PERMFILE52147 - Laserfiche WebLink

Home Browse Search

• Rating Curves for non-USGS Stream Flow Stations. Flow measurements will be determined from stage readings recorded for a transect at each station and its corresponding rating curve. The rating curve for each station will be determined twice annually, once in the late spring or eazly summer, and once in the fall. If rating indicates the need for a new rating curve, then more frequent stream ratings will be performed. Mine Discharge Monitoring Mine water pumping sites. Underground mine water is pumped at two locations, Site 109 and Site 115. Site 109 is located near the main portals. Water pumped from 109 can either be discharged to Foidel Creek (via Pond D or F), or be used underground. Table A specifies sampling requirements for Site 109 discharges. Site 115 (FCB Treatment Facility) is located northwest of the main portals; it dewaters the majority of the mine. At 115, water collects in sump rooms and is then pumped up to the surface where it is passes through the water treatment facility. The discharge from 115 is then channeled to Fish Creek. IdPDES Permit CO-0042161 establishes the frequency of monitoring and the effluent limitations for 115. Flow meters monitor the quantity of mine dischazge at both pumping sites. Purpose of monitoring pumped water. An important objective of monitoring at Sites 109 and 115 is to ensure compliance with Trout Creek's 250 mg/1 instream sulfate standard. This standard applies year-round to Tmut Creek below Fish Creek, and applies June through February to the segment of Trout Creek between Middle and Fish Creeks. Site 115 monitoring has the additional objective of meeting the 1500 umhos/cm material damage standard for conductivity set by DMG on Fish Creek. As described below, mine pumping at Sites 109 and 115 is varied to prevent excessive chemical loading of Fish Creek and Trout Creek. Site 115's maximum pumping rate is determined by regulazly entering monitoring data into two series of stream loading calculations called the "Fish Creek Calculator" and the "Mine Discharge Calculator". Separate loading calculations are made for determining Site 109's maximum dischazge rate. • Conductivity as a sulfate indicator. Since it is difficult to accurately measure sulfate levels in the field, conductivity has been used as the indicator parameter for sulfate. In Exhibit 32, a[ the Station 69 node, [he dry season TDS and sulfate levels were modeled to be 412 and 174 mg/1 respectively. Using the conversion factor of 0.75, TDS is equivalent to a conductivity of 549 umhos/cm. The ratio of the sulfate to conductivity levels is estimated to be 0.32. The current stream standard of 250 mg/L is therefore equivalent to a conductivity of 780 umhos/cm. TCC selected 750 umhos/cm as a conservative standard to use in its calculator and this is considered a conservative estimate. Additional data may be used to correlate EC with sulfate and a new EC value could be used in the calculator . Monitoring and loading calculations for Trout Creek's 250 mgA instream sulfate standard. The "Contingent" monitoring in Table A includes monitoring aimed at preventing exceedances of Trout Creek's 250 mg/l sulfate standard. As described below, the monitoring varies depending on which underground pumping sites are discharging. Only Site 115 discharging - Weekly flow and EC data will be obtained from Sites 69, 115, and 1003, and EC from Site 1005, and then will be entered in the "Mine Dischazge Calculator' (see Table E49-26). The Mine Discharge Calculator determines Site 115's maximum discharge rate that will not cause an exceedance of Trout Creek's 250 mg/1 sulfate standard. For example, if the electrical conductivity at Sites ]003 and 1005 is • more than 750 umhos/cm, then TCC would not be able to discharge because the sulfate limit is already being exceeded (based on the 0.32 conductivity to sulfate relationship, described above). TCC will continue to review the EC/sulfate relationship and may • modify the EC value to reflect this review. In the event that the electrical conductivity is PR 04-06 Exhibit 14 - 3 5/03/04