The principal surficial aquifers in southwest Minnesota consist of outwash and alluvium material deposited in river valleys. The largest and most productive of these aquifers occupy the valleys of the Cottonwood, Des Moines, Redwood, and Rock Rivers and of tributaries to the Big Sioux River. Minor aquifers, adequate only for farm or domestic use, occur in the valleys of tributaries to the major streams. The surficial aquifers range in width from half a mile to 2 miles, in thickness from 0 to 110 feet, and in saturated thickness from 0 to 80 feet. Grain size varies both laterally and vertically. A veneer of fine-grained sediment, as much as 15 feet thick, has been deposited over the outwash by postglacial streams. Availability of water in the surficial aquifers varies greatly within short distances. Probable maximum well yield is as much as 1,000 gallons per minute; however, yields generally range from 10 to 100 gallons per minute. The concentration of dissolved solids in water from the surficial aquifers ranges from about 300 to 960 milligrams per liter. Analyses of 25 samples show that locally the water contains concentrations of iron, sulfate, and nitrate (as nitrogen) that are above the limits recommended by the Minnesota Department of Health for drinking water. Based on these standards, the water is of acceptable chemical quality for most uses, although it is hard. (USGS)
