1EPA

United States 

Environmental Protection 

Agency

EPA530-F-97-002

Revised December 2001

Solid Waste

and Emergency Response

(5306W)

Geosynthetic Clay Liners 

Used in Municipal 

Solid Waste Landfills

GCL Technology

Materials

A GCL is a relatively thin layer of processed

clay (typically bentonite) either bonded to a

geomembrane or fixed between two sheets of

geotextile. A geomembrane is a polymeric sheet

material that is impervious to liquid as long as

it maintains its integrity. A geotextile is a woven

or nonwoven sheet material less impervious to

liquid than a geomembrane, but more resistant

to penetration damage. Both types of GCLs are

illustrated in Figure 1. Although the overall

configuration of the GCL affects its performance characteristics, the primary performance

factors are clay quality, amount of clay used per

unit area, and uniformity. 

Bentonite is an extremely absorbent, granular clay formed from volcanic ash. Bentonite

attracts positively charged water particles;

thus, it rapidly hydrates when exposed to liquid, such as water or leachate. As the clay

hydrates it swells, giving it the ability to “selfheal” holes in the GCL. In laboratory tests on

bentonite, researchers demonstrated that a

hole up to 75 millimeters in diameter will seal

itself, allowing the GCL to retain the properties that make it an effective barrier system.

T his fact sheet describes new and innovative technologies and products that meet

the performance standards of the Criteria for Municipal Solid Waste Landfills (40

CFR Part 258).

Geosynthetic clay liners (GCLs) represent a relatively new technology (developed in

1986) currently gaining acceptance as a barrier system in municipal solid waste landfill

applications. Federal and some state regulations specify design standards for bottom liners

and final covers. Alternative technologies are allowed, however, if they meet federal performance standards. GCL technology is an alternative that performs at or above standard

federal performance levels. 

GCL technology offers some unique advantages over conventional bottom liners and

covers. GCLs, for example, are fast and easy to install, have low hydraulic conductivity

(i.e., low permeability), and have the ability to self-repair any rips or holes caused by

the swelling properties of the bentonite from which they are made. GCLs are costeffective in regions where clay is not readily available. A GCL liner system is not as

thick as a liner system involving the use of compacted clay, enabling engineers to construct landfills that maximize capacity while protecting area ground water.

The following ASTM standards have been developed which may be used for designing

liner systems using GCLs as well as comparing GCL products:

• ASTM D5889 Standard Practice For Quality Control of GCLs. 

• ASTM D5887 Standard Test Method for Measurement of Index Flux through Saturated

GCL Specimens Using a Flexible Wall Permeatameter.

• ASTM D5890 Standard Test Method for Swell Index of Clay Mineral Component of GCLs.

• ASTM D5891 Standard Test Method for Fluid Loss of Clay Liner Component of GCLs.

• ASTM D5993 Standard Test Method for Measuring Mass per Unit of GCLs.

• ASTM D6243 Standard Test Method for Determining the Internal and Interface Shear

Resistance of GCL by Direct Shear Method.

This emerging technology is currently in use at a number of sites across the

nation. This fact sheet provides information on this technology and presents case

studies of successful applications. 

2Printed on paper that contains at least 20 percent postconsumer fiber.
Bentonite is affixed to synthetic

materials in a number of ways to form

the GCL system. In configurations

using a geomembrane, the clay is

affixed using an adhesive. In geotextile

configurations, however, adhesives,

stitchbonding, needlepunching, or a

combination of the three, are used.

Although stitchbonding and

needlepunching create small holes in

the geotextile, these holes are sealed

when the installed GCL’s clay layer

hydrates. Figure 2 shows cross-section

views of the three separate approaches

to affixing bentonite to a geotextile.

Properties and

Characteristics

An important criterion for selecting an

effective landfill barrier system is

hydraulic conductivity. Before choosing

a barrier system, the landfill operator

should test the technology under consideration to ensure that its hydraulic

conductivity, as well as other characteristics, are appropriate for the particular

landfill site.

