2019-05-29_REVISION - C1981018 (11)

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32 and drainage will tend to move down the dip of the mine and coal seam, thereby increasing the time to flood the workings. The permittee has proposed backfilling of the portals and construction of bulkheads upon closure of the mine, minimizing the possibility for discharge of water. A large coal refuse disposal area exists in the northern section of the mine permit area. Drill hole data indicate that there is no ground water within 44 feet of the ground surface in the disposal area, and recharge to ground water in the Mesaverde Group is minimal. Infiltration of water through the refuse pile will be minimized by covering the compacted refuse with 30 to 48 inches of the best available non-toxic material. Impacts to the ground water system are not expected to be significant due to the relatively impermeable nature of the refuse and the low water table. The development and reclamation of the cuts and fills in the portal areas should have no impact on the bedrock aquifer system. Recharge of the aquifers does not occur in these areas due to surface water control systems, so possible degradation of the ground water by infiltrating waters is unlikely. The fill material itself is generally of suitable quality as a topsoil substitute except for SAR values which are up to twice as high as defined in the Wyoming Guidelines for suitability. As water flows through the fill, total dissolved solids may increase due to soluble salts; however, this occurs naturally within the existing ground water region. The fill does not contain materials that create a toxic leachate. Water that infiltrates the fill may reach Scullion Gulch. However, due to the small area of disturbance relative to the entire drainage basin for Scullion Gulch, this will be a very minor contribution of flow in the creek. The permittee obtains part of the required water supply from the White River Lagoon, as discussed earlier. Approximately 552 ac. ft. per year (601 gpm is pumped from the lagoon to a head tank in the D-Portal area. This is less than one percent of the low flow of the White River. Therefore, impacts are not significant. Recharge of the ground water is not expected to be impacted significantly by the proposed mining operation. The majority of the recharge area for the Mesaverde aquifers is outside of the mine plan area. It is possible that surface fracturing resulting from subsidence could increase recharge to the Upper Williams Fork. However, these cracks, if they occur, are expected to exist for only a short period of time before naturally sealing. Recharge of the White River alluvium by bedrock aquifers is not considered to be significant because of the low transmissivities of the aquifers. The permittee has estimated that total discharge could be 1.3 gpm through bedrock aquifers to the White River, which is less than a tenth of a percent of the base flow of the river. Therefore, the expected change in the recharge capacity of the bedrock aquifers would not be a significant impact to the alluvial aquifer.