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Surface Water <br />The mine is located ed~acent to Ennis Draw, a tributary to Box <br />Elder Creek which flows into the South Platte River near <br />Kersey, Colorado. There is no evidence of surface runoff in <br />the vicinity of the site. Essentially all precipitation <br />infiltrates the highly permeable mantle of sand. No <br />water-formed erosional features are evident, not even smell <br />rills or gullies. Ennis Draw is a broad, flat bottomed <br />depression with no observable channel or gully and shows no <br />evidence of the existence of surface flows. <br />4.5.4 Hydrologic Properties <br />Any possible effect of eah disposal on the subsurface waters <br />of Ennis Draw will be significantly reduced, as the area of <br />proposed ash disposal in A/B Pit will be above the mining <br />ground water table. <br />Instantaneous pit inflows from the Laramie Formation had been <br />expected to range from 20+ to 130 + gpm, depending upon the <br />number of pits open and duration since opening. (McWhorter, <br />1978). It was also estimated that piezometric drawdowns in <br />the Laramie Formation due to presence of the mine will be <br />extended no further than O.5 miles. The quality of <br />ground-waters after ash disposal is expected to be comparable <br />• to water resident in the Laramie shales and coals - no <br />appreciable degradation of water quality is anticipated as <br />Laramie ground-water passes through spoils or leaching through <br />ash enroute to the Ennis Draw subsurface water system. <br />Mine operations have remained 300' west of Ennis Draw. This <br />was based on recommendations presented in the hydrological <br />report relating the ability of ground-water to move through <br />the overburden. Mining operations have not disturbed <br />overburden materials (clays and clay shales) and therefore, <br />subsurface waters are confined and hindered from recharging <br />the eastern portion of the aah disposal area. <br />During the duration of mining in A-Pit since the opening of <br />the mine in 1980, minimal to non-existent pit inflows have <br />been encountered. The high estimates for pit inflow had been <br />based upon information at the time prior to mining. There <br />estimates were based on: <br />1. R high assumed saturated thickness of the overburden <br />2. The ability of the overburden to transmit water <br />3. The overall extent/presence of water in the overburden <br />u <br />-28- <br />