The impact of leachate from clean coal technology waste on the stability of clay and synthetic liners. Topical report, March 1, 1995--March 31, 1996

Abstract

This project was developed to provide design criteria for landfill disposal sites used for sludges such as those generated using the Clean Coal Technologies (CCT) tested at the Public Service Company of Colorado`s Arapahoe Power Plant. The CCT wastes used were produced at the Arapahoe Plant Unit No. 4, which was equipped with the integrated dry NO{sub x}/SO{sub 2} emissions control system installed under the Clean Coal Technology Program. The investigation emphasized the potential impact of clean coal technology materials (sodium and calcium injection systems and urea injection) on the permeability and stability characteristics of clay liner materials and the stability of synthetic liner materials. Flexible-wall permeameters were used to determine the hydraulic conductivities (HC) of the clay liner materials affected by various compactive conditions. Tests were conducted using the waste materials overlying the clay liner materials through wet/dry cycles, freeze/thaw cycles, and over 120-day periods. The impact of CCT materials on the characteristics of the clay liner materials studied in this project was minimal. The HC measurements of the waste/clay liner systems were similar to those of the water/clay liner systems. HC decreased for clay liners compacted at moisture levels slightly higher than optimum (standard Procter) and increased for liners compacted at moisture levels lower than optimum (standard Procter). Although some swelling was evident in the sodium materials, the sludge materials did not have a negative impact on the integrity of the liners over 120-day tests. Wet/dry cycles tended to result in lower HC, while freeze/thaw cycles substantially increased HC for the liners tested.