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-33- The underground mining activites at the proposed Orchard Valley West mine site have been planned to minimizing disturbance of the prevailing hydrologic balance in both he disturbed area and adjacent area. Sediment and draiaage control measures will be performed in compliance with Rules 4.05.5 and 4.05.6. Impacts from mining to the surface water component of the East Roatcap Creek Drainage are expected to be minimal at best. The Overland Ditch which has previously been routed through East Roatcap Creek for conveyance to water right users below the proposed mine site will now be diverted to West Roatcap Creek. CUMULATIVE HYDROLOGIC IMPACT ASSESSMENT The proposed west portal facilities in East Roatcap Creek will not result in adverse hydrologic impacts as explained above, therefore, there will be no additional cumulative hydrologic impacts to the basin. Impacts 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: - induced inflows into the mines through faults and fractures which provide communication between the mine and overlying and underlying aquifers and surface waters; - dewatering of the coal, roof and floor with the advance of mining; and - subsidence-induced flows into the mines. 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 become sealed by clays, they may become conduits for the flow of ground and surface water. When encountered within the mine, faults and fractures will dewater. The amount of water flowing into the mine from these sources depends on porosity and permeability of faults or fractures, and on the open vertical connection within the faults and fractures between the coal seam and sources of ground or surface water. Fault and fracture controlled inflows have been noted and mapped in the U. S. Steel Corporation Somerset Mine application (Exhibit E8-3366), the Western Slope Carbon Hawk's Nest Mine permit application (Exhibit 2.04.7(1) or W-1006), the Western Associated Coal, Blue Ribbon Mine application (Exhibit T), and the Colorado Westmoreland Inc. Orchard Valley Mine (Annual Hydrologic Report dated December 30, 1982). The Bear Mine is it not presently experiencing any mine inflows. The Mt. Gunnison No. 1 Mine has encountered only minor inflows from fractures in the Number 1 portal. A quantitative assessment of su~face water depletion through mine inflows is contained in the surface water section of the Cumulative Hydrologic Impact Study.