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-35- 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 Blue Ribbon Coal Company 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 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 surface water depletion through mine inflows is contained in the surface water section of the Cumulative Hydrologic Impact Study. Dewatering of Coal, Roof, and Floor From field observations made by CMLRD hydrologists in the mines 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 Mine and Blue Ribbon Mine, and "F" seam of the Mt. Gunnison 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 Mesa Verde Formation 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 Mesa Verde Formation will have an insignificant impact on the hydrologic balance. Also, the very slow rates of inflow resulting from dewatering strata indicate that the quantity of water transmitted by these strata will not result in depletion of surface water sources. Subsidence The impacts of subsidence due to mining can be expected to vary in magnitude dnd extent. This variation will result from a combination of numerous natural phenomenon and from the effects induced by mining. Surface water and ground water can both be influenced by differences in timing of mining and the physical environment. It is assumed that all mining will result in subsidence at some future point in time, although surface manifestation may require many years to occur. Therefore, control and predication of subsidence is critical, necessary measures to be implemented before and during any mining activity. Natural phenomena which influence subsidence are: - Depth of overburden; - Thickness of the coal seam; - Stratigraphy, lithology and structure of the overburden; and, - Topography