United States
Environmental Protection
Agency
Solid Waste
and Emergency Response
(5306W)
EPA530-F-97-002
Revised December 2001
Geosynthetic Clay Liners
Used in Municipal
Solid Waste Landfills
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 per-
formance 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 cost-
effective 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 con-
struct 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.
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 perfor-
mance characteristics, the primary performance
factors are clay quality, amount of clay used per
unit area, and uniformity.
Bentonite is an extremely absorbent, granu-
lar clay formed from volcanic ash. Bentonite
attracts positively charged water particles;
thus, it rapidly hydrates when exposed to liq-
uid, such as water or leachate. As the clay
hydrates it swells, giving it the ability to "self-
heal" 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 proper-
ties that make it an effective barrier system.
) Printed on paper that contains at least 20 percent postconsumer fiber.
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Figure 1. General Configurations of GCLs
Bentonite Sandwiched Between Two Geotextiles
Geotextile
Bentonite
Geotextile
Bentonite Glued to Geomembrane
Bentonite
Geomembrane-
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 con-
sideration to ensure that its hydraulic
conductivity, as well as other character-
istics, are appropriate for the particular
landfill site.
Hydraulic Conductivity
GCL technology can provide barrier
systems with low hydraulic conductivi-
ty (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, how-
ever, the hydraulic conductivity of ben-
tonite 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 com-
pound 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 ben-
tonite 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 1O!
cm/sec to less than 1 x 1042 cm/sec.
That is, the permeability of finished
GCL products depends on a combina-
tion 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 configura-
tion of the barrier system, GCL tech-
nology 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 bar-
rier. In addition, needlepunching
requires the use of a nonwoven geotex-
tile on at least one side. These GCL
configurations provide enhanced inter-
face friction resistance to the adjoining
layer, an important consideration for
landfill slopes.
Both needlepunching and stitch-
bonding, however, tend to increase the
cost of the GCL product. Needle-
punching, in particular, adds to a
GCL's cost, because nonwoven geotex-
tiles are generally more expensive than
woven geotextiles.
Before selecting a final barrier sys-
tem, landfill operators should consider
other important performance charac-
teristics, such as free and confined
swelling (i.e., whether the clay will pro-
vide a uniform barrier) and rate of
creep, which measures the resistance to
barrier deformation.
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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 labora-
tory tests for assessing mass per unit
area (ASTM D-3776), hydraulic con-
ductivity (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 perme-
ability. 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 over-
burden stress around the GCL during
testing. The higher the effective overbur-
den stress, the lower the hydraulic con-
ductivity. When comparing two different
bentonite products, both must be sub-
jected to the same degree of effective
overburden stress.
Available GCL
Products
Product Types
The following types of GCL products
are currently available:
Geotextile type:
Bentofixฎ (activated sodium
bentonite as primary ingredient
and affixed by needlepunching
to a woven or nonwoven upper
geotextile and a nonwoven lower
geotextile).
Bentomatฎ (sodium bentonite
as primary ingredient and affix-
ed by needlepunching to a
Figure 2. Affixing Bentonite to Geotextiles
Clay Bound With Adhesive to
Upper and Lower Geotextiles
'5mm
$ฃฃ#
CLAY AND ADHESIVE
Hi
Upper Geotextile
Lower Geotextile
Clay Stitchbonded Between
Upper and Lower Geotextiles
'5mm
1
CLAY AND ADHESIVE OR CLAY
vvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvvv
VAAA .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .. .-\ A. A
'
Upper Geotextile
. Stitchbonded in
Rows
Lower Geotextile
Clay Needlepunched Through
Upper and Lower Geotextiles
f V V V V V V V V V V V V V V V V V V V V V V V V V V
\ A. A. A .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--. .--\ A. A. A
> >
-Upper Geotextile
Needlepunched
- Fibers
Throughout
Lower Geotextile
woven or nonwoven upper geo-
textile and a nonwoven lower
geotextile).
Claymaxฎ (sodium bentonite as
primary ingredient mixed with
water-soluble adhesive and bond-
ed or Stitchbonded to a woven
upper and lower geotextile).
Geomembrane type:
Gundsealฎ (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 varia-
tions of these product types by manu-
facturer, 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.
