Hydraulic conductivity of bentonite-polymer geosynthetic clay liners to aggressive solid waste leachates

Hydraulic conductivity of conventional mock sodium bentonite (Na–B) and bentonite-polymer (B–P) geosynthetic clay liners (GCLs) were evaluated with three synthetic leachates that are chemically representative of aggressive leachates from coal combustion product (CCR) (I = 3179 mM), mining waste (MW) (I = 2127 mM, pH = 2.0), and municipal solid waste incineration ash landfill (MSWI) (I = 2590 mM). The mock B–P GCLs were created by dry mixing bentonite with branched, linear, or crosslinked polymer. The polymer loading of mock B–P GCLs ranged from 3 to 15%. Comparative tests were also conducted with Na–B GCLs. The mock Na–B GCLs cannot maintain low hydraulic conductivity to aggressive CCR, MW, and MSWI leachates. Mock B–P GCLs with 10% branched polymer had low hydraulic conductivity (< 1.0 × 10⁻¹⁰ m/s) to synthetic MW and MSWI leachates at 20 kPa effective confining stress, whereas the hydraulic conductivity of mock B–P GCLs with 10% linear or crosslinked polymer ranged from 1.5 × 10⁻⁹ to 1.4 × 10⁻⁷ m/s. As the effective stress increased, the B–P GCLs branched polymer showed a faster decreasing trend than that of Na–B and B–P GCLs with linear or crosslinked polymer.