Hydraulic Conductivity

GCL technology can provide barrier

systems with low hydraulic conductivity (i.e., low permeability), which is the

rate at which a liquid passes through a

material. Laboratory tests demonstrate

that the hydraulic conductivity of dry,

unconfined bentonite is approximately

1 x 10-6 cm/sec. When saturated, however, the hydraulic conductivity of bentonite typically drops to less than 

1 x 10-9 cm/sec.

The quality of the clay used affects a

GCL’s hydraulic characteristics. Sodium

bentonite, a naturally occurring compound in a silicate clay formed from

volcanic ash, gives bentonite its distinct

properties. Additives are used to

enhance the hydraulic properties of

clay containing low amounts of sodium

bentonite.

Hydraulic performance also relates

to the amount of bentonite per unit

area and its uniformity. The more bentonite used per unit area, the lower the

system’s hydraulic conductivity.

Although the amount of bentonite per

unit area varies with the particular

GCL, manufacturers typically use 1

pound per square foot. As a result, the

hydraulic conductivity of most GCL

products ranges from about 1 x 10-5

cm/sec to less than 1 x 10-12 cm/sec.

That is, the permeability of finished

GCL products depends on a combination of factors, including the type and

amount of bentonite, the amount of

additives, the type of geosynthetic

material, and the product configuration

(i.e., the method of affixing the

geosynthetic to the clay).

Shear Strength and Other

Characteristics

Depending on the particular configuration of the barrier system, GCL technology can provide considerable shear

strength (i.e., the maximum stress a

material can withstand without losing

structural integrity). In particular, a

geotextile-backed GCL, with bentonite

affixed via stitchbonding, provides

additional internal resistance to shear

in the clay layer. Needlepunching

yields an even stronger, more rigid barrier. In addition, needlepunching

requires the use of a nonwoven geotextile on at least one side. These GCL

configurations provide enhanced interface friction resistance to the adjoining

layer, an important consideration for

landfill slopes.

Both needlepunching and stitchbonding, however, tend to increase the

cost of the GCL product. Needlepunching, in particular, adds to a

GCL’s cost, because nonwoven geotextiles are generally more expensive than

woven geotextiles.

Before selecting a final barrier system, landfill operators should consider

other important performance characteristics, such as free and confined

swelling (i.e., whether the clay will provide a uniform barrier) and rate of

creep, which measures the resistance to

barrier deformation.

Figure 1. General Configurations of GCLs

Bentonite Sandwiched Between Two Geotextiles

Bentonite Glued to Geomembrane

Geotextile

Bentonite

Geomembrane

Bentonite

Geotextile

2
Testing

GCL configurations for barrier systems

are based on the design specifications

of each specific project. The American

Society for Testing and Materials

(ASTM) developed standardized laboratory tests for assessing mass per unit

area (ASTM D-3776), hydraulic conductivity (ASTM D-5084), and direct

shear (ASTM D-5321).

Researchers at the Geosynthetic

Research Institute at Drexel University

(in Philadelphia, Pennsylvania) and the

Geotechnical Engineering Department

at the University of Texas (in Austin)

developed tests to measure shear

strength, as well as confined swelling,

rate of creep, and seam overlap permeability. These test methods have been

adopted by ASTM. Additionally, the

bentonite industry developed a test to

measure free swell (USP-NF-XVII).

Test values for hydraulic conductivity

depend on the degree of effective overburden stress around the GCL during

testing. The higher the effective overburden stress, the lower the hydraulic conductivity. When comparing two different

bentonite products, both must be subjected to the same degree of effective

overburden stress.

Available GCL

Products

Product Types

The following types of GCL products

are currently available: 

 Geotextile type:

— Bentofix® (activated sodium

bentonite as primary ingredient

and affixed by needlepunching

to a woven or nonwoven upper

geotextile and a nonwoven lower

geotextile).

