Effects of present and projected ground-water withdrawals on the Twin Cities aquifer system, Minnesota

Abstract

The Twin Cities aquifer system in Minnesota contains 5 aquifers and 4 confining units composed of 14 stratigraphic units. Bedrock aquifers consist of friable sandstones and highly fractured carbonate rocks; aquifers in the glacial drift consist of outwash and alluvium. From 1880 to 1980, groundwater withdrawals had caused long-term declines of water levels of as much as 90 feet in the Prairie du Chien-Jordan aquifer and 240 feet in the deeper Mount Simon-Hinckley aquifer-the two major sources of groundwater supplies in the area. A steady-state model of groundwater flow was used successfully to simulate the potentiometric surfaces of the aquifers during the 1970's. assuming a withdrawal rate of about 190 million gallons per day from the entire system. Projected changes in population and industrial development suggest that future groundwater withdrawals may increase from those for the 1970's. Steady-state model results indicate that the potentiometric surface of the Mount Simon-Hinckley aquifer would be lowered as much as 400 feet if pumpage from that aquifer were increased by 125 percent above 1980 groundwater withdrawal rates of about 200 million gallons per day. The potentiometric surface of the Prairie du Chien-Jordan aquifer also would be lowered as much as 400 feet if pumpage from that aquifer were increased by 200 percent above 1980 groundwater withdrawals of 160 million gallons per day. Given the projected distribution of future groundwater development, and the limitations inherent in simulating groundwater flow, the model results indicate that an approximate limit of groundwater availability in the Twin Cities Metropolitan Area, Minnesota, is from about 500 to 800 million gallons per day.