Geochemistry of an Abandoned Landfill Containing Coal Combustion Waste: Implications for Remediation

Abstract

The 488-D Ash Basin (488-DAB) is an unlined, earthen landfill containing approximately one million tons of dry ash and coal reject material at the U.S. Department of Energy’s Savannah River Site, SC. The pyritic nature of the coal rejects has resulted in the formation of acidic drainage (AD), which has contributed to groundwater deterioration and threatened biota in adjacent wetlands. Establishment of a dry cover is being examined as a remedial alternative for reducing AD generation within this system by minimizing the contact of oxygen and water to the waste material. To determine the potential benefit of a cover on pore water chemistry, a series of flow-through column experiments were performed under varying environmental conditions using materials from the site. The experiment was designed to demonstrate the influence of temperature, gaseous composition (dissolved nitrogen vs. oxygen), and flow regime (continuous flow vs. episodic wetting/drying) on effluent chemistry. Results indicated that the fluid composition (e.g., pH, redox, elemental composition) was closely associated to dissolved and/or gaseous oxygen content and wetting regime. Given these conditions, the use of a dry cover could reduce the production of acid lechate over time, pending that it retards or eliminates fluid and oxygen transport to the subsurface.