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<br />GGG'? <br /> <br />formations not only makes them unsuitable for sources of water but <br />also unsuitable for use as possible recharge sites. The occurrence <br />of these deposits at shallow depths under lands served by the North <br />Sterling Irrigation District precludes recharge in this area. The <br />mantling deposits of dune sand and loess are not considered as aquifers <br />since these deposits generally lie above the water table and do not <br />yield significant quantities of water to wells. <br /> <br />Ground Water <br /> <br />Ground water in the alluvial aquifer occurs in an unconfined state, <br />Local ized confining and perching conditions may be observed due to <br />the presence of clay lenses. The water table slopes to the South <br />Platte River from both the north and south sides of the river. The <br />shape of the water table contours (Hurr, et al, 1975) indicate that <br />the South Platte River may be considered a gaining stream throughout <br />the study area. Depths to water range from less than 10 feet to about <br />100 feet and saturated thickness ranges from zero to over 240 feet. <br /> <br />The aquifer characteristics of interest are transmissivity, permeability, <br />and specific yield. Information regarding these parameters may be <br />found in USGS Water Supply Paper No. 1378 (1957) and in a series <br />published by the Water Resources Division of the Geological Survey <br />dealing with the hydrogeo10gic characteristics of the valley-fill <br />aquifer of the South Platte River Valley (Hurr and Schneider, 1972). <br />Transmissivities determined by pumping tests at six sites in the <br />alluvium ranged from 44,000 gallons per day per foot (gal/d/ft) to <br />290,000 gal/d/ft. Corresponding permeabilities varied from 490 gal/d/ft2 <br />to 3,160 gal/d/ft2 (65 ftlday to 42I ft/day). Based on the same <br />pumping tests, the storage coefficients (specific yield) ranged from <br />0.000082 to 0.179. <br /> <br />In the study area from Fort Morgan to the Colorado-Nebraska State line, <br />a potential storage capacity in excess of 900,000 acre-feet was calculated <br />for the unsaturated zone between the land surface and the water table. <br />This value is based on data obtained from the Geological Survey (1977, <br />unpublished report), It is estimated that this storage capacity is <br />high because of high water tables and the presence of clay and silt <br />occurring as layers and lenses. <br /> <br />39 <br />