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News Release, Kansas Geological Survey, Nov. 23, 1998

KGS Releases Report on Water Potential from the Dakota Aquifer

LAWRENCE--With declines in the groundwater levels in the Ogallala Formation in western Kansas, water users have begun looking deeper for potential water sources.

One possibility, the Dakota aquifer, is the subject a new, semi-technical book available from the Kansas Geological Survey, based at the University of Kansas.

The Dakota is no replacement for the Ogallala, concludes Allen Macfarlane, Survey water specialist and one of the authors of the report. Unlike the Ogallala, the Dakota cannot produce large amounts of high-quality water. But with careful management, the Dakota can be a significant water source in some parts of the state.

"The Dakota aquifer has been used for water for more than a century in Kansas," said Macfarlane. "But it was poorly understood. Before this study, relatively little was known about the quantity or quality of water in the Dakota."

The Dakota aquifer consists of several rock layers that were deposited during the Cretaceous Period of geologic history, about 80 million years ago. The Dakota lies beneath the much younger Ogallala Formation, which was deposited during the past several million years.

Kansans probably know Dakota rocks best from the places they appear at the surface. Orange and red sandstones that crop out in Ellsworth County in central Kansas, for example, are part of the Dakota. Rocks that make up the Dakota aquifer are also found underground, beneath roughly the western half of Kansas, west of a line from about Comanche County in the south to Washington County in the north.

In the subsurface, water is sometimes found in pore spaces between the grains of sand in the sandstone layers in the Dakota aquifer. Where the Dakota consists of sandstone, it generally produces more water. Where it consists of other rocks with smaller pore spaces, such as clays or shales, it produces little or no water. Thus, knowing the composition of the Dakota aquifer is important in understanding its ability to produce water.

"Even over distances of only a few miles, the amount of sandstone in the aquifer can vary dramatically," said Macfarlane. "That affects the amount of water that it can produce."

In some parts of western Kansas, such as Ford and Hodgeman counties, wells in the Dakota can produce as much as 1000 gallons of water per minute. However, most wells in the Dakota produce considerably smaller amounts of water.

The quality of Dakota water can also be a problem. In parts of the aquifer, the water is naturally high in salinity. That naturally salty water has moved up from older rocks that lie beneath the Dakota.

In general, the Survey's study shows that the highest quality water from the Dakota is found in southwest and parts of central Kansas.

"In parts of north-central and northwestern Kansas, Dakota water is far too salty for most uses," said Macfarlane. "Because the salinity in the water generally increases with depth in the Dakota, the best quality water is usually found at the top of the aquifer."

Macfarlane's study has made it clear that the Dakota is an important water source, but it does not contain nearly as much extremely pure water as the overlying Ogallala Formation. As a result, he points out, using the Dakota will require careful management, such as spacing wells far enough apart to avoid significant water-level declines or pumping at levels that will pull up poorer-quality water.

"The Dakota should not be considered a replacement for the Ogallala Formation," said Macfarlane. "But if it is managed properly, it will be an important source of water well into the future."

The report, User's Guide to the Dakota Aquifer in Kansas, by Macfarlane, John Doveton, and Donald Whittemore, is available from the Kansas Geological Survey, 1930 Constant Ave., Lawrence, KS 66047 (or phone 785-864-3965). The cost is $10 per copy, plus $3 postage and handling. Kansas residents should add 6.9% sales tax.

For more information on the Dakota aquifer, see the Dakota Aquifer Program web site.
A short extract from this publication is available.

Story by Rex Buchanan, (785) 864-3965

Kansas Geological Survey, Publications and Public Affairs