The Mount Simon-Hinckley aquifer in southeast Minnesota consists of a thick sequence of sandstone that generally yields large quantities of good-quality water to wells. The aquifer is most important as a source of water supply in the Twin Cities area, where it supplies approximately 10 percent of the ground water used. It is the uppermost bedrock aquifer and, locally, the principal source of domestic supply where it is present north of the Twin Cities. Yield to wells are generally about 500 gallons per minute but may be as high as 2,000 gallons per minute. The aquifer is a good potential source of water because of (1) large quantities of water in storage, (2) adequate yields to wells, and (3) good water quality.

The quality of water in the aquifer is generally acceptable for municipal, industrial, and domestic uses. The dissolved-solids concentration in water from the aquifer ranges from a minimum of 48 milligrams per liter to a maximum of 2,810 milligrams per liter. The lowest values are in the eastern and northern parts of the aquifer, where bedrock is at or close to land surface. The highest concentrations are in the southwestern part of the aquifer, where leakage from over lying Cretaceous rocks is highly mineralized water. Magnesium and sulfate concentrations are also high in the southwest. The dissolved-solids concentration generally increases with depth in the aquifer. The predominant water type in the aquifer is calcium magnesium bicarbonate, although sodium chloride waters are present at depth and in the discharge areas along large rivers.

This report is one of a series of the hydrogeology and water quality of the 14 principal aquifers in Minnesota prepared by the U.S. Geological Survey. The U.S. Environmental Protection Agency requested these studies because of the need for information to develop its Underground Injection Control Program.