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_ _.. Trinidad Sandstone <br />The Trinidad Sandstone, which immediately underlies the coal- <br />bearing strata, is a potentially developable aquifer throughout the <br />Park Plateau, but only a few wells on the eastern margin of the plateau <br />now draw upon it. Away from areas of outcrop the formation dips steeply, <br />and ground water conditions change from water-table to artesian. In <br />outcrop areas, the formation is drained, and wells must penetrate to <br />near the base of the formation where water is trapped by the underlying <br />Pierre Shale. The formation is saturated adjacent to streams, and <br />wells produce water at relatively shallow depths. <br />Wells in the formation yield small quantities of water (less than <br />5 gallons per minute with large drawdowns. The specific capacity <br />in a stock well in T33SR64WS22 is 0.004 gallons per minute per foot <br />• of drawdown. Mean laboratory permeabilities of core taken from well <br />USES 78-4 are: 5X10-4 ft/day, horizontal, and 3X10-4 ft/day, vertical <br />(Howard, in prepazation, p. 31). Pump and slug tests of USGS <br />exploration well in T33SR65WS35 indicate a transmissivity of 1.75 ft2/day <br />a hydraulic conductivity of 0.035 ft/day. <br />Ground water in six sampled wells by the U.S. Geological Survey <br />varies from sulfate to bicarbonate in composition. Calcium sulfate and <br />bicarbonate waters are generally low in dissolved solids (300-600 mg/L), <br />but two samples of sodium bicarbonate water are moderately to highly <br />mineralized (915 and 2,670 mg/L). <br /> <br />74 <br />