— Bentomat® (sodium bentonite

as primary ingredient and affixed by needlepunching to a

woven or nonwoven upper geotextile and a nonwoven lower

geotextile).

— Claymax® (sodium bentonite as

primary ingredient mixed with

water-soluble adhesive and bonded or stitchbonded to a woven

upper and lower geotextile).

 Geomembrane type:

— Gundseal® (sodium bentonite as

the primary ingredient mixed with

an adhesive and bonded to a blend

of high density polyethylene and

very low density polyethylene).

Table 1 lists information on variations of these product types by manufacturer, and Figure 3 presents

cross-section views of these product

configurations.

In general, manufacturers ship GCL

products in rolled sheets ranging from

13 to 18 feet wide and from 100 to 200

feet long. GCLs range in thickness from

0.2 to 0.3 inches.

Clay Needlepunched Through 

Upper and Lower Geotextiles

Clay Stitchbonded Between 

Upper and Lower Geotextiles

Clay Bound With Adhesive to 

Upper and Lower Geotextiles

Upper Geotextile

Upper Geotextile

Upper Geotextile

Lower Geotextile

Lower Geotextile

Lower Geotextile

Stitchbonded in

Rows

Needlepunched

Fibers

Throughout

~5mm

~5mm

~4-6mm CLAY

CLAY AND ADHESIVE OR CLAY

CLAY AND ADHESIVE

Figure 2. Affixing Bentonite to Geotextiles

3
Bentofix NS woven nonwoven needlepunched (15.2 x 100)

Bentofix WP woven nonwoven needlepunched (15.2 x 100)

Bentofix NW nonwovenbnonwoven needlepunched (15.2 x 100)

Claymax 200R woven woven adhered (13.83 x 150)

Claymax 500SP woven woven adhered and stitchbonded (13.83 x 150)

Claymax 506SP woven woven adhered and stitchbonded (13.83 x 150)

Bentomat “ST” woven nonwoven needlepunched (15.3 x 125)

Bentomat “N” nonwoven nonwoven needlepunched (15.3 x 125)

Gundseal HD 20 nonedHDPEeadhered (17.5 x 200)

Gundseal HD 30 nonedHDPE adhered (17.5 x 200)

Gundseal HD 30 nonedHDPE/VLDPEfadhered (17.5 x 200)

Gundseal HD 60 nonedHDPE/VLDPE adhered (17.5 x 170)

Gundseal HD 80 nonedHDPE/VLDPE adhered (17.5 x 150)

Gundseal HD 40 nonedtextured HDPE adhered (17.5 x 200)

Gundseal HD 60 nonedtextured HDPE adhered (17.5 x 200)

Gundseal HD 80 nonedtextured HDPE adhered (17.5 x 200)

Manufacturer & Upper Lower Bonding Method Standard Roll

Product Name Geosynthetica Geosynthetica Width x Length 

(feet)

Table 1. Principal GCL Products Available in the United States

a These properties vary by product and application.

b Nonwoven layer is scrim (a woven, open-mesh reinforcing fabric made from continuous-filament yarn) reinforced.

c All Gundseal products can be manufactured in 8-foot widths and with leachate-resistant bentonite. Products with

backings that are 40 mils or greater can be manufactured with VLDPE as the lower geosynthetic material.

d Can be manufactured with a nonwoven, 0.75-ounce-per-square-yard geotextile as the upper geosynthetic material.

e High density polyethylene.

f Very low density polyethylene.

GSE Environmental (United States)c

Colloid Environmental Technologies Company (CETCO) (United States)

Fluid Systems, Inc. (FSI) (Germany)

4
Installation

Landfill operators can install all available

GCL products much faster and more easily

than compacted clay liners. Unlike compacted clay liners, however, GCLs are

more susceptible to damage during

transport and installation. Care should

be taken during and after installation to

avoid hydration. Hydration results in

unconfined swelling of the bentonite

and causes the geotextile layers to pull

apart, undermining the integrity of the

GCL configuration. 

