Long-term hydraulic conductivity of bentonite-polymer geosynthetic clay liners

Hydraulic conductivity tests were conducted on six bentonite-polymer (B-P) geosynthetic clay liners (GCLs) to investigate the effect of the slow cation exchange process and polymer elution on the long-term hydraulic conductivity of B-P GCLs. Tests were conducted up to 1458 days and as many as 443 pore volumes of flows (PVFs). Three B-P GCLs consist of linear polymer whereas the other three have crosslinked polymer. One sodium geosynthetic clay liner (Na-B GCL) was used as a control. Hydraulic conductivities (K6766) of B-P GCLs (5.4 x 10-12 m/s to 3.7 x 10-11 m/s) per ASTM D6766 were approximately 2-3 orders of magnitude lower than that of Na-B GCL (2.3 x 10-9 m/s to 3.5 x 10-9 m/s). Tests were continued after hydraulic and chemical equilibrium to investigate the long-term hydraulic conductivity of GCLs. Hydraulic conductivities of GCLs had an increasing trend after hydraulic and chemical equilibrium. The ratio of KL/K6766 for B-P GCLs was 3.5-14.7, whereas ratio of KL/K6766 for Na-B GCLs was 1.0-1.7. Total organic carbon (TOC) tests results confirmed that polymer elution occurred during the entire permeation process. The higher ratio of KL/K6766 for B-P GCLs was attributed to the effect of polymer elution.