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Discharge of mine inflow water to surface water drainages <br />Mine water discharged to [he surface water system will increase the conductivity, total dissolved solids <br />(TDS), sulfate, and iron concentrations in the streams receiving the discharge. Total suspended solids, <br />SAR, and pH could also increase due to these discharges. SAR may reach up to 6.2 in Fish Creek and 3.0 <br />in Trout Creek. Sulfate and conductivity impacts are predicted for various segments of the stream system <br />to be affected. TR-32 approved a plan which will allow the mine to discharge considerable volumes of <br />degraded water during high flow (great dilution capacity) and lesser or no discharge during periods of fow <br />Flow (minimal dilution capacity). <br />Lower Middle Creek -Impacts in this segment will be pronounced due to relatively small instream Flows. <br />There is no sulfate or irrigation standard over this reach. However, due to standards on Trout Creek <br />immediately below this segment, impacts will be minimized during most times of the year. <br />Lower Fish Creek-The potential for significant impacts to lower Fish Creek, from mine water discharge <br />site ! l5 (Fish Creek dewatering facility) downstream to the confluence with Trout Creek, exists. <br />Although no sulfate standard applies over this reach, Fish Creek and adjacent alluvial valley floor areas aze <br />held to a 1500 umhos/cm material damage standard for irrigation waters. Modeling indicates that during <br />low flow periods, the instream conductivity limit of 1500 umhos/cm could be exceeded. Therefore, the <br />applicant has committed to maintain its mine water discharge rate from site 1 l5 at a level which would <br />prevent material damage (<1500 umhos/cm) by measuring upstream flow and quality and computing a <br />discharge rate which would prevent downstream exceedance of the conductivity limit for irrigation waters. <br />The sulfate standard for drinking water of 250 mg/1 does not apply over this reach. <br />Lower Trout Creek -The mine does not affect Trout Creek waters above the confluence with Middle <br />Creek, but the Flow rate and quality of'frout Creek is affected by site 109 (Portal area) discharge into <br />Foidel Creek. Foidel Creek flows into Middle Creek upstream of the confluence of Middle Creek and <br />Trout Creek. Modeling submitted during TR-32 review indicates the potential for significant impact over <br />the lower Trout Creek reach 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 irtigation usage. <br />The sulfate 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 conductivity levels <br />will be regulated on Lower Fish Creek. The mine demonstrated that sulfate levels could be accurately <br />determined by the existing relationship with conductivity (sulfate/conductivity=.32). When conductivity <br />at the upstream site (site 301) equals or exceeds 740 umhos/cm, discharge from site 109 will cease <br />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/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 dischazge rates to maintain the sulfate levels below the 250 mg/l in-stream standard. <br />This standard applies year round to this reach due to drinking water useage. 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 Yampa River due <br />to 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 />C:U H B\C82056\RN03\RN03FI ND.doc <br />15 <br />