Available ground water in much of central Wisconsin is limited to discharge through wells of low yield. Aquifers that yield small amounts of water to wells include fractured crystalline rock at or near surface in the eastern part of the area, sandstone overlying crystalline rock in the southern and western parts, and glacial till that covers the area north and west of the Marshfield moraine. Many wells in crystalline rock yield less than 2 gpm (gallons per minute). About 90 percent of the wells in sandstone and most wells in glacial till yield 5-9.0 gpm. Outwash sand and gravel in segments of some bedrock channels, however, yield large supplies of water to wells. Wells in surficial sand and gravel in the lower valleys of major tributaries to the Wisconsin River yield as much as 450 gpm. Sand and gravel in segments of bedrock channels, many of which were delineated during this project, are covered by till or alluvium; wells in these sand and gravel deposits yield 100-400 gpm. Induced recharge to buried aquifers by infiltration of water through the beds of overlying streams is feasible at six sites within 8 miles of Marshfield. Infiltration through the streambed of Little Eau Pleine River about 7 miles northeast of Marshfield was about 200 gpm when the ground-water level was lowered temporarily. Additional recharge through ponding is possible at other sites. Streamflows in the area generally are not dependable sources of municipal or industrial supplies without storage. Nearly one-third of the flows measured in August 1969 were less than 0.01 cubic foot per second per square mile. Annual flows, however, would provide adequate within-year storage. Chemical quality of water in the area is suitable for most uses. Ground water is hard, contains objectionable concentrations of iron, and locally is high in nitrate content. Surface water has an average dissolved-solids content of about 100 milligrams per liter.
