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Total inflows to each of the mines will average about 25 gpm. These predictions compare favorably with existing inflow conditions in the "E" seam mine. Distances downdip from the mine from which drawdowns will be noticeable are predicted to be 11.5 and 3.9 miles for the "D" and "E" seams, respectively. The results of the modeling suggest that the drawdown will not extend out to the glacial/alluvial aquifer through unfractured coals to the coal subcrops. Distances updip from mine workings from which drawdowns will be noticeable are predicted to be 44.6 feet and 5.8 feet for the "D" and "E" seams, respectively. A buffer zone of 200 feet will be maintained between mine workings and the subcrops. However, fractured coals could allow ground water movement from the glacial/alluvial aquifer to the mine workings. The implications of these effects to water users in the area are considered to be insignificant. No wells in the area to be affected by the drawdowns are completed solely in the "D" or "E" coal seams. In addition, the dip of the strata beneath the Grand Mesa to the north causes the coal seams to become deeper and more inaccessible downdip of the mine. At the farthest extent of the predicted drawdowns, the seams are several thousand feet deep. Therefore, the resultant impact produced by the mine's dewatering practices is considered to be insignificant. It should be noted that these predictions assume that significant subsidence or fault induced inflows do not occur. No major faults have been identified in the mine area. The applicant's limited coal extraction method is designed to prevent significant subsidence. Any subsidence effects are expected to be minor and easily reparable. Therefore, it is reasonable to assume that subsidence and faults will not cause significant inflow problems in the mine. Hydrologic monitoring will be required to verify this assumption (see Section VI - Ground Water of this document). There is also a potential for the water quality in the three aquifers to be impacted as a result of the proposed mining. This has already occurred in some of the old workings near the existing "E" seam mine. Water in these old workings has been found to have a TDS concentration of about 10,000 mg/l. This is extremely poor quality water. It is not known why the water quality in the old mine workings is so poor. However, it 1s possible that the water quality in the new mines will be equally as degraded when mining is completed. Once the coal seam aquifers are reestablished, (when the workings have filled with water after cessation of mining) discharge will probably again be to the glacial/alluvial aquifer through the coal seam subcrop. The applicant has calculated that the flow through the glacial/alluvial aquifer is about 1.53 cfs. Assuming that the discharge from the coal aquifers will be equal to the mine inflows, about 0.11 cfs will be discharging from the two coal seams into the glacial/alluvial aquifer. According to this scenario, the discharge from the two coal seams represents about IX of the total flow in the glacial/alluvial aquifer. A mass balance analysis conducted by the Division predicted that the resultant post-mining TDS concentrations in the glacial/alluvial aquifer would be about 900mg/1. The pre-mining TDS concentration in the aquifer averaged about 330 mg/l. This increase of 570 mg/1 is probably a worst case. The assumptions and variables used in the analysis are the same as those used by the applicant to predict post-mining water quality in Ward Creek (see page 68 of Volume 8 of the application, September 9, 1982, addendum). -26-