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Doc Date:1 2/1 112 0 01 III'lllll'lII1lI III <br />sss <br />• S/G Z.5 HYDAOLOOY <br />1.5.1 8IIIQ111RY 7-ND COHCLU9IOH9 <br />The proposed additions to the Edna Mine will be located in the Williams <br />Fork Formation and obtain coal from the Wadge seam. It is anticipated that <br />the hydrologic conditions that will be encountered in the proposed mine will <br />be very similar to those in the existing mine. <br />The mean annual precipitation on the study area is estimated to be 19.52 <br />inches. Approximately 2.69 inches of the precipitation are lost during the <br />winter months due to evaporation and sublimation. Of the remaining 16.83 <br />inches, evapotranspiration accounts for 14.73 inches, overland runoff for <br />another 0.15 inches, and the remaining 1.95 inches is subsurface runoff. <br />Runoff from the mine area enters Trout Creek that runs northward at the foot <br />of the slope. <br />Inflows to the pit on the down dip limit of mining in the West Ridge <br />area were estimated to be on the order of 65-125 gpm by D'Appolonia (1977). <br />• Inflows into the pit during the mining of West Ridge appeared to be less than <br />those predicted. Some wet spots were noticed along the low wall of the first <br />cut. However, this amount of inflow was insufficient to be quantified. Small <br />amounts of inflow to the pit from the upslope areas were encountered where <br />water from intercepted perched aquifers occurred, mainly in the existing <br />spoils. Inflows to the box cut on the Moffat Area were originally expected to <br />be 55-110 gpm. However, the orientation of the pit was altered from being <br />parallel with the hillslope to being perpendicular to the slope since the time <br />of the original estimate. Additionally, intercepted water from upslope areas <br />was estimated at about 10 gpm. Observations made since the opening of the <br />Moffat area have not noted any inflow from the downdip limit of mining and <br />only infrequent, small amounts of inflow have been noticed along the highwall <br />as perched aquifers have been intersected by the advancing pit. In the <br />absence of fractured permeability (as assumed in the above estimates), inflows <br />from the alluvium along Trout Creek to the pit in the West Ridge area should <br />have been less than 28 gpm based on the calculations in Section 2.5.3.1. The <br />corresponding value for the Moffat Area is anticipated to be less than 16 gpm. <br />Field observations regarding inflow into the pits indicate that the most <br />• reasonable estimate of flow from the alluvium to the pits is zero. <br />Mid-term '94 2.5-1 September 15, 1994 <br />