Groundwater Flow Modeling of an Abandoned Mine Lands Site Scheduled for Reclamation

Abstract

Groundwater flow models represent one tool that can be used in evaluating the hydrologic conditions of abandoned mine land (AML) sites, and they can be used to preview the probable hydrologic outcomes of reclamation designs. A three-dimensional, variably saturated groundwater flow model was used to characterize the hydrology of a 47 ha AML site in southwestern Indiana. Of particular concern was the flow field extending through a tailings deposit to a large seep contributing acid mine drainage to the local stream. The model was then used to evaluate a potential reclamation plan that would redirect the acidic flow into an onsite lowland area for passive treatment.

A transient model was calibrated by adjusting the model parameters until a minimum residual was achieved between simulated and observed water table elevations in 6 observation wells over a time period of 50 days. The best-fit model had a root mean squared error (RMSE) of 0.195 m. Modeling results show that the seep is fed from a ground watershed of approximately 7.7 ha which spans across the tailings into the coarse-grained refuse bordering the deposit. Further results show that minor alterations of surface topography within the tailings deposit could potentially redirect and contain the acidic groundwater on site for passive treatment prior to discharging into the local drainage network. This study demonstrates the utility of using groundwater flow models to preview hydrologic conditions at AML sites and to anticipate the results of reclamation alternatives.