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indicates that during low flow, the sulfate standard of 250 mg/I could be exceeded due to mine water <br />discharges. The applicant has committed to conduct upstream and downstream water sampling to <br />determine acceptable discharge rates to maintain the sulfate levels below the 250 mg/I in-stream <br />standard. This standard applies year-round to this reach due to drinking water usage. Modeling <br />indicates conductivity (964 umhos/cm and SAR 2.4 highest modeled) should 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 Hoods and related evaporation loss <br />Treatment of disturbed area 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 recharge or discharge by underground 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 around the mined area. Increased or modified recharge is also possible due to subsidence. <br />Due to the small areal extent and the shale aquitazds between the Wadge coal and the streams, <br />increased recharge would likely not be significant. <br />Subsidence imnacts on Foidel and Middle Creeks <br />Subsidence of portions of Foidel Creek and Middle Creek will cause gradient changes in the streams. <br />These gradient changes will result in ponding and channel incision controlled by the streams <br />relationship to orientation of the longwall panels and gateroads. Subsidence cracks in the near surface <br />also have the potential to disrupt the streamflow. Based on the presence offine-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 finds that the operations proposed under 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 />4. The Division finds that the affected area is, subject to valid rights existing as of August 3, 1977, not <br />within: <br />13 <br />