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By using ground source heat pumps to exchange heat with the shallow surface, areas with minimal or no tectonic activity can still be viable resources for low-temperature geothermal energy. This study focuses on generally characterizing the potential exploitation of flooded mines as low-temperature thermal resources within Ohio. These unconventional thermal resources offer large, thermally stable bodies of water, which store relatively more heat than saturated soils and bedrock. The legacy of underground mining, predominantly in the southeastern and eastern portions of Ohio, makes ground source heat pump geothermal energy a potentially valuable resource for the state. Using geographic information system (GIS) software, mines that were either flooded or partially flooded and within 1.6 km of a population center were selected as potential candidates for ground source heat pump exploitation. Physical and thermal parameters were calculated for each of the identified geothermal sites. These include: maximum and minimum residence times of waters within the mines, maximum and minimum recharge to the mines, effective mine volumes, linear groundwater velocities, groundwater flow direction, and percentage of the mine that is flooded. The total theoretical amount of heat extraction or addition per degree change in mine water temperature (Celsius degree) was calculated for each identified mine site, as well as the potential amount of heat either entering or being dissipated in mine waters due to groundwater recharge.

This study identified 147 possible mine sites spanning 21 counties that might be used for ground source heat pump installations in Ohio. The mines have an estimated average maximum residence time ranging from 6 to 15 yr and an estimated average minimum residence time ranging from 3.6 to 8.9 yr. It was estimated that, on average, 1010 kJ °C−1 of heat energy could be extracted from the mines. Overall, this study has shown that abandoned underground mines contain enough stored heat to be used as thermal resources for ground source heat pump systems, and that the number and extent of mines within Ohio could make this type of geothermal resource valuable.

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