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manganese, ammonia, sulfate, zinc, and total dissolved solids. A field measurement of pH by DMG staff obtained a pH value of 2.5 for the No. 2 Mine water. It must be noted that this mine i5 abandoned and "pre-law"; it is not proposed to be reopened or permitted under this proposed decision. During mining, water that collects in the mine has limited exposure to the affected strata prior to discharge to the surface. Thus, there is little degradation of water quality. However, upon completion of mining, there is a potential for the formation of acidic and toxic mine waters. This degradation of water quality would result from the prolonged exposure of water to fractured roof strata and to the exposed coal and floor strata once the mine pumps are shut off. However, the water quality data for mine water discharges since the cessation of pumping at the North Thompson Creek Mines demonstrates that the discharge water has remained slightly alkaline. Elevated iron concentrations in the mine discharge water are treated before the water is discharged to North Thompson Creek. Ground water quality in overlying and underlying aquifers may become degraded upon closure of the mine through vertical communication of strata caused by faults and fractures. The overlying and underlying aquifers are currently not put to beneficial use and the potential for their future utilization is limited by the difficulty in developing water wells in these strata. Owing to these factors, the mines will not materially damage the ground water of any water user through vertical migration of degraded mine waters. The coal processing wastes from the wash plant are combustible, acid-forming, and potentially toxic. Owing to the.nature of these coal processing wastes, the coal refuse pile was constructed to minimize exposure of wastes to air, surface water, and ground water. The exposure to these wastes is being limited through (1> compacting the waste in two-foot lifts, (2> covering the refuse pile with one foot of non-toxic cover, (3) providing permanent surface diversion of surface runoff from undisturbed areas around the pile, (4) collecting and treating all surface drainage flowing over the pile during construction and reclamation, and (5> benching and sloping the pile such that erosion and infiltration of the final pile is minimized. The refuse pile was constructed on top of thin alluvium of the old stream channel which supplies drainage of ground water beneath the pile. The pile was constructed over the relatively impermeable Mancos Shale Formation and not over any aquifer. Therefore, the impacts of the refuse pile on the quality of ground water should be minimized and should not cause material damage to any ground water currently in use. _.5_