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<br />I <br />I <br />I <br /> <br />Lake Andes stores water only during periods of high runoff and would not <br /> <br /> <br />provide an adequate water supply for the project. Between 1924 and 1975, <br /> <br />the lake, on the average, was dry 1 year out of every 20. Between 1975 and <br /> <br /> <br />1982, Lake Andes was dry. Due to extremely wet springs in 1983 and 1984, <br /> <br /> <br />the north remnant peaked at elevation 1439.4, middle remnant at 1437.4, and <br /> <br />south remnant at 1433.8 in June 1984. <br /> <br />I <br /> <br />I <br /> <br />Available data from 1964-69 and 1983-84 indicate that water quality in the <br /> <br /> <br />lake is highly variable--TDS value, vary between 550 and 6,400 mg/l; major <br /> <br /> <br />constituents are generally calcium and sulfate. <br /> <br />I <br />I <br />I <br />I <br /> <br />Both Choteau Creek and Lake Andes will receive project return flows. The <br /> <br />sampling program initiated in 1983 will aid in analyzing their ability to <br /> <br /> <br />assimilate return flows. This pro~ram and a degradation investigation of <br /> <br /> <br />Choteau Creek channel are addressed in more detail in the Water Quantity <br /> <br /> <br />and Quality section in Chapter 5. <br /> <br />I <br />I <br />I <br />I <br />I <br /> <br />Choteau Aquifer.--Choteau Aquifer underlies most of the Lake Andes-Wagner <br /> <br /> <br />Unit. The only data available for this aquifer is South Dakota Geological <br /> <br /> <br />Survey Bulletin 22, "Geology and Wllter Resources of Charles Mix and Douglas <br /> <br /> <br />Counties, South Dakota." This bulletin shows that the aquifer stores up to <br /> <br /> <br />2,000,000 acre-feet. Extensive test wells would be required to determine <br /> <br /> <br />the aquifer yield. Present wells in the area indicate a yield of about 400 <br /> <br /> <br />to 1,000 gal/min. <br /> <br />I <br /> <br />It is known that the water quality from the aquifer is poor compared to <br />Missouri River water. The average TDS is about 1,700 mg/l and the average <br />SAR is 8.5. Due to the poor quality and questionable quantity of the <br />aquifer water as compared to the good quality and quantity of Missouri <br />River water, development of the aquifer was not considered further. <br /> <br />I <br />I <br />I <br />I <br /> <br />~ <br /> <br />Soils and Topography <br /> <br />The Lake Andes-Wagner Unit lies on a till plain formed over a buried <br /> <br /> <br />preglacial valley. The stone-free ,i1ty surface soils suggest that the <br /> <br />9 <br />