Factors Affecting Water-Supply Potential of the Twin Cities Metropolitan Area Aquifer System

ABSTRACT-The Twin Cities aquifer system in Minnesota contains five aquife~s and fou: confining units that together consist of fourteen geologic units. Unconsolidated sand and gravel aqmfers overlie bedrock sandstone and carbonate aquifers. Between 1880 and 1980, groundwater wi_thdrawals have c_aused long-term wate~ level declines of as much as 90 feet in the Prairie du Chien-Jordan aquifer and 240 feet m the deeper Mount S~monHinckley aquifer-the two major sources of groundwater supplies in the ar~a .. The estimated max1mu1:1 continuous withdrawal rate from the aquifer system is about 650 Mgal/d (million gallons per day). This compares with an average daily groundwater use on an annual basis of a~out 20~ Mgal/d from the l_ate 1970s through 1986, the last year of normal precipitation. Increas~d costs of w1t?drawmg ground water, mcreased risks of decreased groundwater quality, and increased conflicts between s1multaneo~s ~sers of gr_oundwater resources are associated with increased rates of groundwater with~rawal. The prmc1p~l physical factors affecting water-supply potential are those that control the rate at which water may be withdrawn from the Mississippi River and the Twin Cities aquifer system