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Kansas Geological Survey, Public Information Circular (PIC) 2
Salt Contamination of Ground Water in South Central Kansas--Part 4 of 5

Predicting Saltwater Contamination

Many factors affect the nature, development, and predictability of natural salt contamination. Understanding the hydrology and geology of aquifers is important. Uncertainties in water use and management are caused by variations in the distribution of natural features (clay layers, faults, fractures, salt- and saltwater-bearing formations, ground-water flow patterns) and human-induced problems (improperly abandoned wells, bore holes).

Groundwater Management Districts 2 and 5 have established ground-water-quality monitoring networks and data bases to provide basic information to ground-water users. Additional information is available from other local, state, and federal agencies.

Pumping Wells in Areas Vulnerable to Saltwater Contamination

Pumping a well too hard can cause upconing of saltwater into the freshwater aquifer. Figure 3A illustrates a situation in which saltwater at the base of the freshwater aquifer does not rise much above the level of a partially confining clay layer. High-capacity wells in fig. 3B, however, create ground-water flow that pulls saltwater up through openings in the confining bed. Eventually, saltwater moves along the top of the clay layer and enters the well.

Figure 3A--The undisturbed aquifer contains saltwater at its base, but saltwater does not rise much above the level of the discontinuous clay layer.

Figure 3B--During pumping, saltwater moves toward the discharge points, and upconing beneath the pumping wells occurs.

High-capacity irrigation or municipal-supply wells have zones of influence that may extend more than a mile from the well. These wells can dramatically alter water-table elevations and ground-water- flow directions. Because ground water moves relatively slowly, it may take several years for an underground source of salt contamination to be diverted to the well or nearby wells. Once an area is contaminated, remediation by human modification is difficult, and natural processes are slow.

Severe drought can lead to salt-contamination problems not observed during normal or excess precipitation. During periods of little or no recharge, ground water continues to discharge naturally from freshwater aquifers, decreasing the thickness of the freshwater zone overlying the saltwater. Regional pumping is likely to be greater during droughts and can further decrease the thickness of the freshwater aquifer. Thus, upconing of saltwater can be more severe during extended droughts.

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Kansas Geological Survey, Geology Extension
1930 Constant Ave., Lawrence, KS 66047-3726
Phone: (785) 864-3965, Fax: (785) 864-5317

Web version Nov. 1995