POTENTIAL GEOTHERMAL RESOURCES ON MINED LANDS

Large volumes of shallow free-flowing ground water suitable for use in geothermal heat-pump systems exist in Indiana and neighboring states. Waters from abandoned underground coal and limestone mines are used for heating or cooling homes, businesses, and even small towns in other countries—such as Springhill, Nova Scotia. A few examples of extracting heat from mine waters also occur in the United States. Indiana has more than 194,000 acres underlain by abandoned underground coal mines, and more than 50,000 acres mined for aggregate stone. An estimated 170 billion gallons of water are contained in underground mines. A significant amount of water also occurs in surface mined areas. Underground waters in Indiana are generally about 52^o to 54^o Fahrenheit, therefore mined areas contain a significant source of low-temperature geothermal waters that could be used to lower costs and enhance efficiency of ground-coupled heat pumps. Heat could easily be extracted without disturbing mine pool waters by using thermal loops or even with in-mine heat exchangers. Because mine water characteristics vary, research to determine water quality, quantity, and heat content is needed to select the best areas for geothermal mine water exploitation. Near-surface coal mine waters can have high TDS, low pH, and other quality issues. Deeper waters are often of relatively good quality but may contain sodium sulfate.

In addition to static water, many millions of gallons of ground water are pumped to the surface each day during mining of coal or aggregates. Additional warm waters are available from petroleum production as produced waters. Such waters have temperatures near those of underground waters in static mine pools. Extraction of heat from pumped waters coming from active mine or petroleum operations could also become an important source of low-temperature geothermal energy.