Groundwater Modeling for Closure of the Little Blue Run CCR Disposal Area
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 draw-down 50 years after the final cover system will be placed. The simulated timeline included disposal, site closure options, and liner 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 areal 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.