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-32- The underground mining activities at the proposed Orchard Valley West mine site have been planned to minimize disturbance of the prevailing hydrologic balance in both the disturbed area and adjacent area. Sediment and drainage control measures are performed in compliance with Rules 4.05.5 and 4.05.6. Subsidence impact mitigation will result in short-term impacts as runoff from affected lands in the surface water area does not contribute measurably to stream base flow in the summer months. The mine plan has been developed to minimize undermining of streams. The applicant has adequate water rights to mitigate any mining-related impacts which would occur. CUMULATIVE HYDROLOGIC IMPACT ASSESSMENT DESCRIPTION OF GROUND WATER STUDY AREA The ground water system in the Paonia and Somerset area is divided by the North Fork of the Gunnison River into two separate systems. The strata in the general area dip shallowly in a northerly direction. The North Fork of the Gunnison River canyon isolates the coal beds and aquifers of the Mesa Yerde group north and south of the river. The ground water systems on either side of the river are isolated from each other will only be impacted by mines on one side of the valley. The mines north of the North Fork of the Gunnison River are Hawk's Nest, Somerset, Blue Ribbon, and Orchard Valley. The Terror Creek Loadout is also on the north side of the river. Mines south of the river include Mt. Gunnison, Bear Mines 1, 2, and 3, and the Hawk's Nest Landfill. IMPACTS ON GROUND WATER The six underground mines and one loadout along the North Fork of the Gunnison may impact ground water quantity by one or more of the following: inflows into the mines through faults and fractures which provide communication between the mine and overlying and underlying aquifers and surface waters; subsidence-induced flows into the mines; and dewatering of the coal, roof and floor with the advance of mining. The Mesa Verde formation is a very poor regional aquifer, and consequently, vertical permeability results in greater water flows than flow from horizontal transmissivity. Therefore, discussion of ground water impacts will be focussed on natural and induced fractures. Faults and Fractures Faults and fractures which cut the bedrock strata produce a localized increase in porosity within the strata. If the faults and fractures do not became sealed by clays, they may bec a conduits for the flow of ground and surface water. When encountered withi the mine, faults and fractures will dewater. The amount of water flowing in ,o the mine from these sources depends on porosity and permeability of faults or fractures, and on the open vertical