EPA

Geosynthetic Clay Liners in 

Waste Containment

David Carson

Office of Research and Development

National Risk Management Research Laboratory

Cincinnati, OH
EPA

Contents of Presentation

uWhat is a GCL?

uWhere should GCLs be used?

uWhat are the technical issues associated with 

GCLs?

uWhat should I look for during installation of a 

GCL?

uWhat is the track record of GCL performance in 

the field?

uWhere can I learn more about GCL applications?
EPA

Common Questions

u What’s wrong with compacted clay?

u Are GCLs equivalent to CCLs in Covers and Liners?

u Aren’t GCLs too thin?

u Do plant roots penetrate GCLs?

u Are GCLs stable on slopes?

u Should GCLs be prehydrated during construction?

u Are GCLs chemically resistant?

u Are GCLs standardized?
EPA

What is a GCL?

u A composite material designed 

for hydraulic containment

» Typically 10-9, 10-10 cm/sec

u Typically comprised of 

montmorillonite clay (sodium 

bentonite) sandwiched 

between two geotextiles or 

bonded to a geomembrane

u About 1⁄4 inch in thickness, in 

panels less than 20 ft wide

Figure Courtesy of Naue Fasertechni
EPA

Where should a GCL be used?

uWaste containment cover systems

uPart of composite waste containment bottom 

liner systems - side slopes

uWhen suitable borrow soils are not available or 

economical

uTemporary or permanent secondary containment 

of tanks
EPA

Why Use a GCL in Containment?

u Consistent hydraulic properties

u Consistent engineering properties

u Relatively high manufacturer quality control

u Thin – maximizes landfill volume

u Variety of material choices to satisfy site-specific requirements

u Available at every project

u Simplified installation and construction quality control

u Some self-healing capabilities

u Simplified repair

u Simplified installation of penetrations in covers

u Cost competitive with CCLs and GMs
EPA

Bottom Liner Hydraulic 

Performance

Landfills 3 3 1 11 11 4 11 11 4

Cells 19 19 4 31 41 15 30 32 8

Maximum 104 30 0.10 126 71 29 229 158 26

Flow

Minimum 0 0 0 0.13 2.4 0 .81 0 0.02

Flow

Average 14 2.28 0.03 23 15 6.8 41 18 6.8

Flow

Life Cycle New Active Closed New Active Closed New Active Closed

Stage ->

GM/GCL GM/CCL GM Liner 

Type ->

US EPA (in print) and Othman, 1998
EPA

Bottom Liner Average Flow

0

10

20

30

40

50

flow 

(gal/acre/day)

New Active Closed

GM/GCL GM/CCL GM
EPA

GCL Types

Bentonite

Geomembrane

Geotextile

Bentonite

Geotextile

Stitching or 

Needle punching
EPA

GCL Manufacturing Process

Figure Courtesy of Naue Fasertechni
EPA

Typical MQC for GCL Materials 

Per ASTM D5889

GCL Tensile Strength D4632

GCL Clay Moisture Content D4643

GCL Index Flux D5887

GCL Clay Mass per Area D5993

Geomembrane Tensile Strength and Yield Point D638

Geomembrane Thickness D5199

Geomembrane Mass per Area D5261

Geotextile Grab Tensile Strength D4632

Geotextile Mass per Area D5261

Clay Fluid Loss D5891

Clay Free Swell D5890

Property ASTM Test Method
EPA

GCL Use in Covers

Figure Courtesy of Naue Fasertechni
EPA

Compacted Clay in Covers

uConcerns that CCL will not retain hydraulic 

properties over time

»Desiccation from above and/or below

uCracking during differential settling, freezing

uDifficult to place and compact
EPA

GCL/CCL Equivalency

uGCLs are often offered as a replacement or 

partial substitution for CCLs

uGCLs, like any other engineering material, have 

unique properties

uGCLs are not identical to CCLs, but may perform 

similarly, or outperform
EPA

GCL/CCL Equivalency

Hydraulic Issues

XL XC

Consolidation Water

XC XL

Horizontal Flow in Seams

XL XC

Horizontal Flow at GM Interface

XL

XL XC

Site 

Specific

CCL 

Advantage

Probably 

Equivalent

GCL 

Advantage

Criterion

XC

XL

XL XC

Gas Permeation

Solute Breakthrough Time

Water Breakthrough Time

XL

Chemical Absorption Capacity

Solute Steady Flux

Water Steady Flux

XL = liner application XC = cover application Adapted from Koerner et al, 1995
EPA

GCL/CCL Equivalency

Physical Issues

XC

Shrink/Swell Performance

XL XC

XL XC

Site 

Specific

CCL 

Advantage

Probably 

Equivalent

Criterion GCL Advantage

Slope Stability

XL XC

XL XC

Bearing Stability

Erosion Resistance

XL XC

Differential Settlement Tolerance

Total Settlement Tolerance

XC

Wet/Dry Performance

XL XC

Freeze/Thaw Performance

XL = liner application XC = cover application Adapted from Koerner et al, 1995
EPA

