Hydraulic conductivities and effective diffusion coefficients of geosynthetic clay liners with organobentonite amendments

Laboratory diffusion and hydraulic conductivity testing were performed on GCLs amended with two different types of organobentonites: Benzyltriethylammonium-bentonite (BTEA-bentonite) and hexadecyltrimethylammonium-bentonite (HDTMA-bentonite) and compared to results for a GCL constructed with conventional sodium bentonite. Results from the hydraulic conductivity testing indicate the addition of both types of organobentonite results in an increase in hydraulic conductivity. Only a small increase in hydraulic conductivity was observed for both types of amended GCLs up to 20% organobentonite amendment. At higher organobentonite contents, measured hydraulic conductivity for both types of amended GCLs rose by as much as three orders of magnitude. The effective diffusion coefficient of [³H]water measured for both the organobentonite-amended GCLs and a laboratory-constructed sodium bentonite GCL were similar and ranged from 3.6 × 10^-10 to 5.0 × 10^-10 m²/s. One-dimensional benzene solute transport simulations were performed to determine how the observed changes in hydraulic conductivity and diffusion coefficients would affect organic solute transport when coupled with the increased sorptive capacity of the organobentonite-amended GCLs. In general, GCLs modified with BTEA-bentonite resulted in a significant reduction in benzene flux through the GCL compared to the conventional GCL. However, modifying the GCL with HDTMA-bentonite resulted in an increase in solute transport when compared to the conventional GCL.