Chemical Quality of Ground Water in the Minneapolis - St. Paul Area, Minnesota

The Minneapolis-St. Paul investigation area of about 2,500 square miles includes Hennepin, Carver, Scott, Ramsey, Washington, and parts of Anoka, Dakota, and Sibley Counties in Minnesota. Almost every formation in the area will yield some water, but only the glacial drift, the St. Peter Sandstone, the Shakopee and Oneota Dolomites, the Jordan Sandstone, the Franconia and Galesville Sandstones, and the Mount Simon and Hinckley Sandstones of Winchell (1886) yield large amounts. The yield from the Franconia and Galesville and the yield from the Mount Simon-Hinckley Sandstones are about equal to the yield from the Jordan Sandstone. Almost all the ground water in the area, as well as the surface water from representative sites is the calcium bicarbonate type. Four isocon1maps indicate that, except for recharge areas, the dissolved-solids concentrations of water from the major aquifers are lowest in the eastern or northeastern part of the area and highest in the western or southern part. The isocon maps can be used together with a system of curves and bar graphs to predict the quality of the water that is likely to be obtained from the major aquifers in the basin. A comparison of chemical analyses from 1899 to 1963 for the major aquifers indicates little natural change in the chemical quality of the water. In some areas, contamination of water in shallow aquifers could have an effect on the quality of the water in the deeper aquifers. Hardness, dissolved solids, iron, manganese, and bicarbonate probably have the greatest effect on the suitability of water for most uses.