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Subsidence effects include fracturing of the material overlying the coal for a <br />distance of 30 to 40 feet due to caving of the roof material and surface <br />subsidence and possible development of tension cracks on the surface due to <br />differential settling. Observed ground water inflows during mining have been <br />approximately SO gpm. In fractured areas, increased flows of 100 to 300 gpm <br />may be encountered for a short period of time. These flows will diminish as <br />equilibrium is reestablished. Due to the low transmissivities of the aquifers, <br />if caving should create a hydraulic connection from the mine to an aquifer <br />within 30 to 40 feet of the coal, the additional inflow will be minimal. It is <br />not probable that fracturing from the mine to the surface will occur as a result <br />of subsidence and cause the flow of surface water to the mine. <br />Subsequent to completion of mining, the ground water will slowly reestablish <br />its pre-mining water levels. Due to the caving of the roof materials into [he <br />mine, an area of increased permeability will exist within the mine which will <br />act as a "sump area" until equilibrium is established. However, due to the <br />small quantity of water in the aquifers being discharged to the White River <br />and its tributaries, the lack of ground water usage in the area, and the poor <br />quality of ground water, potential impacts to flow in the White River will be <br />very minor. <br />It could be possible for water to discharge from the portals once the mine <br />workings have become completely flooded. The portals are updip in the mine <br />and drainage will tend to move down the dip of the mine and coal seam, <br />thereby' creasing the time to flood the workings; however, it is uncertain if <br />the dfainage out of the mine area through the coal seam will exceed the <br />drainage into the mine from overlying strata. If outflow does not exceed <br />inflow, some discharge from the portals may occur. The permittee has <br />proposed bacld-illing of the portals and construction of bulkheads upon closure <br />of the mine, minimizing the possibility for discharge of water. / <br />In the-noRheut-sestie.~f-ii~~mine-plaerarea-is-a-targe-c~refuse disposal <br />area. Drill hole data indicate that there is no ground water within 44 feet of <br />the ground surface in the disposal area, and recharge to ground water in the <br />Mesaverde Group is minimal. Infiltration of water through the refuse pile <br />will be minimized by covering the compacted refuse with four feet of the best <br />available non-toxic material. Impacts to the ground water system are not <br />expected to be significant due to the relatively impermeable nature of the <br />refuse and the low water table. <br />The development and reclamation of the cuts and fills in the portal areas <br />should have no impact on the bedrock aquifer system. Recharge of the <br />aquifers does not occur in these areas due to surface water control systems, so <br />possible degradation of the ground water by infiltrating waters is unlikely. <br />The fill material itself is generally of suitable quality as a topsoil substitute <br />except for SAR values which are up to twice as high as defined in the <br />Wyoming Guidelines for suitability. As water flows through the fill, total <br />17 <br />