Geosynthetic clay liner for coal combustion product landfill: An environmental impact assessment

Geosynthetic clay liners (GCLs) have been used in landfills for the disposal of legacy coal combustion products (CCPs); however, it remains challenging to assess environmental impacts due to leakage through landfill composite liners and to advise GCL selections for the industry and regulators. This research addresses these challenges by combining laboratory experiments, contaminant transport simulations, and environmental impact assessments to evaluate the effectiveness of landfill composite liners for legacy CCPs and to establish GCL selection thresholds based on CCP leachate chemistry. Hydraulic conductivity testing was conducted on one sodium bentonite (NaB) GCL and two bentonite-polymer composite (BPC) GCLs with different polymer contents. Those GCLs were permeated with three real CCP leachates for up to 247 days. The three leachates were all divalent-cation-rich with varying concentrations (4-115 mM) and were selected to represent aggressive CCP leachates that may have adverse impacts on GCLs. Contaminant transport simulations were conducted on landfill composite liners using the measured hydraulic conductivity and the database of CCP leachate geochemistry in the US to broaden the applicability of the results. Results show that NaB GCL can maintain low hydraulic conductivity (<8 × 10^-11 m/s) and low contaminant concentrations in the groundwater (satisfying drinking water standards) for CCP leachates with low or moderate concentrations (<80 mM). BPC GCLs are necessary for containing divalent-cation-rich and concentrated CCP leachates (>100 mM), and BPC GCLs with elevated polymer content (loss on ignition >4 %) are recommended. Application of the recommended GCLs will result in freshwater ecotoxicity of less than 5 CTUe/m² to groundwater within 100 years.