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Twentymile Coal, LLC (TC) <br />Narrative <br />Lease by Modification Application Wolf Creek Reserve — April 2014 <br />Potential Mining -Related Impacts on Surface Water Quantity and Quality <br />The planned underground mining activities have the potential of creating changes in surface <br />water quantity in terms of runoff volumes, flow rates, and direction and location of surface <br />water drainage. Potential impact mechanisms include: <br />1) Changes in runoff and recharge due to surface subsidence <br />2) Diversion of overland flow with ditches <br />3) Detention of surface runoff in sedimentation ponds and related evaporation losses <br />4) Discharge of mine inflows to surface water drainages <br />5) Induced recharge or discharge by underground mine dewatering <br />Changes in surface topography could affect surface water runoff and infiltration, <br />Subsidence -related changes in the surface topography will, however, be minor (on the order <br />of 3 to 6 feet), and will not result in changes in either topography or slope that would <br />significantly influence runoff or infiltration. Where differential (trough) subsidence occurs, <br />minor ponding and increased infiltration may result, however, heavy runoff from spring <br />snowmelt will result in increased siltation and filling of any low areas, gradually eliminating <br />ponding and restoring a stable balance of runoff and infiltration. <br />It is not anticipated that any significant diversions will be necessary in the Wolf Creek <br />mining area. The possibility exists of constructing short collection/diversion ditches to <br />control drainage for the limited surface facilities (shafts, dewatering installation, and <br />ancillary facilities) that could be required in the future to support mining operations, <br />however, the use of alternative sediment controls is more likely, and any ditches constructed <br />would control very small contributing drainage areas. Detention of surface runoff in <br />sedimentation ponds can decrease peak flow rates and reduce the amount of water available <br />downstream. It is not currently anticipated that sediment pond construction would be <br />required for the planned Wolf Creek mining operations. <br />In general, mine water requirements dictate that all mine inflow water be recycled, with no <br />discharge to surface drainages. At present, mine inflow water flows to in -mine sumps and is <br />transferred to sealed and abandoned mine workings for temporary storage. From the <br />underground storage reservoirs, water can be routed to the mine water system for in -mine use <br />(primarily equipment cooling and dust control) or can be pumped to the surface for use in <br />TC's coal processing facilities. While TC has a permitted NPDES discharge point for mine <br />water on Fish Creek upstream from the Wolf Creek mining area, it has only been utilized on <br />a limited basis in recent years. Given overburden depth and the presence of relatively thick <br />low -permeability shales in the geologic sequence between the mineable coal seam and the <br />surface, mining and associated dewatering have little or no influence on surface drainage and <br />flows. <br />The quality of surface and ground water could possibly be affected by water handling and <br />treatment methods under the planned operations of the Foidel Creek Mine. Impacts of <br />WCR BLM Lease App Narrative 0414.docx Page 13 <br />