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Mine Discharge Monitoring <br />Mine Water Pumping Sites Underground mine water is pumped at two locations, Site 109 and Site 115. Site 109 <br />is located near the main portals. Water pumped from 109 can either be dischazged to Foidel Creek (via Pond D or <br />F), or be used underground. Table A specifies sampling requirements for Site 109 discharges. Site 115 (FCB <br />Treatment Facility), which dewaters the majority of the mine, is located northwest of the main portals. At Site 115, <br />water that collects in the downgradient sealed mine workings is pumped to the surface, where it is passes through <br />the water treatment facility. The treated discharge from Site 115 is then channeled to Fish Creek. NPDES Permit <br />CO-0042161 establishes the frequency of monitoring and effluent limitations for Site 115. Flow meters monitor the <br />quantity of mine discharge at both pumping sites. <br />Purpose of Monitoring Pumped Water An important objective of monitoring at Sites 109 and 115 is to assure <br />compliance with Trout Creek's 250 mg/1 in-stream sulfate standard. This standard applies year-round to Trout <br />Creek below Fish Creek, and applies June through February to the segment of Trout Creek between Middle and <br />Fish Creeks. Site 115 monitoring has the additional objective of meeting the 1,500 umhos/cm material damage <br />standard for conductivity set by DMG on Fish Creek. As described below, mine pumping at Sites 109 and 115 is <br />varied to prevent excessive chemical loading of Fish Creek and Trout Creek. Maximum discharge rates for Site <br />] 15 is determined by regularly entering monitoring data into two series of stream-loading calculations called the <br />"Fish Creek Calculator" and the "Mine Discharge Calculator". Sepazate loading calculations are made to determine <br />the maximum dischazge rate for Site 109. <br />Conductivity as a Sulfate Indicator Since it is difficult to accurately measure sulfate levels in the field, <br />conductivity has been used as the indicator parameter for sulfate. In Exhibit 32, at the Station 69 node, the dry <br />season TDS and sulfate levels were modeled to be 412 and 174 mg/1 respectively. Using the conversion factor of <br />0.75, TDS is equivalent to a conductivity of 549 µrnhos/cm. The ratio of the sulfate to conductivity levels is <br />estimated to be 0.32. The current stream standard of 250 mg/L is therefore equivalent to a conductivity of 780 <br />µmhos/cm. TCC selected 750 µmhos/cm to use in its calculator as a conservative standard. Additional data may <br />be used to correlate EC with sulfate in the future, in which case, a new EC value could be developed for use in the <br />. calculator. <br />Monitoring and Loadi~tg Calculations for the 250 mgR Trout Creek In-Stream Sulfate Standard The <br />"Contingent" monitoring in Table A includes monitoring aimed at preventing exceedances of the 250 mg/1 sulfate <br />standard for Trout Creek. As described below, the monitoring varies depending on which underground pumping <br />sites aze dischazging. <br />Only Site 115 discharging -Weekly flow and EC data will be obtained from Sites 69, 115, <br />and 1003, and EC from Site 1005, and then will be entered in the "Mine Dischazge <br />Calculator" (see Table E49-26). The Mine Discharge Calculator is used to detemune the <br />maximum dischazge rate for Site 115 that will not cause an exceedance of the 250 mg/1 <br />sulfate standard for Trout Creek. For example, if the electrical conductivity at Sites 1003 <br />and 1005 is more than 750 µmhos/cm, TCC would not be able to dischazge because the <br />sulfate limit is already being exceeded (based on the 0.32 conductivity to sulfate <br />relationship, described above). TCC will continue to review the EC/sulfate relationship <br />and may modify the EC value to reflect this review. In the event that the electrical <br />conductivity is below 750 µmhos/cm, then the evaluation would be made as to the rate at <br />which effluent can be discharged to Fish Creek and maintain compliance with the sulfate <br />standard on Trout Creek. The winter flow estimates will be as described below for Sites 69 <br />and 1003. <br />Only Site 109 discharging -Between June and February, when only Site 109 is <br />discharging and the discharge is entering Foidel Creek, weekly monitoring will be <br />• performed at Site 69 for flow rate and conductivity, and at Site 301 for conductivity. This <br />data will be used for calculating the maximum rate of discharge from Site 109. <br />MRO6-208 Exhibit 14 - 3 07/26/06 <br />