Hydraulic Conductivity of Geosynthetic Clay Liners and Compacted Clays to Leachate with PFAS

Hydraulic conductivity tests were conducted on geosynthetic clay liners (GCLs) and compacted clays using synthetic municipal solid waste (MSW) leachate containing per- and polyfluoroalkyl substances (PFAS) to determine if PFAS in MSW leachates affect hydraulic conductivity adversely. Tests were also conducted with deionized water (DIW) containing PFAS and with synthetic leachate and DIW alone to distinguish the effects of the leachate and PFAS on hydraulic conductivity. Two sodium bentonite (NaB) GCLs, one bentonite-polymer composite (BPC) GCL, and three compacted clays ranging in plasticity were evaluated to represent a range of clay barrier materials for MSW landfill liners. The synthetic leachate and DIW were spiked with three different PFAS species independently at a concentration of 1,000 ng/L (single-PFAS tests), and with a combination of seven PFAS species (multi-PFAS tests, total PFAS concentration=240,000 ng/L). Permeation was continued up to 3.3 yr. The single-PFAS and multi-PFAS tests yielded hydraulic conductivities comparable to tests with permeant solutions without PFAS (<2–4x and within reproducibility limits). One of the NaB GCLs was up to 6.8 times more permeable to synthetic leachate than to DIW, regardless of whether the permeant solution had PFAS. These findings indicate that PFAS commonly found in MSW leachates are unlikely to significantly alter hydraulic conductivity of GCLs or compacted clay liners used in MSW landfill liners.