Ground-Water Flow and Quality in A Fully Flooded Underground Complex

Abstract

Water quantity and quality conditions are described for a mine-pool aquifer in a fully flooded complex of underground mines in northern West Virginia. Abandoned mines in the Pittsburgh coal bed are contiguous, and separated by coal barrier pillars ranging from as little as 9 to about 60 meters thick. Barrier pillars are transmissive enough to circulate significant quantities of water between mines, yet they control head distribution and flow direction within the aquifer. The mine-pool acts as a partly confined to confined aquifer, and recharge is approximately balanced by withdrawal of about 5700 Liters/minute, leakage to adjacent mines, and unquantified outflow to unmined areas. Resulting drawdown prevents the mine-pool from discharging directly into overlying streams. A centrally located subgroup of mines within the aquifer currently acts as a ground-water sink, but water levels are slowly increasing in the sink, and in some outflow areas. Mine waters are highly reduced, with circumneutral pH, and variable Fe concentrations from 5 to over 100 mg/L. Total alkalinity averages about 200 mg/L with a mixed Ca-Na-HCO3-SO4 composition in recharge areas. End of flow path waters contain up to 600 mg/L alkalinity, and are Na-SO4 type waters with higher dissolved solids and metals concentrations. The shift from Ca to Na dominated waters is attributed mainly to cation exchange. Potentiometric head is increasing in the aquifer, and mine-pool withdrawal may have to be increased to prevent discharge to the surface. Mine-pool quality remains poor, and has shown slow improvement in 6 years of monitoring.