Water resources of Aurora and Jerauld Counties, South Dakota

Large quantities of slightly saline ground water are available for future water requirements in Aurora and Jerauld Counties, 1 ,236 square miles of glaciated, till-covered hills and plains in southeastern South Dakota. More than one million acre-feet of ground water is stored in five major glacial aquifers, outwash sand and gravel, beneath 340 square miles. About 58 million acre-feet is stored in bedrock, in the Niobrara marl aquifer, the Codell sandstone aquifer, and the Dakota sandstone aquifer. Recharge of aquifers by infiltration of precipitation totals 31 ,000 acre-feet annually. Effects of increased ground-water withdrawals generally have been small for glacial aquifers and large for some bedrock aquifers. Water levels declined 0.6 to 4 feet in glacial aquifers during 1978-80 within a mile of irrigation wells pumping 300 to 1,000 gallons per minute. In contrast, water levels declined 40 feet near a well pumping 1 ,500 gallons per minute from the Niobrara aquifer because of small artesian storage. Artesian pressure of the Dakota aquifer declined about 200 feet between 1909 and 1979 because of large withdrawals through flowing wells. The availability of surface water is limited because streams are ephemeral and have large flows only during spring of wet years. Most of the lakes are small, semipermanent, and shallow. Most surface water in the study area contains low concentrations of dissolved solids but most of the ground water is very hard and slightly saline. Some ground water has a very high-salinity hazard for irrigation. Water from the Niobrara and Codell aquifers also has a high sodium hazard and high boron concentrations. (USGS)