Hydraulic Conductivity of Geosynthetic Clay Liners Exhumed from Landfill Final Covers with Composite Barriers
Publication: Journal of Geotechnical and Geoenvironmental Engineering
Volume 137, Issue 1
Abstract
Geosynthetic clay liners (GCLs) were exhumed from composite barriers, (i.e., geomembrane over GCL) in final covers at four sites after 4.7 to 6.7 years to evaluate the in-service condition. Monovalent bound cations were replaced by divalent cations in all GCLs, with near complete exchange at two-thirds of the sampling locations. Hydraulic conductivity was measured using two dilute solutions commonly used as permeant water: standard water (SW, solution) and type II deionized water (DW). Hydraulic conductivities to SW varied over four orders of magnitude, whereas identical specimens (i.e., from same sample) had hydraulic conductivities to DW consistently . Higher hydraulic conductivities and sensitivity to permeant water did not correspond directly to the amount of cation exchange. Exhumed GCLs with higher gravimetric higher water contents exhibited a gel structure indicative of osmotic hydration and had lower hydraulic conductivities to both SW and DW, regardless of the amount of sodium (Na) replaced by divalent cations. These GCLs with higher water contents were placed on subgrade having water content in excess of optimum water content (standard Proctor). Conditions that promote rapid hydration and osmotic swell in a GCL are recommended to ensure that a GCL in a composite barrier maintains low hydraulic conductivity , even if the native Na is ultimately replaced by divalent cations. Subgrade with water water content is recommended.
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Acknowledgments
A consortium consisting of the National Science Foundation (Grant No. NSFCMMI-0625850), the U.S. Nuclear Regulatory Commission, the U.S. Environmental Protection Agency, the U.S. Department of Energy, the Environmental Research and Education Foundation, Colloid Environmental Technologies Corporation, Veolia Environmental Services, and Waste Connections, Inc. provided financial support for this study. This support is gratefully acknowledged. The findings and recommendations in this report are solely those of the writers, and do not necessarily represent the policies or opinions of the sponsors. Endorsement by the sponsors is not implied and should not be assumed.
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Information
Published In
Journal of Geotechnical and Geoenvironmental Engineering
Volume 137 • Issue 1 • January 2011
Pages: 1 - 13
Copyright
© 2011 ASCE.
History
Received: Jul 22, 2009
Accepted: Jun 9, 2010
Published online: Jun 29, 2010
Published in print: Jan 2011
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