For five different Geosvnthetic Clay Liners (GCLs) examined, results show that at relatively low stresses, the type o f GCL manufacturing process may affect the final bulk void ratio of a GCL (ee) produced after hydration. Previous research has shown that the hydraulic conductivity is related to e_B, and it was postulated that diffusion coefficients may also be related to e_B.

Apparatus and procedure for performing tests to obtain inorganic diffusion coefficients for GCLs are described and the processes that can affect the interpretation of these tests are discussed. The diffusion coefficients deduced from GCL diffusion tests performed with 0.05 M to 0.08 M NaCl solutions decrease linearly with decreasing final bulk GCL void ratio. However, when the NaCl concentration is increased significantly, the diffusion coefficient deduced is also shown to increase. As the NaCl concentration increases above 0.6 M. a constant stress applied to the sample is shown to mitigate increases in diffusion coefficients compared to the case of the sample being tested at a constant void ratio.

Aromatic and chlorinated organic compound sorption of the bentonite component of the GCL and various bentonites additives is examined. GCL diffusion tests are also performed to quantify the diffusion and sorption of these compounds through a bentonite GCL. The use of various bentonite additives is shown to improve the sorption of the bentonite in GCLs.

A field study is presented which examines the performance of a geomembrane (GM) compacted clay (CCL) composite liner for a landfill leachate lagoon decommissioned 14 years after construction. Approximately 600 defects present on the GM were apparently sufficient to cause leachate to migrate between the GM and CCL. Pore-water profiles through the CCL for chloride, sodium, and potassium combined with advective-diffusive contaminant transport modelling suggest that the GM component of the composite liner did not perform well as a barrier.