Liner Systems for Aggressive Coal Combustion Product Leachate

The production of coal combustion products (CCPs) has grown from 59.5 million tons in 1974 to 114.7 million tons in 2013 (ACAA 2015). In 2012, approximately 60 percent of CCPs were disposed in surface impoundments and landfills. Based on the chemical composition of coal burned the coal resides (CCPs) may contain toxic substances (heavy metals), very high and low pH conditions and very high salinity. Therefore, if CCPs disposal sites do not have proper lining or cover system these toxic substances can percolate into the ground water and into the atmosphere affecting the quality of drinking water, food and air.

New regulations established for disposal of coal combustion products (CCPs) require that disposal facilities include a composite liner consisting of a geomembrane overlying a 0.6-m-thick clay liner. Alternative liner configurations are also permissible including use of a geosynthetic clay liners (GCLs) instead of a conventional clay liners (CCLs). GCLs are a popular lining material because they save airspace, can be deployed rapidly and cost-effectively and have relatively low hydraulic conductivity. New regulations have revealed many CCP waste streams that generate leachates much more concentrated than those from historical wastes. Studies have shown that conventional sodium bentonite (NaB) GCLs can be used for more dilute CCP leachates, whereas more resilient GCLs with bentonite-polymer (B-P) composites are needed for more concentrated leachates.

This research program is funded by Environmental Research & Education Foundation (EREF), the program focuses on investigating the hydraulic performance of currently available B-P GCLs against the new CCP leachates, understanding the key parameters that affect the hydraulic conductivity of B-P GCLs and developing B-P composites that can resist the aggressive CCP leachates. A wide range of permeability and chemical property tests are being conducted on B-P GCLs permeated with synthetic CCP leachates. Furthermore, factors such as effective stress and prehydration that can potentially affect the permeability of the GCLs are also being studied. It is expected that the findings from this research will help to better understand the behavior of B-P GCLs against the aggressive leachates and to develop GCL products that can give low permeability against aggressive leachates.