SOUTH DAKOTA GEOTHERMAL RESOURCES

South Dakota is normally not thought of as a geothermal state. However, geothermal direct use is probably one of the best kept secrets outside the state. At present there are two geothermal district heating systems in place and operating successfully, a resort community using the water in a large swimming pool, a hospital being supplied with part of its heat, numerous geothermal heat pumps, and many individual uses by ranchers, especially in the winter months for heating residences, barns and other out building, and for stock watering. GEOLOGY AND RESOURCE BACKGROUND The best known and most significant geothermal resource in the state is the Madison Limestone. It is well known as an aquifer and oil producing formation throughout the northern Great Plains and Rocky Mountains. The Madison (also known as the Pahasapa) contains about 179 miles3 (746 km3) of recoverable water with temperatures range from about 86oF to 216oF (30oC to 102oC) and a mean resource base is 2.78 x 1018 Btu (2,930 x 1018 J) (Gosnold, 1987 and revised in 1991). The Madison is one of the two geothermal aquifers that are presently used in direct-heat applications. The other is the Newcastle-Dakota Sandstone. Recent work, including eight potential geothermal aquifers, estimate the accessible geothermal resource base (about 0.001 times the resource base) of South Dakota as 12.52 Exajoules (1018) or 11.88 quads as shown in Table 1 (Gosnold, 1991)