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Creek. The NPDES Permit CO-0042161 establishes the frequency of monitoring and the effluent limitations for Site l I5. At both sites, flow meters have been installed to monitor the quantity of mine discharge. (,:,~, Since it is difficult to accurately measure sulfate levels in the field, conductivity has been used as the indictor parameter for sulfate. In Exhibit 32, at the Station 69 node, the dry season TDS and sulfate levels were modeled [o be 412 and 174 mg/L 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. When either Site 115 or Site 109 is discharging, additional monitoring of surface water sites will be performed to prevent exceedances of the in-stream sulfate limit (presently 250 mg/L) on Trout Creek below Fish Creek and on Trout Creek between Middle and Fish Creek from June through February. Also, when Site 115 is discharging additional surface water monitoring will be performed to prevent exceeding the material damage level for conductivity set for Fish Creek of 1500 umhos/cm. The EC and sulfate data will be forwarded to the Division on a quarterly basis for the period of l" quarter, 2000 through 1" quarter 2001. The data will be submitted within 45 days of the end of the respective quarter. The additional monitoring for Site l l5 will include flow and electrical conductivity measurements at Site 16, Site 115, and electrical conductivity at a site immediately downstream of Site 115. This monitoring will be wnducted on a weekly schedule. The data obtained from Site 16 and the electrical conductivity from Site 115 will be input into the "Fish Creek Calculator" (see Table E49-25) to determine rate of discharge allowed from Site I15 to prevent material damage to the downstream Fish Creek AVF. During the winter months, when Site 16 is iced over, flow data from USGS station 09239500 will be used to estimate the flow at Site 16, and this value will be used in the "Fish Creek Calculator". The discussion concerning winter measurement relationships for Site l6 is presented below. (' '_, The other aspect of monitoring discharge from Site 115 addresses compliance with the sulfate standard on Trout Creek below Fish Creek. The present standard is 250 mg/L. For this aspect of the plan, additional monitoring will be conducted at Sites 69, 115, 1003 and 1005. At Sites 69, 115 and 1003 both flow and electrical conductivity will be monitored, while at Site 1005 electrical conductivity will be monitored. This additional monitoring will be conducted on a weekly schedule. The data obtained from Sites 69, 115, 1003 and 1005 will be used in the "Mine Discharge Calculator" (see Table E49-26) to determine rate of discharge from Site 115. For example, if the electrical conductivity at Sites 1003 and 1005 is over 750 umhos/cm then TCC would not be able to discharge because the sulfate limit is already being exceeded. In the event that the electrical conductivity is below 750 umhos/cm then the evaluation would be made as to the rate at which effluent can be discharged into Fish Creek and maintain compliance with the sulfate standard on Trout Creek. The winter flow estimates will be as described below for Sites 69 and 1003. Between June and February, when Site 109 is discharging and the discharge is entering Foidel Creek, Site 69 will be monitored for flow rate and conductivity weekly and Site 301 will be monitored for conductivity weekly. This data will be used to determine the rate of discharge from Site 109. When both Sites 109 and l l5 are discharging the additional monitoring work will involve obtaining flow and electrical conductivity measurements from Sites 69, 1005, 109 and 115. The data will be entered into the Mince Discharge Calculator to determine the discharge rate from both Sites 109 and 115. The results may be that TCC can only discharge from one, both or neither of the sites. The calculator will determine those rates and the above described monitoring will verify the accuracy of the calculator. During the winter, when ice conditions prevent accurate measurement of surface water Flow rate, they will be estimated using a relationship with the USGS station on the Yampa River below Steamboat Springs (09239500). ~ Phis data is available on an instantaneous basis year-round on the Internet (http//nwis-colo.cr.usgs.gov/rt- cgi/gen_st~rg?station=09239500). Since there is insufficient data from Site 1005 to develop a relationship, a TR99-32 E.stt 14.4 APPROy~~ ~=B r. g 2000 1/28/00