Availability and Chemical Quality of Water From Surficial Aquifers in Southwest Minnesota

The principal surficial aquifers in southwest Minnesota are composed of outwash and alluvial material 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 in the valleys of the tributaries to the major streams yield small water supplies that are adequate for farm use. The surficial aquifers range in width from 0.5 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 thick as 15 feet, has been deposited over the outwash by post-glacial 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 313 to 958 milligrams per liter. Analyses of 25 samples show that the water locally contains concentrations of iron, sulfate, and nitrate that are above the limits recommended by the Minnesota Department of Health for drinking water. Based on these standards, the water is generally of acceptable chemical quality for most uses, although it is hard.