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-34- <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 />The impacts of subsidence due to mining can be expected to vary in magnitude <br />and extent. This variation will result from a combination of numerous natural <br />phenomenon and from the effects induced by underground mining. Surface water <br />and ground water can both be influenced by differences in timing of mining and <br />the physical environment. It is assumed that all mining will result in some <br />degree of subsidence at some future point in time, although surface <br />manifestation may require many years to occur. Therefore; control and <br />prediction of subsidence are critical, necessary measures, which should be <br />implemented before and during any mining activity. <br />Natural characteristics which influence subsidence are: <br />- Depth of overburden; <br />- Thickness of the coal seam; <br />- Stratigraphy, lithology and structure of the overburden; <br />- Topography; and <br />- Lithology of the floor strata. <br />Mining activities which affect subsidence are: <br />- Size, shape, depth, location, and areal extent of <br />workings; <br />- Rate of development and extraction of resource; and <br />- Mining methods. <br />The possible impacts of subsidence include: <br />- Modification of surface water hydrology - channel and watershed <br />geometry andsediment erosion rates; <br />I <br />