Three different types of geosynthetic clay liners (GCLs) were used in this study in terms of bentonite inside of the GCLs. These GCLs are polymer bentonite (PB GCL), 50% attapulgite + 50% Na-bentonite (%50A + %50NaB GCL) and 50% attapulgite + %50 polymer bentonite (50%A + 50%PB GCL). Different prehydration conditions were applied during the study. That is, GCLs were subjected to hydration with no-prehydration (non-prehydrated), 24h (or 1 day)-prehydration (prehydrated) and 30days of hydration over compacted zeolite (prehydrated over zeolite). The prehydration had little influence on the hydraulic conductivity of PB GCL and 50%A + 50%PB GCL when DIW was the permeant. The hy-draulic conductivities for these GCLs did not depend on the prehydration condition and were around 5.8×10-11 m/s and 1.5×10-10 m/s, respectively. In contrast, hydraulic conductivity of %50A + %50NaB GCL hydrated over compacted zeolite was about four orders of magnitude less than non-prehydrated %50A + %50NaB GCL. In the case of permeating with 50 mM CaCl2 solution, the prehydration had significant effect on the hydraulic conductivity of PB GCL and 50%A + 50%PB GCL. The hydraulic conductivity reduced by the prehydration from 4.9×10-7 m/s to 1.6×10-7 m/s for PB GCL and from 1.6×10-6 m/s to 1.5×10-8 m/s for 50%A + 50%PB GCL. At this time, however, the hydraulic conductivity of prehydrated 50%A + 50%PB GCL was an order of magnitude less than the hydraulic conductivity of PB GCL, indicating adding attapulgite into bentonite may not have an influence when the permeant is other than DIW.
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