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Alluvium <br />The alluvium is in contact with the coal and Middle Sandstone for <br />only a small portion of the length of the mine. However, CfiC made a <br />worst-case estimate of stream depletion through the alluvium, <br />assuming the units are in contact along the length of the mine. The <br />worst-case stream depletion estimate is 182 gpm. <br />Predicted Mine Inflows <br />Ground water inflow analyses were performed on the No. 5 Mine inflow, <br />(Empire Energy, 1983). An additional analysis was also performed on the 2 <br />West Mine inflow in the No. 5 Mine. The projected mints inflows were made <br />assuming an aggressive mining sequence in both mines with completion of all <br />mains in the No. 5 Mine in 1984. A less aggressive miming sequence would <br />produce smaller maximum inflows for the mines. This prediction was subse- <br />quently altered to take into account longwall mining artd the acquisition of <br />additional land (Empire Energy, 1984). <br />Hydrologic properties of the coal were estimated by borrowing data on the <br />coal beds at the nearby Northern Coal Mine and verified by back-calculation <br />using measured inflows to the No. 9 Mine and McWhorter's (1981) method for <br />calculating inflow to mines from a coal seam. The same aquifer properties <br />were assumed to apply to the coal in the No. 5 and No. 6 Mines. <br />Because the McWhorter method ie not well suited for application to longwall <br />mining scenarios, inflow to the No. 6 Mine was estimated using the Jacob- <br />Lohman constant drawdown equation and the Thiem steady state equation. <br />Inflows to the No. 5 Mine were estimated using the Jacob-Lohman method. <br />Details of the calculations are presented in the PHC section of the permit <br />application package. <br />The results of the inflow calculations are summarized i~a Permit Table 75 <br />and 76 of the permit application package. The two methods used to predict <br />mine inflows produced similar values. They both predict the highest inflow <br />to occur after year five of mining and to range from 1,:300 to 1,800 gpm <br />combined inflow from the No. 5 and No. 6 Mines. To be conservative, the <br />highest seepage inflow value for the No. 6 Mine was seltacted as the <br />prediction to be used in the estimate of the maximum probable inflow. This <br />value, 700 gpm in year 20, was doubled to take into account the <br />unpredictable hydrologic conditions.. Only the .inflow from, the No. 6 Mine <br />~~~ north of~~the~No. 5 Mine was doubled. The inflow from ttte No. 5 Mine has <br />been fairly constant for a number of years and additionatl inflows are not <br />expected. No additional inflow should occur in the portion of the No. 6 <br />Mine that is under the No. 5 Mine, ae no faults were encountered in the <br />overlying mine. The total worst-case maximum combined inflow is estimated <br />to be 2,490 gpm. <br />21 <br />