Groundwater Modeling for Closure of the Little Blue Run CCR Disposal Area

摘要

The Little Blue Run (LBR) disposal area is a 900+ acre impoundment that has been used since 1975 for the disposal of coal combustion residuals (CCR) from FirstEnergy's Bruce Mansfield Generating Station. The disposal area consists of an unlined valley fill impoundment supported by an earth and rock fill dam. The CCR materials in LBR consist of calcium sulfite scrubber material, granulated blast furnace slag, lime, and fly ash that have been hydraulically placed. A digital groundwater model was prepared for the facility to compare closure alternatives and to evaluate environmental implications of the facility after closure. The model consisted of nine layers and over 140,000 cells. It was constructed and calibrated to match observed aquifer conditions and groundwater levels within and surrounding LBR. As part of the selected long-term closure program, the CCR impoundment will be capped with a geosynthetic liner and soil cover. An anticipated result of closure is a significant drop in the water level, and subsequent settlement, within the CCR material inside the impoundment. Recognizing that significant settlement could impact the surface drainage and final cover system following closure, the groundwater model was used to predict post closure groundwater levels. A long-term simulation was run to predict the water table drawdown 50 years after the final cover system will be placed. The simulated timeline included ongoing disposal, potential site closure options, and cap system placement. The post-closure water level is predicted to drop more than 100 feet with the maximum amount occurring where the CCR deposits are the thickest. The reduction in water levels appears to be greatly dependent on the aerial extent of standing water on top of the impoundment. The majority of water drawdown within the CCR occurs within the first 24 years after closure. This analysis assisted in the selection of the final closure design for LBR.