1992-07-22_GENERAL DOCUMENTS - C1981017

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-38- The three underground mines along the Roaring Fork River 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 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 between the coal seam and sources of ground or surface water. Fault and fracture controlled inflows have been noted and mapped in the Snowmass Coal Company North Thompson Creek Mines application (Figure 3.6.1-5 to -7), 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 Blue Ribbon Coal Company, Blue Ribbon Mine application (Exhibit T) and the Colorado Westmoreland, Orchard Valley Mine (Revision Submittal of November 18, 1982). The Mt. Gunnison No. 1 Mine has encountered only minor inflows from fractures in the No. 1 portal . From field observations made by CMLRD hydrologists in the mines in the adjacent Somerset Coal Field and from information contained in their respective permit applications, water was noted to seep from the coal , roof, and floor upon advance of mining in the "B" and "C" seams of the Somerset Mine, the "D" seam of the Orchard Valley Mine, the "E" seam of the Hawk's Nest and Blue Ribbon mines, and "F" seam of the Mt. Gunnison No. 1 Mine. These sources of mine inflows dry up one to two weeks after mining an area. The minor amount of water resulting from dewatering of the coal , roof, and floor indicates that the coals and the overlying and underlying strata in the Mesaverde Group have very low permeabilities. Thus, these strata store and transmit very little water and are not considered aquifers. Therefore, the impacts of dewatering the coals and the strata immediately above and below the coals within the Mesaverde Group will have an insignificant impact on the hydrologic balance. Also, the very slow rates of inflow resulting from dewatering strata indicated that these strata will not transmit significant quantities of water which would result in depletion of surface water sources.