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lower Trout Creek from the confluence with Middle Creek to the confluence with Fish <br /> Creek due to mine water discharges. Conductivity over this reach should not be a <br /> problem, as the highest modeled value was 970 umhos/cm, which would not preclude <br /> irrigation usage. The sulfate limit of 250 mg/l over the period of June to February could <br /> be exceeded. Therefore, the mine will adjust discharge levels to prevent exceedance <br /> during this period in the same way conductivity levels will be regulated on Lower Fish <br /> Creek. The mine demonstrated that sulfate levels could be accurately determined by the <br /> existing relationship with conductivity (sulfate/conductivity=0.32). When conductivity at <br /> the upstream site on Trout Creek(site 301) equals or exceeds 740 umhos/cm, discharge <br /> from site 109 will cease entirely. <br /> Lower Trout Creek—Below Fish Creek—Flow rate and water quality will be affected by <br /> mine water discharge from site 115 and site 109 (Portal discharge). Modeling performed <br /> by the applicant(TR-32) indicates that during low flow, the sulfate standard of 250 mg/l <br /> could be exceeded due to mine water discharges. The applicant has committed to <br /> conduct upstream and downstream water sampling to determine acceptable discharge <br /> rates to maintain the sulfate levels below the 250 mg/l in-stream standard. This standard <br /> applies year round to this reach due to drinking water usage. Modeling indicates <br /> 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 <br /> Yampa River due to mine water discharges. The applicant predicts an increase in both <br /> dissolved solids and sulfate of approximately 9% over ambient levels. This increase <br /> would not affect any current uses or exceed the in-stream standards. <br /> Detention of surface water runoff in sedimentation ponds and related evaporation loss <br /> Treatment of disturbed area runoff will cause a decrease in peak flows in the Fish Creek and <br /> Foidel Creek watersheds. However, any decrease due to retention in sedimentation ponds <br /> will be more than offset by increased water downstream due to mine water discharge from <br /> the underground workings. Increased levels of suspended solids will be minimized due to <br /> sedimentation ponds and NPDES effluent limitations established for each point-source <br /> 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 <br /> downstream. <br /> Induced recharge or discharge by underground mine dewatering <br /> Mine dewatering can cause changes in the natural process of stream discharge and recharge. <br /> Mine dewatering and gradient reversal may cause small decreases in Fish Creek and Foidel <br /> Creek stream flows in and around the mined area. Increased or modified recharge is also <br /> possible due to subsidence. Due to the small areal extent and the shale aquitards between <br /> the Wadge coal and the streams, increased recharge would likely not be significant. <br /> Foidel Creek Mine 20 August 4,2023 <br />