Hydrology of the alluvial, buried channel, basal Pleistocene and Dakota aquifers in west-central Iowa

A ground-water resources investigation in west-central Iowa indicates that water is available from alluvial, buried channel, basal Pleistocene, and Dakota aquifers. The west-central Iowa area includes Audubon, Carrol1, Crawford, Greene, Guthrie, Harrison, Monona, and Shelby Counties.

Nine alluvial aquifers consisting of sand and gravel are in the valleys of the Little Sioux, Maple, Soldier, Boyer, West Nishnabotna, East Nishnabotna, South Raccoon, Middle Raccoon, and North Raccoon Rivers. These aquifers contain about 870,000 acre-feet of water that is potentially available to wells. Potential well yields generally are less than 50 gallons per minute. The water generally is very hard (greater than 180 milligrams per liter hardness as calcium carbonate), is a calcium bicarbonate type, and has an average dissolved-solids concentration of less than 600 milligrams per liter.

Seven buried channel aquifers Anthon, Denison, Fremont, Hardin Creek, Adaza, Beaver, and Bagley consisting of sand and gravel, underlie about 594 square miles in west-central Iowa and contain about 65,000 acre-feet of water potentially available to wells. Potential well yields of as much as 1,000 gallons per minute are possible in a few of the deeper and thicker parts of some of the buried channel aquifers, but well yields of 10 to 100 gallons per minute are more common. Water generally is very hard, is a calcium bicarbonate type, and has an average dissolved-solids concentration of 400 to 800 milligrams per liter in the shallow buried channel aquifers in Carrol1, Greene, and Guthrie Counties. In the deep buried channel aquifer in Audubon, Crawford, Harrison, Monona, and Shelby counties, the water generally is very hard, is a sodium sulfate or calcium sulfate type, and has an average dissolved-solids concentrations of 3,000 milligrams per liter.

The basal Pleistocene aquifer is at the base of the Pleistocene deposits on many bedrock ridges and consists of sand and gravel. Estimated well yields of as much as 500 gallons per minute can be obtained from the aquifer; however, 5 to 50 gallons per minute are more common. Water from the basal Pleistocene aquifer generally is very hard, is a calcium bicarbonate or calcium sulfate type, and has an average dissolved-solids concentration of 1,000 milligrams per liter.

The Dakota aquifer consists of the saturated sandstone and gravel units in the Dakota Formation. Isolated erosional remnants of the Dakota Formation form the caps of many bedrock ridges. The Dakota Formation is thickest where the bedrock surface is relatively high and flat, forming an ancient, buried, surface-water divide between southwest and southeast trending buried drainages in Audubon, Carroll, and Guthrie Counties. Sandstone thickness of as much as 150 feet exists in Guthrie County, but an average thickness of 30 feet is more common. Water from wells less than 200 feet deep generally is a calcium bicarbonate type and has an average dissolved-solids concentration of 650 milligrams per liter. Water from wells more than 200 feet deep generally is a calcium sulfate or sodium bicarbonate type and has an average dissolved-solids concentrations of 2,200 milligrams per liter.