of Underground Water
Text by Jean Cutler Prior
Photo by Roger A. Hill
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.
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.
Adapted from Iowa
Geology 1997, Iowa Department of