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How Chemicals Seep into the Aquifer

By Hank Becker
May 15, 1997

Scientists have answered one of the questions of the Midwest: how drinking water coming from aquifers gets contaminated with chemicals.

Walnut Creek, a tributary of the South Skunk River near Ames, Iowa, is a typical small stream in the area. Before flowing into the river, the creek passes over a sand and gravel aquifer.

Scientists with USDA’s Agricultural Research Service have confirmed the movement of water through the creek bed and into the underlying aquifer. They accomplish this by measuring water levels in the aquifer and flow in the stream on two sampling dates. Chemical analyses of 24 water samples showed that the water entering the aquifer contained nitrate and herbicides, including atrazine.

The scientists estimate that the creek could contribute substantially more atrazine to the aquifer than leaching through a field equal in area to that of the streambed.

Both the stream and aquifer conditions studied are common in the Corn Belt. Alluvial aquifers, sometimes called “buried valley aquifers,” are found near most major rivers in the region.

This type of aquifer has been found to contain the greatest contamination of all ground water resources in the Corn Belt. Defining the stream-aquifer connection could prove critical in explaining contamination of important ground water resources used by communities and farmers. Implications are that managing fields upstream may be more important than managing fields over an aquifer.

Scientific contact: Michael R. Burkart, ARS National Soil Tilth Laboratory, Ames, Iowa, phone (515) 294-5809, fax (515) 294-8125,