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water during high flow (great dilution capacity) and lesser or no dischazge during periods of <br />low flow (minimal dilution capacity). <br />Lower Middle Creek -Impacts in this segment will be pronounced due to relatively small <br />instream flows. There is no sulfate or irrigation standazd over this reach. However, due to <br />standards on Trout Creek immediately below this segment, impacts will be minimized during <br />most times of the year. <br />Lower Fish Creek - The mine has the capacity to pump underground mine water into Fish <br />Creek at site 115. This pumping may significantly degrade water in Fish Creek and the water <br />in Trout Creek, downstream from Fish Creek. The degradation would be high concentrations <br />of dissolved solids, mainly sulfate. The Division applies a material damage standard to the <br />Fish Creek alluvial valley floor of 1500 umhos/cm. This standard is based on the salinity <br />level in imgation water that would cause a 3% drop in crop yield. Modeling indicates that <br />during low flow periods, the instream conductivity limit of 1500 umhos/cm could be <br />exceeded. Therefore, the applicant has committed to limiting mine water dischazge to a rate <br />that does not cause Fish Creek water to exceed 1500 umhos/cm. <br />Lower Trout Creek -The mine does not affect Trout Creek waters above the confluence with <br />Middle Creek, but the flow rate and quality of Trout Creek is affected by site 109 (Portal <br />area) dischazge into Foidel Creek. Foidel Creek flows into Middle Creek upstream of the <br />confluence of Middle Creek and Trout Creek. Modeling submitted during TR-32 review <br />indicates the potential for significant impact over the lower Trout Creek reach due to mine <br />water dischazges. Conductivity over this reach should not be a problem, as the highest <br />modeled value was 970 umhos/cm, which would not preclude irrigation usage. The sulfate <br />limit of 250 mg/I over the period of June to February could be exceeded. Therefore, the mine <br />will adjust discharge levels to prevent exceedance during this period in the same way <br />conductivity levels will be regulated on Lower Fish Creek. The mine demonstrated that <br />sulfate levels could be accurately determined by the existing relationship with conductivity <br />(sulfate/conductivity = 0.32). When conductivity at the upstream site (site 301) equals or <br />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 <br />mine water discharge from site 115 (Fish Creek borehole) and site 109 (portal discharge). <br />Modeling performed by the applicant in TR-32 indicates that during low flow, the sulfate <br />standard of 250 mg/1 could be exceeded due to mine water discharges. The applicant has <br />committed to conduct upstream and downstream water sampling to determine acceptable <br />discharge rates to maintain the sulfate levels below the 250 mg/1 in-stream standard. This <br />standard applies yeaz-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 would <br />not affect any current uses or exceed the in-stream standazds. <br />15 <br />