Manufacturers usually specify individual GCL installation procedures.

Basic procedures, however, call for

rolling out the large GCL sheets onto

the site subgrade, which should be

smooth (e.g., free of stones and grade

stakes), well compacted, and dry. Once

installers cover the GCL with soil, the

GCL hydrates by drawing moisture

from the soil. As a result, when laying

out the GCL, installers must allow

enough seam overlap at adjoining

sheets to guard against the potential

opening of the barrier system.

Currently, the recommended amount

of seam overlap and other seaming considerations vary with the particular

GCL product. Thus, installers should

follow the manufacturer’s instructions

for the particular product. 

GCL manufacturers, and some private engineering firms, provide training

for GCL installers. Among other considerations, instructions typically

emphasize techniques for minimizing

potential damage to the GCL during

installation. The National Institute for

Certification of Engineering

Technologists in Alexandria, Virginia,

offers a certification program in quality

assurance and quality control inspection of GCL installations.

Costs

As of 1994, the cost of an installed GCL

ranged from $0.42 to $0.60 per square

foot. Factors affecting the cost of a GCL

include:

 Shipping distance

 Size of the job

 Market demand 

 Time of the year

In general, GCL barrier systems are

especially cost-effective in areas where

clay is not readily available for use 

as a liner material.

Figure 3. Available GCL Products

Bentofix and Bentomat

Woven Geotextile

Woven Geotextile

Woven Geotextile

Woven Geotextile

Polyethylene

Geomembrane

Sewn Stitches

Open-Weave

Geotextile

Nonwoven 

Geotextile

Needlepunched

Fibers

Claymax 200R

Claymax 500SP

Gundseal

SODIUM BENTONITE

SODIUM BENTONITE

MIXED WITH AN ADHESIVE

SODIUM BENTONITE

MIXED WITH AN ADHESIVE

SODIUM BENTONITE

MIXED WITH AN ADHESIVE

5
Issues To Be

Addressed

This emerging technology requires additional field and laboratory testing to

further assess its effectiveness as a

landfill barrier system in terms of the

key performance factors discussed

below. Improved product design and

installation standards must also be

established.

Performance Factors

Further research is needed into the

following key performance factors of

GCLs:

Hydraulic Conductivity

Available data on the hydraulic conductivity of various GCL configurations are gathered exclusively under

laboratory conditions. Data from

field tests should be collected to

establish product design values.

Bearing Capacity

A study by the Geosynthetic

Research Institute provides the basis

for allaying some concerns about the

bearing capacity of hydrated GCLs,

but more research is needed. The

study demonstrated that an adequate

layer of cover soil (according to the

product manufacturers’ recommendations), placed on GCLs during

installation, prevents a decrease in

liner thickness with the application

of a load. Without a sufficient soil

layer, GCLs become compressed, 

raising their hydraulic conductivity

(i.e., making them more permeable)

and reducing their effectiveness as a

barrier.

Slope Stability 

Research is ongoing on the slope stability of GCLs used in landfill sidewall

applications to determine whether this

use of GCLs provides sufficient resistance to internal shear and physical displacement. Additional data are needed

to support the preliminary results of a

U.S. Environmental Protection Agency

field study indicating good stability of

GCL technology following capping

operations. This study mimicked the

construction stresses all four GCL products (see Figure 3) are subjected to during capping. Constructed in November

1994, the study site used five plots of

GCL placed at a 3 to 1 slope and eight

plots placed at a 2 to 1 slope. All plots

had a 3-foot-thick soil cap. Researchers

collected information on the soil and

clay moisture of the GCL using internal

probes, and they measured the GCL for

physical displacement. Results to date

indicate good slope stability for all plots.

Long-Term Reliability

The geotextile or geomembrane in

GCL products remains durable for

long periods of time.

