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Probable Hvdrolo4ic Consequences of the Red Canvon Mines Ground Water Potential impacts to the groundwater regime have been identified. During the active mining phase, mine pumping could cause drawdowns in the coal aquifers, extending several miles from the mine. Now that the mine is sealed three other impacts are likely to occur. Water in the flooded workings is likely to acquire a greater salinity and a more sodic character. This water may ultimately discharge to the glacial-alluvial aquifer at the coal subcrops and result in a degradation in water quality. Lastly, a spoil aquifer will develop in the underground waste disposal area and the backfilled areas of the reclaimed topography. Total projected inflows to each of the two Red Canyon mines will average about 25 gpm. Actual inflows in the "E" Mine averaged 25 gpm in 1983 and 1984. 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. There is also a potential for the water quality in the three aquifers to be impacted as a result of mining. This has already occurred in some of the old workings near the existing "E" seam mine. Water in these old workings has been monitored with a TDS concentration of about 10,500 mg/1 and an SAR of 27. This is extremely poor quality water. It is possible that the water quality in the new mines will be equally as degraded. -9-