# 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 clayhydrates 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 sealitself, 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 linersand 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 bythe 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 asthick 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.



# 2 Printed 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 operatorshould test the technology under consideration to ensure that its hydraulicconductivity, as well as other characteristics, are appropriate for the particular landfill site. Hydraulic Conductivity

GCL technology can provide barriersystems 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. Sodiumbentonite, 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 unitarea 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 finishedGCL 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 CharacteristicsDepending 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. Needlepunchingyields an even stronger, more rigid barrier. In addition, needlepunchingrequires the use of a nonwoven geotextile on at least one side. These GCLconfigurations 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 aGCL’s cost, because nonwoven geotextiles are generally more expensive than woven geotextiles.Before selecting a final barrier system, landfill operators should considerother important performance characteristics, such as free and confinedswelling (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

2Testing

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 conductivitydepend on the degree of effective overburden stress around the GCL duringtesting. The higher the effective overburden stress, the lower the hydraulic conductivity. When comparing two differentbentonite 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 bentoniteas 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 withwater-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 

# ~ 5 mm



# ~ 5 mm



# ~ 4-6mm CLAY CLAY AND ADHESIVE OR CLAY CLAY AND ADHESIVE Figure 2. Affixing Bentonite to Geotextiles

3Bentofix NS woven nonwoven needlepunched (15.2 x 100)
Bentofix WP woven nonwoven needlepunched (15.2 x 100)

Bentofix NW nonwovenb nonwoven 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 none d HDPEe adhered (17.5 x 200)

Gundseal HD 30 none d HDPE adhered (17.5 x 200)

Gundseal HD 30 none d HDPE/VLDPEf adhered (17.5 x 200)

Gundseal HD 60 none d HDPE/VLDPE adhered (17.5 x 170)

Gundseal HD 80 none d HDPE/VLDPE adhered (17.5 x 150)

Gundseal HD 40 none d textured HDPE adhered (17.5 x 200)

Gundseal HD 60 none d textured HDPE adhered (17.5 x 200)

Gundseal HD 80 none d textured 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 )

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## Installation Landfill operators can install all available GCL products much faster and more easilythan 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 amountof 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 trainingfor 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 qualityassurance 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

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# 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 ConductivityAvailable 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 theproduct 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 StabilityResearch 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 theconstruction 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-scalefield 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 ProceduresStandardized 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.

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# Case Studies

T he 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 casestudies 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 linerwith 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.

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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, 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

Official Business Penalty for Private Use $300