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-35- <br />- subsidence-induced flows into the mines. <br />Faults and Fractures <br />Faults and fractures which cut the bedrock strata produce a localized increase <br />in porosity within the strata. If the faults and fractures do not become <br />sealed by clays, they may become conduits for the flow of ground and surface <br />water. When encountered within the mine, faults and fractures will dewater. <br />The amount of water flowing into the mine from these sources depends on <br />porosity and permeability of faults or fractures, and on the open vertical <br />connection within the faults and fractures between the coal seam and sources <br />of ground or surface water. <br />Fault and fracture controlled inflows have been noted and mapped in the U.S. <br />Steel Corporation Somerset Mine application (Exhibit E8-3366), the Western <br />Slope Carbon Hawk's Nest Mine permit application (Exhibit 2.04.7(1) or <br />W-1006), the Western Associated Coal Blue Ribbon Mine application (Exhibit T), <br />and the Colorado Westmoreland Inc. Orchard Valley Mine (Annual Hydrologic <br />Report dated December 30, 1982). No inflow mapping is available at present <br />for the Bear Mines. However, the company states that is it not presently <br />experiencing any mine inflows. The Mt. Gunnison No. 1 Mine has encountered <br />only minor inflows from fractures in the Number 1 portal. A quantitative <br />assessment of surface water depletion through mine inflows is contained in the <br />surface water section of the Cumulative Hydrologic Impact Study. <br />Dewatering of Coal, Roof, and Floor <br />From field observations made by CMLRD hydrologists in the mines and from <br />information contained in their respective permit applications, water was noted <br />to seep from the coal, roof, and floor upon advance of mining in the "B" and <br />"C" seams of the Somerset Mine, the "D" seam of the Orchard Valley Mine, the <br />"E" seam of the Hawk's Nest Mine and Blue Ribbon Mine, and "F" seam of the Mt. <br />Gunnison Mine. These sources of mine inflows dry up one to two weeks after <br />mining an area. The minor amount of water resulting from dewatering of the <br />coal, roof, and floor indicates that the coals and the overlying and <br />underlying strata in the Mesaverde Formation have very low permeabilities. <br />Thus, these strata store and transmit very little water and are not considered <br />aquifers. Therefore, the impacts of dewatering the coals and the strata <br />immediately above and below the coals within the Mesaverde Formation will have <br />an insignificant impact on the hydrologic balance. Also, the very slow rates <br />of inflow resulting from dewatering strata indicate that the quantity of water <br />transmitted by these strata will not result in depletion of surface water <br />sources. <br />SUBSIDENCE <br />Subsidence <br />The impacts of subsidence due to mining can be expected to vary in <br />magnitude and extent. This variation will result from a combination of <br />numerous natural phenomenon and from the effects induced by mining. <br />Surface water and ground water can both be influenced by differences in <br />