Hydraulic conductivity of geosynthetic clay liners to trona ash leachate: Effects of mass per unit area, bundles of fiber existence, and preydration conditions.

• Trona ash leachate (TAL) has high ionic strength among coal combustion leachates. • Hydraulic conductivity to TAL is high at low GCL mass per unit area (MPUA). • Hydraulic conductivity to TAL is low at MPUA of 5.0 kg/m2. • Bundles of fibers play an important role on hydraulic conductivity at low MPUAs. The barrier performance of geosynthetic clay liners (GCLs) to coal combustion products (CCPs) is of primary importance. One of the CCPs leachates that has a damaging effect on hydraulic conductivity is trona ash leachate (TAL). In this study, the hydraulic conductivity of sodium GCL (Na-GCL) to TAL was investigated in terms of mass per unit area (MPUA). The hydraulic conductivity of GCLs to TAL was 2.6 × 10-6 and 7.6 × 10-7 m/s when the MPUA was 3.0 kg/m2 (M b3) and 4.0 kg/m2 (M b4), respectively. Dye tests conducted on these GCLs showed that flow preferentially occurred through bundles of fibers existing in the GCLs. In contrast, increasing the MPUA to 5.0 kg/m2 (M b5) led to a decrease in the hydraulic conductivity (i.e. 4.1 × 10-11 m/s). Additional tests were performed on fiber-free GCLs to determine the role of fiber bundles. Regardless of MPUA, the fiber-free GCLs had low hydraulic conductivity (6.7 × 10-11 m/s). Prehydrating M b3 and M b4 with deionized water (DIW) before permeation with TAL also decreased the hydraulic conductivity. The hydraulic conductivities of prehydrated M b3 and M b4 were 1.6 × 10-10 and 4.8 × 10-11, respectively. Chemical analyses showed that the cation exchange reaction had a negligible influence on the hydraulic conductivity. Because TAL was a potential source of Na+ throughout the tests. [ABSTRACT FROM AUTHOR]