Water takes many recognizable forms on the land surface. Its movement, behavior, and uses are fairly familiar. As water seeps below the land surface, however, it becomes a more mysterious subject.
Though the ground generally is regarded as being “solid,” underground water pumped by wells flows through the kitchen faucets of over 80 percent of Iowa homes. It is a myth that this water is stored in large underground rivers and lakes.
It is the openings within earth materials – their abundance, size and interconnectedness – that determine what happens to water below ground. In sand, gravel or sandstone, spaces between the grains store groundwater. In limestone and dolomite, these openings are actually fractures, from hairline to cavern-size. Groundwater can move freely through all these materials. Clay and shale have the opposite effect. The tiny pores in these tightly packed materials may hold water, but it cannot easily pass through. Water
movement underground is further affected by the slope of water-bearing earth materials and whether they are confined by dense overlying materials or are under the influence of a nearby pumping well.
Water ponds on a farm field in Iowa. Photo by David Morris
To find Iowa’s vital but concealed underground water resources, and safeguard their drinking quality, we need to know how water-bearing materials (called aquifers) are distributed beneath the state – their depth, thickness, extent and the details of their composition as well as the earth materials above and below them. Ongoing research to improve the accuracy of this geologic information will give Iowans the information they need to locate wells and protect water supplies from contamination now and in years to come.
By Jean Cutler Prior
Adapted from Iowa Geology 1997, Iowa Department of Natural Resources
Iowa Geological Survey
The University of Iowa
300 Trowbridge Hall
Iowa City, Iowa 52242-1585