Freeze and Thaw Cycles

Freeze and thaw cycles do not affect

GCLs used in landfill bottom liner

applications because these systems are

installed below the frost line. Limited

laboratory data indicate that the

hydraulic conductivity of GCLs is not

affected by freeze and thaw cycles.

Laboratory tests performed on a 

bentonitic blanket indicate that

hydraulic conductivity before freezing

of 2 x 10-11 cm/sec was unaltered after

five freeze and thaw cycles. Full-scale

field tests still must be conducted, however, to corroborate the laboratory data,

especially for GCL technology used as

an infiltration barrier in landfill caps.

Design and Installation

Standards

The following issues must be

addressed to encourage the further

development of GCL technology as a

landfill barrier system:

Material Properties and Additional

Testing Methods

To allow design engineers to develop

more precise site specifications, a list

of important performance properties

for materials used in GCL products,

as well as minimum performance values, must be established. Additional

testing procedures must be developed,

and all methods should be standardized to facilitate the realistic comparison of different GCL products.

Construction and Installation 

Procedures

Standardized practices must be developed to address GCLs’ vulnerability to

the following:

 System stress from inclement weather

after installation.

 Potential for lack of hydration of

bentonite clay in arid regions.

 Punctures in the barrier system

(reducing the barrier potential of

both the clay and the geosynthetics).

 System decay caused by biological

intruders, such as burrowing animals

and tree roots (potentially affecting

both the clay and the geosynthetics).

Additionally, a standardized quality

assurance and quality control program

must be developed.

6
Case Studies

The following case studies illustrate some of the

uses of GCL technology as a barrier system in

landfills. Currently available information from

these sites relates to installation only; long-term

performance is still being assessed. Only one of

the studies concerns the use of GCL technology

in bottom liner applications, because this use is

relatively new. The other two studies focus on cap

system applications, which represent a slightly

more established use of the technology. The case

studies represent sites in three different geographic regions and involve three different GCL 

products.

GCL Landfill Liner: 

Broad Acre Landfill

Pueblo, Colorado

Broad Acre Landfill installed a liner system in 1991

that included:

 A 60-mil Gundseal GCL

 1 foot of compacted clay

According to landfill operators, the Gundseal

was easy to work with. They installed 200,000

square feet in 1 week. Workers installed the liner

with the bentonite side down (i.e., the geomembrane side up). As of February 1996, landfill

officials reported that the liner was functioning

effectively. No releases of leachate have been

detected by the ground-water monitoring 

system.

GCL Landfill Cap: 

Whyco Chromium Landfill

Thomaston, Connecticut

During July 1989, Whyco Chromium Landfill

installed a Claymax 200R GCL in a cap system that

included the following (from top to bottom):

 6 inches of topsoil

 24 inches of earthen material

 Geogrid (for tensile strength)

 Geotextile

 Polyvinyl chloride geomembrane (30-mil thickness)

 Claymax

 Geotextile

The landfill site occupies 41,000 square feet, and

workers installed the Claymax product in 1 day.

Thus far, the cap is functioning well.

GCL Landfill Cap: 

Enoree Landfill

Greenville, South Carolina

In August 1994, the first phase of closure at the

Enoree Landfill involved installing the following

cap system:

 6 to 12 inches of new and native soil

 18 inches of compacted clay

 Bentofix GCL

Enoree staff capped approximately 26 acres of the

landfill in 6 weeks. Landfill officials report that the

cap is functioning effectively.

The mention of publications, products,

or organizations in this fact sheet does

not constitute or imply endorsement or

approval for use by the U.S.

Environmental Protection Agency.

7
References

Daniel, D.E., and R.B. Gilbert. 1994. Geosynthetic Clay Liners for Waste

Containment and Pollution Prevention. Austin, Texas: University of Texas at

Austin. February.

Koerner, R.M., and D. Narejo. 1995. Bearing capacity of hydrated 

geosynthetic clay liners. J. Geotech. Eng., January:82-85.

