed.

Geosynthetic Clay Liners

Geosynthetic clay liners (or GCLs) are the

newest subset within geosynthetic materials.

They are rolls of factory fabricated thin layers

of bentonite clay sandwiched between two

geotextiles or bonded to a geomembrane.

Structural integrity is maintained by needle

punching, stitching or physical bonding.

They are seeing use as a composite compo25 Created by Geosynthetic Research Institute. Accessed from the Internet on October 16, 2001 at

<www.drexel.edu/gri/gmat.html>.

Appendix
7B-44

Protecting Ground Water—Designing and Installing Liners 

nent beneath a geomembrane or by themselves as primary or secondary liners.

Geopipe (aka Buried Plastic Pipe)

Perhaps the original geosynthetic material

still available today is buried plastic pipe. This

“orphan” of the Civil Engineering curriculum

was included due to an awareness that plastic

pipe is being used in all aspects of geotechnical, transportation, and environmental engineering with little design and testing

awareness. This is felt to be due to a general

lack of formalized training. The critical nature

of leachate collection pipes coupled with high

compressive loads makes geopipe a bona-fide

member of the geosynthetics family. The function is clearly drainage.

Geocomposites

A geocomposite consists of a combination

of geotextile and geogrid; or geogrid and

geomembrane; or geotextile, geogrid, and

geomembrane; or any one of these three

materials with another material (e.g.,

deformed plastic sheets, steel cables, or steel

anchors). This exciting area brings out the

best creative efforts of the engineer, manufacturer, and contractor. The application areas

are numerous and growing steadily. The

major functions encompass the entire range

of functions listed for geosynthetics discussed

previously: separation, reinforcement, filtration, drainage, and liquid barrier.

“Geo-Others”

The general area of geosynthetics has

exhibited such innovation that many systems

defy categorization. For want of a better

phrase, geo-others, describes items such as

threaded soil masses, polymeric anchors, and

encapsulated soil cells. As with geocomposites their primary function is product-dependent and can be any of the five major

functions of geosynthetics.