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-35- ~J ~J~ i; Other possible hydrologic impacts to surface water quality and quantity are not expected to be significant. Increased runoff and erosion from disturbed areas would be controlled by the applicant's runoff and sediment control system. The refuse pile should not have any adverse effects on the hydrologic system in the mine area or adjacent area. The applicant reached this conclusion about the impacts of the refuse pile for several reasons: 1) The pile is designed to reduce its permeability and a toe drain has been constructed to remove water from beneath the pile (minimizing the ground water build up in the pile); 2) The sides of the pile will be sloped, topsoiled, and revegetated to reduce the potential for water entering the pile and reducing erosion; and 3) Surface water from undisturbed areas will be diverted away from the pile. These factors, in combination with the limited amount of precipitation (14" annually) will tend to limit the amount of acidic, toxic and alkaline leachate generation. The only potential long-term effects are indirect surface water effects. The continued generation of leachate by the coal refuse pile, and the discharge of degraded ground waters from the mines to receiving streams may have a long-term effect on surface water quality, but they are not expected to be significant. The existing and proposed underground mine workings for the Eagle No.S and No. 9 mines are located beneath or adjacent to the Williams fork and Yampa River stream/alluvial systems. These mtne workings may intercept ground water currently discharging to the stream/alluvial system, and because of the reversal in ground water gradients, may actually divert water from the stream/alluvial systems to the underground workings. Flow from the stream/alluvial systems may reach the mines through several possible routes: 7) flow through the subcrops of affected aquifers into the mine workings; 2) Flow through fractures (natural or subsidence induced) into the mine workings;°and 3) Vertical flow through the intervening strata from the stream/alluvial systems to the underground workings (Normally, the third component may be considered negligible).