Laserfiche WebLink
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 with possible development of tension cracks on the surface due to <br />differential settling. Observed ground water inflows during mining have <br />been approximately 50 gpm. In fractured areas, increased flows of 100 to <br />300 gpm may be encountered for a short period of time. These flows will <br />diminish as equilibrium is reestablished. Due to the low transmissivities of <br />the aquifers, if caving should create a hydrologic connection from the mine to <br />an aquifer within 30 to 40 feet of the coal, the additional inflow will be <br />minimal. It is not probable that fracturing from the mine to the surface will <br />occur as a result of subsidence and cause the flow of surface water to the <br />mine. <br />Subsequent to completion of mining, the ground water will slowly reestablish <br />its pre-mining water levels. Due to caving of the roof materials into the <br />mine, an area of increased permeability will exist within the mine that 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 Pack 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 />minimal. <br />The possibility exists for water to discharge from the portals once the mine <br />workings have become completely flooded. The portals are up-dip in the <br />mine, and drainage will tend to move down dip of the mine and coal seam, <br />thereby increasing the time to flood the mine workings. The permittee has <br />proposed backfilling of the portals and construction of bulkheads upon <br />closure of the mine, minimizing the possibility for discharge. <br />A large coal refuse disposal area exists in the northern section of the mine <br />permit area. Drillhole data indicate that there is no ground water within 44 <br />feet of the ground surface in the coal refuse disposal area, and recharge to <br />ground water in the Mesaverde Group is minimal. Infiltration of water <br />through the refuse piles will be minimized by covering the compacted refuse <br />with 30 inches of the best available nontoxic material. Impacts to the ground <br />water system are not expected to be significant due to the relatively <br />impermeable nature of the 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, <br />which makes possible degradation of the ground water by infiltrating waters <br />is unlikely. The fill material itself is generally of suitable quality as a topsoil <br />substitute except for SAR values which are up to twice as high as defined in <br />the Wyoming Guidelines for suitability. As water flows through the fill, total <br />dissolved solids may increase due to soluble salts; however, this occurs <br />naturally within the existing ground water region. The fill does not contain <br />Deserado Mine 35 June 18, 2009