BURIED KARST HYDROGEOLOGY OF THE PLATTEVILLE FORMATION, TWIN CITIES, MINNESOTA

Much of the Minneapolis-St. Paul metropolitan area is underlain by subcropping Platteville Formation, a predominantly fossiliferous micrite. Although its total thickness is approximately 32 feet, its transmissivity has been found by the author to range from 5 to 200,000 ft²/day. This range is in part due to the different, characteristic hydraulic conductivities of the five members comprising the Platteville. These are, in ascending order, the Pecatonica, Mifflin, Hidden Falls, Magnolia, and Carimona members. It is also in part due to the solution enlargement both of stratigraphic horizons of particular layers, principally in the Magnolia, and of joints. The results of hydrogeologic investigations of several locations within the Twin Cities Metropolitan Area will be described, showing characteristic patterns of permeability distribution and the effect on the groundwater flow system within the Platteville and the overlying unconsolidated deposits.