### 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 u 

### What is a GCL? u 

### Where should GCLs be used? u 

### What are the technical issues associated with GCLs? u 

### What should I look for during installation of a GCL? u 

### What is the track record of GCL performance in the field? u 

### Where 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 Fasertechnik

### EPA 

## Where should a GCL be used? u 

### Waste containment cover systems u 

### Part of composite waste containment bottom liner systems - side slopes u 

### When suitable borrow soils are not available or economical u 

### Temporary 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**

4 11 11 4 11 11 1 3 3 Landfills 8 32 30 15 41 31 4 19 19 Cells 26 158 229 29 71 126 0.10 30 104 Maximum Flow 0.02 0 .81 0 2.4 0.13 0 0 0 Minimum Flow 6.8 18 41 6.8 15 23 0.03 2.28 14 Average Flow Closed Active New Closed Active New Closed Active New Life Cycle Stage - > 

### GM GM/CCL GM/GCL Liner Type - >

US EPA (in print) and Othman, 1998

### EPA 

## Bottom Liner Average Flow

0 10 20 30 40 50flow(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 Fasertechnik

### EPA **Typical MQC for GCL Materials Per ASTM D5889** 

D4632 GCL Tensile Strength D4643 GCL Clay Moisture Content D5887 GCL Index Flux D5993 GCL Clay Mass per Area D638 Geomembrane Tensile Strength and Yield Point D5199 Geomembrane Thickness D5261 Geomembrane Mass per Area D4632 Geotextile Grab Tensile Strength D5261 Geotextile Mass per Area D5891 Clay Fluid Loss D5890 Clay Free Swell ASTM Test Method

Property

### EPA 

## GCL Use in Covers

Figure Courtesy of Naue Fasertechnik

### EPA 

## Compacted Clay in Covers u 

### Concerns that CCL will not retain hydraulic properties over time » Desiccation from above and/or below u 

### Cracking during differential settling, freezing u 

### Difficult to place and compact

### EPA 

## GCL/CCL Equivalency u 

### GCLs are often offered as a replacement or partial substitution for CCLs u 

### GCLs, like any other engineering material, have unique properties u 

### GCLs are not identical to CCLs, but may perform similarly, or outperform

### EPA 

## GCL/CCL Equivalency **Hydraulic Issues**

X L XC Consolidation Water X L XC Horizontal Flow in Seams X L XC Horizontal Flow at GM Interface X L X L XC Site Specific CCL Advantage Probably Equivalent GCL Advantage Criterion

XC X L X L XC

Gas Permeation Solute Breakthrough Time W ater Breakthrough Time X L Chemical Absorption Capacity Solute Steady Flux W ater Steady Flux

X L = liner application XC = cover application Adapted from Koerner et al, 1995

### EPA 

## GCL/CCL Equivalency **Physical Issues**

XC Shrink/Swell Performance

X L XC X L XC Site Specific CCL Advantage Probably Equivalent GCL Advantage Criterion

Slope Stability X L XC

X L XC Bearing Stability Erosion Resistance X L XC Differential Settlement Tolerance Total Settlement Tolerance XC Wet/Dry Performance X L XC Freeze/Thaw Performance

X L = liner application XC = cover application Adapted from Koerner et al, 1995

### EPA 

## GCL/CCL Equivalency **Construction Issues**

X L XC Air Pollution Concerns X L XC X L XC CCL Advantage

X L XC X L XC X L XC GCL Advantage

X L XC Weather Constraints Site Specific Probably Equivalent Criterion

X L XC Quality Assurance Requirements Availability of Materials Speed of Construction Ease of Placement Subgrade Condition Requirements Puncture Resistance

X L = liner application XC = cover application Adapted from Koerner et al, 1995

### EPA 

## GCL Material Selection u 

### Perform conformance testing, and watch to be sure that material tested is material delivered u 

### GCLs often have differing materials on either side with widely varying friction properties u 

### Placing 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, Inc. 

## GCL Deployment

### EPA 

## GCL Placement

Figure Courtesy of Naue Fasertechnik

### 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, Inc. 

## 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, Inc. 

## 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 Fasertechnik

### EPA 

## Potential Cover Design Pitfalls

No composite action, vulnerability to puncture GCLs placed without CCL or GM Watch slope stability calcs Steep side slope (>3H:1V) Poor interface friction, instability GCLs placed on smooth GM Poor interface friction, instability GCLs placed atop filter fabric Dry GCL is gas permeable, wet/dry cycling may shrink GCL used without GM Possible Problem(s) Cover Design Feature

### EPA 

## Simplified Comparison of Barriers

3 49 5 - 22 CCL 1 90 8 GM 2 66 5 - 11 GCL 2 41 13 - 30 GM/CCL
1 37 18 - 41 GM/GCL/GM 2 34 21 - 38 GM/CCL/GM 1 47 13 - 19 GM/GCL Rank in Group Benefit/Cost Ratio* Est. Installed Cost ($/m 2) 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 u 

### Wet/dry cycles with water is very good u 

### Similar 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 u 

### Function of confining pressure u 

### Solution: use a geomembrane with a GCL

### EPA 

## GCL Freeze **- Thaw Performance**  u 

### As - manufactured GCLs appear to resist damage done by freeze thaw cycling in lab tests u 

### In general, GCLs show far less damage than CCLs u 

### Expect higher hydraulic conductivity of hydrated GCLs in frost zone u 

### Function of confining pressure, covers more susceptible

### EPA 

## GCL Overlapped Seam Performance u 

### Hydraulic performance is very good, especially for GCLs with GMs attached

### EPA 

## GCL Recent Developments u 

### Improved product slope stability enhancements u 

### GCLs with specific chemical resistance properties u 

### Polymer modified clays in GCLs (dubbed NGCLs by CETCO)

### EPA 

## Causes of Poor GCL Performance u 

### Unintended GCL prehydration u 

### Interface friction between GCL and accompanying material » Poor drainage » Improper gas management u 

### Traffic atop GCL causing damage u 

### Improper repair

### EPA 

## Case study **– GCL Bottom Liner**  u Lopez Canyon MSW Landfill, near Los Angeles, CA u 4 million m 3 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 m 2 interim 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 u 

### Plan view of gauge placement u 

### Pattern repeated beneath cross section u 

### Each 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 u 

### Plan view of probe location u 

### Each 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** u 

### DOE Sandia National Lab Test Plots, Albuquerque, NM u 

### US Bureau of Reclamation – canal lining performance u 

### GCL Manufacturer studies on product development and performance

### EPA 

## Key GCL References u 

### Designing with Geosynthetics , Koerner, 1998 u 

### Final Covers for Solid Waste Landfills and Abandoned Dumps, Koerner and Daniel, 1997 u 

### Geosynthetic Clay Liners , Koerner, Gartung and Zanzinger, 1995 u 

### Geotechncial 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?