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-34- Dewatering of Coal, Roof, and Floor Water often enters a mine in a newly opened area by dewatering the coal seam, adjacent roof or floor. These sources of mine inflow usually dry up within one to two weeks. Field observations made by CMLRD hydrologists in the mines and from information contained in operators' respective permit applications, document water seeping 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. 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 permeabiliti.es. Thus, these strata store and transmit very little water and are not considered to be aquifers. Therefore, the impacts of dewatering the coals and the strata immediately above and below the coals within the Mesa Yerde 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 ground water sources. IMPACTS ON SURFACE HATERS The Division, based on review of the permit applications for the mining operations considered in this assessment, has identified several possible effects of mining on surface water quality and quantity (Table 6). Disturbed areas will generate an increase in suspended solids in the area. Surface water quality might be affected by the discharge of mine water from underground workings or by seepage from waste rock or coal refuse piles to the stream - alluvial aquifer system. The underground mining operations, through subsidence effects may reduce stream flows or flows from springs and seeps. Future mining in the Minnesota Creek drainage basin may result in flow reductions to springs and streams associated with alluvial valley floors. This will result in the need to develop augmentation plans to protect holders of water rights. The withdrawal of surface water for mine usage may deplete surface flows. Lastly, the discharge of poor quality water from flooded underground workings could be a long-term impact. The likelihood and relative importance of these impacts are described in greater detail below. Runoff From Disturbed Areas Surface flow from disturbed areas would carry higher sediment concentrations than natural runoff. However, Rule 4.05.2 requires that all disturbed flow pass through a properly designed sediment control pond. Effluent from the pond is required to meet NPDES limitations prior to discharge. During operation, monitoring and inspection by the Division ensures that the sediment control system is maintained to function as designed. At the close of operations, surface disturbances would be reclaimed and the sediment control system would be removed following the ensuing liability period. Asa result, the increased sediment load carried by disturbed flows would not be expected to reach receiving streams.