Hydraulic Conductivity of Geosynthetic Clay Liners to Synthetic Coal Combustion Product Leachates

Abstract

Experiments were conducted to evaluate whether coal combustion product (CCP) leachates adversely affect the hydraulic conductivity of geosynthetic clay liners (GCLs). Chemical properties of CCP leachates were compiled based on a nationwide survey of CCP disposal facilities. Five synthetic leachates were selected from this database to represent a range of conditions encountered in CCP disposal facilities: typical CCP leachate, strongly divalent cation fly ash leachate, flue gas desulfurization (FGD) residual leachate, high ionic strength ash leachate, and trona ash leachate. Five GCLs were tested: two conventional Na-bentonite GCLs, two polymer-modified bentonite GCLs, and one bentonite polymer composite (BPC). Hydraulic conductivity tests were conducted on non-prehydrated GCLs using flexible-wall permeameters. GCLs with Na-bentonite had high hydraulic conductivity (>10 m/s) to trona leachate, whereas the hydraulic conductivity of GCLs with polymer-modified bentonite was variable, ranging from 10 to 10 m/s. For the typical CCP, high ionic strength, FGD, and strongly divalent cation leachates, GCLs with Na-bentonite had moderate to high hydraulic conductivity (10 to 10 m/s). GCLs with polymer-modified bentonite had lower hydraulic conductivity (10 to 10 9 m/s) to FGD and strongly divalent cation leachates, and a wide range of hydraulic conductivities to high ionic strength leachate (10 to 10 m/s). All of the GCLs had low hydraulic conductivity (<10 m/s) to DI water. GCLs with BPC had very low hydraulic conductivity (< 10 m/s) to all leachates.