Characterization of Indiana’s Coal-Mine Aquifer

Abstract

Almost 200,000 acres of Indiana are underlain by abandoned underground coal mines. Many of the voids are filled with water, representing a high-yield aquifer that may contain 170 billion gallons or more. Since 1984, the Indiana Geological Survey has gathered data on storativities, long-term potentiometric water levels, and the hydrochemistry of six abandoned underground mines scattered across southwestern Indiana. These data indicate that the mines exhibit a wide variety of hydrologic and chemical characteristics. Concentrations of sulfate range from 3 to 20,000 mg/l, while concentrations of acidity and alkalinity range from 0 to 8,800 mg/l and 0 to 2,500 mg/l, respectively, and pH values range from 3.5 to 9.2. Values of storativity range from 0.0003 to 0.003, and barometric efficiencies range from 0.27 to 0.83. Long-term potentiometric levels show no evidence of seasonality or other long-term periodicities, and records indicate that several mines are still being hydrologically influenced by human activities long after their abandonment. Future development of the coal-mine aquifer for a variety of beneficial purposes, such as new groundwater supplies or sources of geothermal energy, will require consideration of potentially adverse secondary results, including the possibility of increased generation of acid mine drainage caused by dewatering of voids and increased risk of subsidence.