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downstream water sampling to determine acceptable discharge rates to maintain the sulfate levels <br />below the 250 mgQ in-stream standazd. This standazd applies year-round to this reach due to drinking <br />water usage. Modeling indicates conductivity (964 umhos/cm and SAR 2.4 highest modeled) should <br />not be a problem. <br />Yampa River -Below Trout Creek-Increases in both TDS and sulfate will occur in the Yampa River <br />due to mine water discharges. The applicant predicts an increase in both dissolved solids and sulfate <br />of approximately 9% over ambient levels. This increase would not affect any current uses or exceed <br />the in-stream standards. <br />Detention of surface water runoff in sedimentation ponds and related evaporation loss <br />Treatment of disturbed azea runoff will cause a decrease in peak flows in the Fish Creek and Foidel <br />Creek watersheds. However, any decrease due to retention in sedimentation ponds will be more than <br />offset by increased water downstream due to mine water discharge from the underground workings. <br />Increased levels of suspended solids will be minimized due to sedimentation ponds and NPDES <br />effluent limitations established for each point-source discharge from the mining operation. <br />Diversion of overland flow with ditches <br />Diversions will deprive small areas of water but will not significantly reduce flows downstream. <br />Induced rechazge or discharge by undergrround mine dewatering <br />Mine dewatering can cause changes in the natural process of stream discharge and rechazge. Mine <br />dewatering and gradient reversal may cause small decreases in Fish Creek and Foidel Creek stream <br />flows in and azound the mined area. Increased or modified rechazge is also possible due to subsidence. <br />Due to the small areal extent and the shale aquitards between the Wadge coal and the streams, <br />increased recharge would likely not be significant. <br />Subsidence impacts Middle, Foidel. Fish Creeks <br />Subsidence of portions of Middle, Foidel, and Fish Creeks will cause gradient changes in the streams. <br />These gradient changes will result in ponding and channel incision controlled by the streams' <br />relationships to orientation of the longwall panels and gateroads. Subsidence cracks in the neaz surface <br />also have the potential to disrupt the streamflow. Based on the presence of fine-grained alluvial <br />material, any disruption of stream flows would be temporary. Site-specific experience from Foidel <br />Creek resulted in a complete loss of streamflow for approximately 24 hours followed by a recovery <br />over the subsequent two months. <br />See Section B, part IIIB of this document for more information concerning the surface and ground <br />water monitoring plan. <br />The Division has evaluated each of these impacts and fmds that the operations proposed in the <br />application have been designed to prevent damage to the hydrologic balance outside the proposed <br />permit area (2.07.6(2)(c)). <br />13 <br />