Hydraulic Conductivity of Compacted Soil Liners Permeated with Coal Combustion Product Leachates

Tests were conducted on eight soils to determine how coal combustion product (CCP) leachates may affect the hydraulic conductivity of compacted soil liners (CSLs) used for CCP disposal facilities. The soils represent a broad range of particle-size distributions, Atterberg limits, and mineralogy, and meet minimum compositional recommendations for CSLs. Hydraulic conductivity tests were conducted with five characteristic CCP leachates from the Electric Power Research Institute (EPRI) database of CCP leachates. The testing confirmed that seven of the soils are suitable for a CSL. Five of the seven suitable soils have hydraulic conductivity<1x10-9m/s when permeated with any of the CCP leachates at 28kPa effective stress (disposal facility with first lift of CCP placed), as do all but one soil when the effective stress is 450kPa. Larger increases in hydraulic conductivity are associated with soils having lower hydraulic conductivity to deionized water and significant montmorillonite content. Soils exhibiting the smallest increases in hydraulic conductivity have little to no montmorillonite. Hydraulic conductivity to CCP leachate is not related systematically to any of the primary index properties, indicating that mineralogy is a better indicator of sensitivity to CCP leachates than index properties. Increasing the effective stress from 28 to 450kPa (approximate to 2 to 30m CCP depth) results in an average reduction hydraulic conductivity of 10x. The average reduction is 2x at 100kPa and 5x at 250kPa.