The report gives results of pilot field studies of flue gas desulfurization (FGD) waste disposal at Louisville Gas and Electric Co. The studies showed that properly prepared landfill from FGD sludge/fly ash mixtures can prevent trace element contamination of underlying groundwater. Analyses of leachates from the landfill impoundments studied showed that trace elements on the RCRA list of contaminants were found in concentrations below those proposed to characterize hazardous or toxic wastes. Decreasing concentrations, with time, of trace contaminants were observed in both leachate and runoff samples from the stabilized sludge mixtures. Small, synthetically lined, above-ground impoundments had higher concentrations of trace contaminants than subsurface impoundments since no attenuation by local soil was provided and vegetation that might minimize runoff was not established on these sites. Most sites developed compressive strengths significantly greater than the minimum required for recreational or light structural landfill. Water samples from beneath larger subsurface impoundments indicated that the filtering action of soil aids in decreasing the concentration of contaminants reaching the ground water supply. Certain mixtures have undergone a fixation reaction, reducing the permeability and minimizing the release of moisture and/or contaminants to the surrounding soil.