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perennial stream valleys, but under the steep hillslopes. The applicant has submitted analyses of the coals, roof, and floor strata. The analyses of the roof and floor materials performed by the Soils Laboratory of Colorado State University (Appendix 3-I) indicate that these units contain insufficient carbonate minerals to buffer the iron sulfide (e.g., pyrite) contained in these strata. These analyses indicate that these strata are acid-forming and potentially toxic. The inactive North Thompson Creek No. 2 Mine contains both acid and toxic mine waters (see laboratory analysis of Portal No. 2 Mine, dated June 22, 1982). This analysis shows that mine water in the No. 2 Mine exceeds receiving stream standards for the following ions: aluminum, cadmium, chloride, copper, iron, manganese, ammonia, sulfate, zinc, and total dissolved solids. A tield 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 is 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 l6