GCL/CCL Equivalency

Construction Issues

XL XC

Air Pollution Concerns

XL XC

XL XC

CCL 

Advantage

XL XC

XL XC

XL XC

GCL 

Advantage

XL XC

Weather Constraints

Site 

Specific

Probably 

Equivalent

Criterion

XL XC

Quality Assurance Requirements

Availability of Materials

Speed of Construction

Ease of Placement

Subgrade Condition Requirements

Puncture Resistance

XL = liner application XC = cover application Adapted from Koerner et al, 1995
EPA

GCL Material Selection

uPerform conformance testing, and watch to be 

sure that material tested is material delivered

uGCLs often have differing materials on either 

side with widely varying friction properties

uPlacing a GCL upside down can cause slope 

failure 
EPA

GCL Construction Issues

u GCLs are a sensitive material which requires careful 

handling and placement

» Keep protective wrap in tact while in storage

» Cover what you place at the end of every day, do not 

expose to rain

u Subgrade Preparation

» Smooth rolled surface, no ruts, cracks, footprints, 

abrupt grade changes, sticks, vegetation, sharp-edged 

stones (usually less than 1 inch diameter), construction 

debris

u CQA is critical!
EPA

GCL Construction Issues

Handling

u GCLs rolls are heavy (around 1.5 tons/roll)

» Handle with appropriate equipment

» Center tubes can crease if mishandled, damaging 

product

» GCLs arrive with 10-20% moisture from factory

u Avoid prehydration (unless non-aqueous liquids are 

contained) and dehydration

» Prehydration results in free swelling, damaging GCL if 

unconfined

» Dehydration causes material shrinkage, ruining 

overlaps (this can be masked by an overlying 

geomembrane)

— Can be made worse by GCLs with high delivered 

moisture content (or moist glues)
EPA Figure Courtesy of EPI, I

GCL Deployment
EPA

GCL Placement

Figure Courtesy of Naue Fasertechni
EPA

GCL Construction Issues

Placement

u Unload carefully and carry with caution

u Place panels according to designer’s layout

u Use a slip sheet atop textured GM

u Shingle for drainage

u Avoid vehicular traffic atop placed GCLs

» 12 inches of cover usually required for light vehicles

» Low tire pressure ATVs may be OK

u Avoid wrinkles and folds
EPA Figure Courtesy of EPI, I

GCL Placement
EPA

GCL Construction Issues

Seaming

u Most GCLs considered to be self seaming when 

overlapped

u Keep seam area clean

u Follow overlap and cover requirements of manufacturer 

or specification project), typically 15-30 cm (6-12 inches)

» Often marked on product

» Some GCL applications may require a secondary 

bentonite strip placed in seams (typically 

1/4 lb/lineal ft)
EPA Figure Courtesy of EPI, I

GCL Placement
EPA

GCL Construction Issues

u Anchoring

» Use liner anchor trench

— Some designs call for separate anchor trench

— Cover trench floor

» Remove anchoring sand bags

u Penetrations

» Use secondary GCL collars at pipe penetrations

» Detail may involve bentonite

u Repair

» Typically, extend all repair overlaps 30 cm (12 inches) 

beyond repair

» May involve bentonite and/or cement
EPA

GCL Pipe Penetration Detail

GCL

GCL

Figure Courtesy of Naue Fasertechni
EPA

Potential Cover Design Pitfalls

No composite action, vulnerability 

to puncture

GCLs placed without CCL or GM

Steep side slope (>3H:1V) Watch slope stability calcs

GCLs placed on smooth GM Poor interface friction, instability

GCLs placed atop filter fabric Poor interface friction, instability

Dry GCL is gas permeable, wet/dry 

cycling may shrink

GCL used without GM

Cover Design Feature Possible Problem(s)
EPA

Simplified Comparison of Barriers

CCL 5-22 49 3

GM 8 90 1

GCL 5-11 66 2

GM/CCL 13-30 41 2

GM/GCL/GM 18-41 37 1

GM/CCL/GM 21-38 34 2

GM/GCL 13-19 47 1

Rank in 

Group

Benefit/Cost 

Ratio*

Est. Installed 

Cost ($/m2)

