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Lower Trout Creek - The mine does not affect Trout Creek waters above the confluence with Middle Creek, <br />but the flow rate and quality of Trout Creek is affected by site 109 (Portal area) discharge into Foidel Creek. <br />Foidel Creek flows into Middle Creek upstream of the confluence of Middle Creek and Trout Creek. <br />Modeling submitted during TR-32 review indicates the potential for significant impact over the lower Trout <br />Creek reach due to mine water discharges. Conductivity over this reach should not be a problem, as the <br />highest modeled value was 970 umhos/cm, which would not preclude irrigation usage. The sulfate limit of <br />250 mg/1 over the period of June to February could be exceeded. Therefore, the mine will adjust discharge <br />levels to prevent exceedance during this period in the same way conductivity levels will be regulated on <br />Lower Fish Creek. The mine demonstrated that sulfate levels could be accurately determined by the existing <br />relationship with conductivity (sulfate/conductivity--0.32). When conductivity at the upstream site (site 301) <br />equals or exceeds 740 umhos/cm, discharge from site 109 will cease entirely. <br />Lower Trout Creek - Below Fish Creek - Flow rate and water quality will be affected by mine water <br />discharge from site 115 and site 109 (Portal discharge). Modeling performed by the applicant (TR-32) <br />indicates that during low flow, the sulfate standard of 250 mg/1 could be exceeded due to mine water <br />discharges. The applicant has committed to conduct upstream and downstream water sampling to determine <br />acceptable discharge rates to maintain the sulfate levels below the 250 mg/l in-stream standard. This <br />standard applies year round to this reach due to drinking water useage. Modeling indicates conductivity (964 <br />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 due to <br />mine water discharges. The applicant predicts an increase in both dissolved solids and sulfate of <br />approximately 9% over ambient levels. This increase would not affect any current uses or exceed the in- <br />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 Foidel Creek <br />watersheds. However, any decrease due to retention in sedimentation ponds will be more than offset by <br />increased water downstream due to mine water discharge from the underground workings. Increased levels <br />of suspended solids will be minimized due to sedimentation ponds and NPDES effluent limitations <br />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 recharge. Mine <br />dewatering and gradient reversal may cause small decreases in Fish Creek and Foidel Creek stream flows in <br />and around the mined area. Increased or modified recharge is also possible due to subsidence. Due to the <br />small areal extent and the shale aquitards between the Wadge coal and the streams, increased recharge would <br />likely not be significant. <br />14