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-35- The permit and adjacent areas of the underground mines, have streams with steep gradients, steep slopes (average slope of 40%), and south facing slopes. All of these conditions favor runoff over infiltration. The downward migration of surface water to the mine workings is limited by the thickness of overburden and by the presence of impermeable and low permeable shales and siltstones. Given the nature and limited quantity of present mine inflows; the limited amount of infiltration of surface waters; and the geologic setting of the mine, there is very minor potential for future underground mining operations to cause interception of siynificant surface flows and diversion of the flows to the mine workings. The inflow waters which accumulate in the mine are used within the mine. The applicant has obtained a right to the use of the water from all mine inflows through a well permit, and also has adequate surface water rights to augment the inflow water use. The total mine inflows are insufficient to meet the dust suppression and cooling needs of the mines, thus the applicant has to import into the mine a majority of the water used in the mining operation. Since the inflow rates are minor, and since the applicant has a right to the inflow water, this impact of the mining operation on the quantity of surface water is minimal. The Hawk's IJest Mine consumes or recirculates most of the water introduced into the mine for the slurry backfilling of workings and for dust suppression and cooling. Thus the mine infrequently discharges mine waters to the surface. Most discharges have resulted from reopening of older workings in which water has accumulated over extended periods of time. These mine waters have been discharged in conformance with existing NPDES requirements. Therefore the impact of mine discharges on the quality of surface waters is minimal. Coarse coal refuse generated in the coal processing facility is Disposed of off-site near the Delta County Landfill at Hotchkiss. The impermeable Mancos Shale at this disposal site will prevent the movement of leachates into surface waters during and after construction, and will limit infiltration into the refuse pile after construction. The disposal is totally contained within a small (20 acre) drainage basin. The low average annual precipitation (less than 10 inches), small drainage basin and relatively flat topography are factors which minimize the potential for impacts to the surface water system. The disposal has been designed to prevent material damage to the quality and quantity of surface waters outside the permit area. CUMULATIVE HYDROLOGIC IMPACT ASSESSMENT acts on Ground Water The six underground mines along the North Fork of the Gunnison may impact ground water quantity by one or more of the following: