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Seneca 11 Mine <br />SL -6 Phase III Bond Release Request <br />June 2014 <br />this standard occurred at SSC10, SSB12, NPDES4 or NPDES8 discharges. Therefore, this <br />excursion on Fish Creek was not caused by either mining operation. Nitrites are unstable in <br />aerated water (Hem, 1989), and will oxidize to nitrates. <br />Five out of thirty six samples from NPDES8 exceeded the chronic selenium standard of 4.6 ug /1, <br />with values between 5.9 and 17 ug /1. The potentially dissolved (PD) method is the method that is <br />required for NPDES compliance. The dissolved (D) selenium method is used for assessing <br />stream compliance, and was also sometimes run as a quality control check. The total recoverable <br />(TR) selenium method was run as a quality control check. The acute standard, 18.4 ug /1, was not <br />exceeded in the PD form. No selenium exceedances occurred at any surface water sites <br />downstream of NPDES8. <br />No excursions of NPDES effluent criteria occurred in the past three years. For NPDES8, the <br />five excursions of the selenium stream standard noted above were not NPDES permit limit <br />excursions. The permit limit for this outfall for selenium is to "Report" only. This outfall has a <br />NPDES Compliance Schedule in the Seneca II Mine CDPS Permit (No. CO- 0000223) to meet <br />the selenium limit by December 31, 2015. Seneca is currently investigating means of selenium <br />control for discharges from NPDES8. SCC conducted aquatic life surveys in this drainage during <br />2012 and 2013, and found limited and only seasonal occurrence of fish in the lower reach of <br />Bond Creek. Accordingly, SCC is developing a proposed revision to the stream classifications <br />and water quality standards under the Colorado Department of Public Health Regulation 33 for <br />the upcoming June 9, 2014 Upper Colorado River Basin Hearing with the Colorado Water <br />Quality Control Commission. <br />The sulfide values provided in Table 5 differ from the values reported in Table 4. The sulfide <br />data presented on Table 4 are the total of both the ionized (S) and un- ionized (HS) forms of <br />hydrogen sulfide. The un- ionized form is the potentially toxic form, and is what the CDPHE <br />water quality standard is based upon. A procedure for calculating the un- ionized form may be <br />found on the website: <br />http : / /www.mullalyengineering.com.au /images /product /file /Problem of Hydrogen Sulphide <br />in Sewers.pdf at page 5, Table 1of that document. The results of those calculations are presented <br />28 <br />