Configuration

*Adapted from Daniel, 1993
EPA

The Tough Questions about GCLs

u Long-Term Performance

» Chemical Resistance

» Wet-Dry Cycling

» Freeze-thaw 

— frost protection requirements

» Seam performance

» Slope stability

u Interface shear strength, peak or residual value

u Formation of true composite with geomembrane, lateral interface 

flow 

u Material thinning after hydration

u Durability of reinforcement fibers

u Attenuation capacity
EPA

GCL Chemical Resistance

u GCLs should not be used in areas with high 

concentrations of leachable

» Calcium

» Magnesium

» Polyvalent cations

u Exposure alters geochemistry of GCLs via ion exchange 

with sodium in bentonite

u Reduces swelling capacity of bentonite, altering self 

healing capacity

u Solution: avoid applications near calcareous soil, brine, 

seawater, or use a laminated GCL product
EPA

GCL Performance in Wet/Dry Cycling

uWet/dry cycles with water is very good

uSimilar cycling when combined seasonal drying 

and/or permeation with pore water containing 

elevated salt concentrations

»Western USA, cool dry desert regions

»Eastern USA, probably calcareous soils

uFunction of confining pressure

uSolution: use a geomembrane with a GCL
EPA

GCL Freeze-Thaw Performance

uAs-manufactured GCLs appear to resist damage 

done by freeze thaw cycling in lab tests

uIn general, GCLs show far less damage than 

CCLs

uExpect higher hydraulic conductivity of hydrated 

GCLs in frost zone

uFunction of confining pressure, covers more 

susceptible
EPA

GCL Overlapped Seam Performance

uHydraulic performance is very good, especially 

for GCLs with GMs attached
EPA

GCL Recent Developments

uImproved product slope stability enhancements

uGCLs with specific chemical resistance 

properties

uPolymer modified clays in GCLs (dubbed NGCLs 

by CETCO)
EPA

Causes of Poor GCL Performance

uUnintended GCL prehydration

uInterface friction between GCL and 

accompanying material

»Poor drainage

»Improper gas management

uTraffic atop GCL causing damage

uImproper repair
EPA

Case study – GCL Bottom Liner

u Lopez Canyon MSW 

Landfill, near Los 

Angeles, CA

u 4 million m3 expansion in 

1993

u As steep as 1H:1V side 

slopes, benches every 

12m in height

u GT over GM-T over GCL

Courtesy CETCO

Shaped Surface

Operations Layer

0.6m

GCL

GM-T

GN

GT
EPA

Case study – GCL Cover

u Al Turi Landfill, Goshen, 

NY

u Vertical expansion

u 46,500 m2interim cover

u Gundseal bentonite 

protected by GM

Shaped Surface

Cover Soil

Gundseal (Bento Up)

GM-T

GN

GT

Courtesy GSE
EPA

GCL Related Research - EPA

u Field Performance of Liner Systems (in final preparation)

» GCLs have performed very well in short term

u Long-term assessment of GCL slope stability (year 7)

» GCLs stable at 3H:1V at 7 years

u Root Penetration of Unprotected GCLs

» Roots freely penetrate GCLs, but not GMs

u Permeation behavior under MSW leachate of varying age 

(for bottom containment)

» Just underway
EPA

GCL Test Plots – November 1994
EPA

Displacement Monitoring

uPlan view of gauge 

placement

uPattern repeated 

beneath crosssection

uEach plot consists of 

2 overlapping GCL 

panels
EPA

Cross Section of Displacement 

Instruments

Geonet or Sand Geomembrane

GCL

Anticipated Slip Plane

Cover Soil
EPA

Moisture Monitoring

uPlan view of probe 

location

uEach plot consists of 2 

overlapping GCL 

panels
EPA

Geosynthetic Clay Liner Research
EPA

2H:1V Disassembly – October 1999
EPA

3H:1V GCL Test Plots
EPA

EPA Publications on GCLs

u Assessment and Recommendations for 

Optimal Performance of Waste Containment 

Systems, to be finalized soon

u Geosynthetic Clay Liners Used in Municipal 

Waste Landfills, EPA/530/F-97/002

u Report of 1995 Workshop on Geosynthetic 

Clay Liners, EPA/600/R-96/149

u Report of Workshop on Geosynthetic Clay 

Liners, EPA/600/R-93/171

u Compilation of Information on Alternative 

Barriers for Liner and Cover Systems, 

EPA/600/2-91/002
EPA

Ongoing GCL Research

Outside EPA

uDOE Sandia National Lab Test Plots, 

Albuquerque, NM

uUS Bureau of Reclamation – canal lining 

performance

uGCL Manufacturer studies on product 

development and performance
EPA

Key GCL References

uDesigning with Geosynthetics, Koerner, 1998

uFinal Covers for Solid Waste Landfills and 

Abandoned Dumps, Koerner and Daniel, 1997

uGeosynthetic Clay Liners, Koerner, Gartung and 

Zanzinger, 1995

uGeotechncial Practice for Waste Disposal, edited 

by Daniel, 1993
EPA

GCL Websites

u The Geosynthetic Institute

» www.geosynthetic-institute.org

u CETCO (Bentomat, Bentofix)

» www.cetco.com

» Naue Fasertechnik

— www.naue.com, www.bentofix.com, 

www.serrot.com

u GSE (GundSeal)

» www.gseworld.com

u Huesker (NaBento)

» www.huesker.com
EPA

Questions?