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• "3' Probable Hvdrologic Consequences of Minin The applicant has provided a discussion of the probable hydrologic consequences of the proposed mining operations on surface and ground water systems. This assessment, based upon mining in the D and E coal seams at a 50 to 55 percent recovery rate, is found in Section IV of the addendum (Kimball, et al., 1982). The proposed operation would undermine the Williams Creek and Ward Creek stream/alluvial aquifer system. The applicant has limited coal extraction beneath the valleys and no subsidence effects are expected. No major fractures have been identified in the permit area. The applicant has identified inflows to the mine (addendum, Map 6), and has not found significant inflows from the roof. In addition, the applicant's ground water investigations show no vertical communication between aquifers. Based on all of this information, no significant depletion of flow is expected to occur vertically through the strata overlying the underground workings. Some depletion of the stream/alluvial aquifer system could occur through the coal seams themselves with subcrop beneath the Williams Creek and Ward Creek valleys. Ground water movement in the permit area is updip, discharging to the stream/alluvial aquifer system. Mining will dewater adjacent portions of the coal seam aquifer and will intercept some of the ground water currently Discharging to the stream/alluvial aquifer system. In addition, the presence of the underground workings beneath the valley would reverse the existing ground water flow direction between the valley and the mine workings, and water from the stream/alluvial aquifer system would enter the mine workings through the coal seams. The applicant has provided a prediction of inflow to the mine flow the D and E coal seams on ayeariy basis. The maximum predicted inflow, 78.67 gpm (0.17 cfs) in 1983, provides an estimate of worst case streamflow depletion. (Since some of the ground water inflow comes from other sources, such as depletion of ground water storage, the actual stream flow depletion would probably be less than predicted.) The applicant estimated that two years after ground water removal begins, the total volume of water intercepted by the mine would be taken directly from the stream. The addendum reports that the minimum streamflow observed in Ward Creek by the ditch rider was 2.5 cfs in 1977. Therefore, the total mine inflow (and worst case streamflow depletion) represents only 7 percent of the lowest streamflow observed in Ward Creek. The predicted mine inflow is only about 2 percent of the average flow in Ward Creek. During operations, some of the mine water is returned to the Ward Creek drainage system. Mine water is pumped to a sediment pond, where water not lost to evaporeation is discharged to the Ward Creek system via