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Table 1. Principal GCL Products Available in the United States
Manufacturer &
Product Name
Upper
Geosynthetica
Lower
Geosynthetica
Bonding Method
Standard Roll
Width x Length
(feet)
Fluid Systems, Inc. (FSI) (Germany)
Bentofix NS
Bentofix WP
Bentofix NW
woven
woven
b
nonwoven
nonwoven
nonwoven
nonwoven
needlepunched
needlepunched
needlepunched
(15.2x100)
(15.2x100)
(15.2x100)
Colloid Environmental Technologies Company (CETCO) (United States)
Claymax 200R
Claymax 500SP
Claymax 506SP
Bentomat "ST"
Bentomat "N"
woven
woven
woven
woven
nonwoven
woven
woven
woven
nonwoven
nonwoven
adhered
adhered and stitchbonded
adhered and stitchbonded
needlepunched
needlepunched
(13.83x150)
(13.83x150)
(13.83x150)
(15.3x125)
(15.3x125)
GSE Environmental (United States)0
Gundseal HD 20
Gundseal HD 30
Gundseal HD 30
Gundseal HD 60
Gundseal HD 80
Gundseal HD 40
Gundseal HD 60
Gundseal HD 80
d
none
d
none
d
none
d
none
d
none
d
none
d
none
d
none
HDPEe
HOPE
HDPE/VLDPEf
HDPE/VLDPE
HDPE/VLDPE
textured HOPE
textured HOPE
textured HOPE
adhered
adhered
adhered
adhered
adhered
adhered
adhered
adhered
(17.5x200)
(17.5x200)
(17.5x200)
(17.5x170)
(17.5x150)
(17.5x200)
(17.5x200)
(17.5x200)
a These properties vary by product and application.
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.
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.
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Installation
Landfill operators can install all available
GCL products much faster and more easily
than compacted clay liners. Unlike com-
pacted 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 indi-
vidual 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 con-
siderations vary with the particular
GCL product. Thus, installers should
follow the manufacturer's instructions
for the particular product.
GCL manufacturers, and some pri-
vate engineering firms, provide training
for GCL installers. Among other con-
siderations, 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 inspec-
tion of GCL installations.
Figure 3. Available GCL Products
Bentofix and Bentomat
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H-H-H-H-H-H-
SODIUM BENTONITE
-Woven Geotextile
Needlepunched
Fibers
Nonwoven
Geotextile
Claymax 200R
\-\'\'\'\-
SODIUM BENTONITE
MIXED WITH AN ADHESIVE
Woven Geotextile
.Op en-Weave
Geotextile
Claymax 500SP
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SODIUM BENTONITE
MIXED WITH AN ADHESIVE
i-H-H-H-H-H
\'\'\'\'\-
-Woven Geotextile
Sewn Stitches
Woven Geotextile
Gundseal
KSftfr
SODIUM BENTONITE
MIXED WITH AN ADHESIVE
ฃSS&
Polyethylene
Geomembrane
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.
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Issues To Be
Addressed
This emerging technology requires addi-
tional 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 con-
ductivity of various GCL configura-
tions 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' recommen-
dations), 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 stabili-
ty of GCLs used in landfill sidewall
applications to determine whether this
use of GCLs provides sufficient resis-
tance to internal shear and physical dis-
placement. 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 prod-
ucts (see Figure 3) are subjected to dur-
ing 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 1O11 cm/sec was unaltered after
five freeze and thaw cycles. Full-scale
field tests still must be conducted, how-
ever, 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 val-
ues, must be established. Additional
testing procedures must be developed,
and all methods should be standard-
ized to facilitate the realistic compari-
son of different GCL products.
Construction and Installation
Procedures
Standardized practices must be devel-
oped 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.
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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 geograph-
ic 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 geomem-
brane 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)
Geo textile
Polyvinyl chloride geomembrane (30-mil thickness)
Claymax
Geo textile
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,
not constitute or imply endorsement or
approval for use by the U.S.
Environmental Protection Agency.
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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, WE., 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, WR. 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
United States
Environmental Protection Agency
(5306W)
Washington, DC 20460
Official Business
Penalty for Private Use
$300
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