Shan, H.Y., and D.E. Daniel. 1991. Results of Laboratory Tests on a

Geotextile/Bentonite Liner Material. Proceedings, Geosynthetics 1991,

Industrial Fabrics Association International, St. Paul, MN, vol. 2, 

pp. 517-535.

U.S. EPA. 1995. Effect of Freeze/Thaw on the Hydraulic Conductivity of

Barrier Materials: Laboratory and Field Evaluation. EPA600-R-95-118.

Prepared by Kraus, J.F., and C.H. Benson for the Risk Reduction Engineering

Laboratory, Cincinnati, OH.

Sources of Additional

Information 

ASTM. 1994. ASTM Standards and Other Specifications and Test Methods

on the Quality Assurance of Landfill Liner Systems. ASTM, 1916 Race Street,

Philadelphia, PA. April.

Daniel, D.E. 1992. Compacted Clay and Geosynthetic Clay Liners. American

Society of Civil Engineers National Chapter Section: Geotechnical Aspects of

Landfill Design. National Academy of Sciences, Washington, DC. January.

Daniel, D.E., and R.M. Koerner. 1993. Geotechnical Aspects of Waste

Disposal (ch. 18). In: Daniel, D.E., ed., Geotechnical Practice for Waste

Disposal. Chapman and Hall, London.

Elth, A.W., J. Boschuk, and R.M. Koerner. Prefabricated Bentonite Clay

Layers. Geosynthetic Research Institute, Philadelphia, PA.

Estornell, P. 1991. Bench-Scale Hydraulic Conductivity Tests of Bentonitic

Blanket Materials for Liner and Cover Systems. University of Texas at Austin.

August.

Fang, H.Y. 1995. Bacteria and Tree Root Attack on Landfill Liners: Waste

Disposal by Landfill. Balkema, Rotterdam, pp. 419-426.

Fang, H.Y., S. Pamukcu, and R.C. Chaney. 1992. Soil-Pollution Effects on

Geotextile Composite Walls. American Society for Testing and Materials.

Special Technical Publication 1129:103-116.

Grube, W.E., and D.E. Daniel. 1991. Alternative Barrier Technology for

Landfill Liner and Cover Systems. Air and Waste Management Association,

84th Annual Meeting and Exhibition, Vancouver, British Columbia,

June 16-21.

Koerner, R.M. 1994. Designing with Geosynthetics. Third ed. Prentice Hall.

McGrath, L.T., and P.D. Creamer. 1995. Geosynthetic clay liner application.

Waste Age Magazine, May:99-104.

Schubert, W.R. 1987. Bentonite Matting in Composite Lining Systems.

Geotechnical Practice for Waste Disposal. American Society of Civil

Engineers, New York, NY, pp. 784-796.

U.S. EPA. 1990. Compilation of Information on Alternative Barriers for Liner

and Cover Systems. EPA600-R-91-002. Prepared by Daniel, D.E., and P.M.

Estornell for Office of Research and Development, Washington, DC. October.

U.S. EPA. 1992. Construction Quality Management for Remedial Action and

Remedial Design Waste Containment Systems. Technical Guidance

Document. EPA540-R-92-073. Risk Reduction Engineering Laboratory,

Cincinnati, OH.

U.S. EPA. 1993. Report of Workshop on Geosynthetic Clay Liners. EPA600-

R-93-171. Office of Research and Development, Washington, DC. August.

U.S. EPA. 1993. Quality Assurance and Quality Control for Waste

Containment Facilities. Technical Guidance Document. EPA600-R-93-182.

Risk Reduction Engineering Laboratory, Cincinnati, OH. September.

U.S. EPA. 1996. Report of 1995 Workshop on Geosynthetic Clay Liners.

EPA600-R-96-149. Washington, DC. June

1EPA

United States 

Environmental Protection Agency

(5306W)

Washington, DC 20460

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