Kansas Geological Survey, Open-file Report 1981-7
Carl D. McElwee and Munir Butt
KGS Open File Report 1981-7
Prepared for the U.S. Army Corps of Engineers
When the original report, "A Study of the Salt-Water Intrusion Problem Between Salina, Kansas, and Solomon, Kansas, in the Smoky Hill River Valley," was completed as originally planned, several additional points had come to light and needed additional research. This addendum addresses those points we felt most deserving of additional research.
The following points are with regard to the Wellington aquifer model. Improved valley wall definition did not significantly change the results of the original report. The volume reductions of salt-water leakage are still in the 20% range. Regional flow can capture about 50% of the fresh-water leakage induced by the relief wells in some cases. The result is that the water discharged in the natural discharge zone is considerably diluted. The net effect of the relief well system may be a reduction of 70-80% in the salt load discharged to the alluvium. However, studies of the time scale for the dilution to occur indicates that 50-150 years may elapse before most of the dilution effect is felt at the discharge area.
We have also considered several factors affecting chemical quality of the water pumped during a Wellington aquifer pump test. The fresh-water leakage induced by pumping could dilute the pumped water and lower the concentrations of various constituents. We have considered the time for water to move through the confining layer, leakage as a function of radial distance, travel time as a function of radial distance, and the effect of regional flow. The conclusion is that for the typical pumping test lasting only a few weeks no significant change in chemical quality should be observed.
The following comments are with regard to the effectiveness of a bank-side alluvial relief well system. First of all, we estimated the effect on a single rather small flood event. we found that pumping at or double the estimated bedrock flux value would not prevent upconing after the flood peak; however, it did reduce the intrusion to the river considerably. Pumping at double the bedrock flux rate would cause the salt-water mound under the river to decay.
Similar results were found with a more detailed model that tried to take into account a series of flood events. The pumpage from the bank-side alluvial relief well system could not always prevent upconing following a sizeable flood event at pumpage rates equal to or double the estimated bedrock flux. However, the relief well system did lower the peaks in the chloride concentration considerably.
Lastly, a series of hypothetical management schemes were tested to try to control the chloride concentration. The net result was that, if concentrated brine could be withdrawn from the alluvium and placed in either a reservoir or the river at the appropriate time, the river chloride concentration could be maintained at or below 250 mg/l. However, there are several practical problems that would prevent the complete accomplishment of this feat.
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Kansas Geological Survey, Geohydrology
Placed online Dec. 27, 2010
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