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-37- <br />- subsidence-induced flows into the mines. <br />Faults and Fractures <br />Faults and fractures which cut the bedrock strata produce a localized <br />increase in porosity within the strata. If the faults and fractures do <br />not become sealed by clays, they may become conduits for the flow of <br />ground and surface water. When encountered within the mine, faults and <br />fractures will dewater. The amount of water flowing into the mine from <br />these sources depends on porosity and permeability of faults or <br />fractures, and on the open vertical connection within the faults and <br />fractures between the coal seam and sources of ground or surface water. <br />Fault and fracture controlled inflows have been noted and mapped in the <br />U.S. Steel Corporation Somerset Mine application (Exhibit E8-3366), the <br />Western Slope Carbon Hawk's Nest Mine permit application (Exhibit <br />2.04.7(1) or W-1006), the Western Associated Coal Blue Ribbon Mine <br />application (Exhibit T), and the Colorado Westmoreland Inc. Orchard <br />Valley Mine (Annual Hydrologic Report dated December 30, 1982). No <br />inflow mapping is available at present for the Bear Mines. However, <br />the company states that is it not presently experiencing any mine <br />inflows. The Mt. Gunnison No. 1 Mine has encountered only minor <br />inflows from fractures in the Number 1 portal. A quantitative <br />assessment of surface water depletion through mine inflows is contained <br />in the 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 <br />from information contained in their respective permit applications, <br />water was noted to seep from the coal, roof, and floor upon advance of <br />mining in the "B" and "C" seams of the Somerset Mine, the "D" seam of <br />the Orchard Valley Mine, the "E" seam of the Hawk's Nest Mine and Blue <br />Ribbon Mine, and "F" seam of the Mt. Gunnison Mine. These sources of <br />mine inflows dry up one to two weeks after mining an area. The minor <br />amount of water resulting from dewatering of the coal, roof, and floor <br />indicates that the coals and the overlying and underlying strata in the <br />Mesaverde Formation have very low permeabilities. Thus, these strata <br />store and transmit very little water and are not considered aquifers. <br />Therefore, the impacts of dewatering the coals and the strata <br />immediately above and below the coals within the Mesaverde Formation <br />will have an insignificant impact on the hydrologic balance. Also, the <br />very slow rates of inflow resulting from dewatering strata indicate <br />that the quantity of water transmitted by these strata will not result <br />in depletion of surface water 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 />