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and May. This strict aquatic life standard was exceeded in. 38% of the <br />premining stream samples. <br />One sample from NPDES 012 exceeded the mercury standard, 0.01 ug/l, with <br />a value of 0.012 ug/l. High suspended solids in this sample (25 mg/1), <br />collected during snowpack runoff, may have interfered with this <br />analysis. <br />The same sample from NPDES 012 also exceeded the nitrite standard. <br />Nitrites are unstable in aerated water (Hem, 1989), and will oxidize to <br />nitrates. <br />Two samples from NPDES 012 exceeded the chronic selenium standard, 4.6 <br />ug/l. The acute standard, 18.4 ug/1, was not exceeded. <br />One sample from Site YSGF5 (Grassy Creek below Pond 011) experienced an <br />exceedance of the sulfide standard (0.002 mg/l un-ionized) this year. <br />This excursion occurred in September, when Pond 011 was not flowing. The <br />analytical method available to SCC detects both dissolved sulfides and <br />acid-soluble metallic sulfides present in suspended matter (102 mg/1 for <br />this sample). It is suspected that a large portion of the sulfides <br />detected is of the latter type, which would bias the un-ionized results <br />high. Any dissolved sulfides present in surface water should eventually <br />oxidize to sulfates. <br />NPDES Effluent Criteria (Permit No. CO-0000221). Three excursions of <br />NPDES effluent criteria occurred this year. These excursions occurred at <br />Pond 012 during high volume snowmelt runoff. Below is a summary of the <br />excursions. More details may be found in the July 24, 2008 cover letter <br />for the second quarter Discharge Monitoring Reports, of which the CDRMS <br />was copied. <br />1. A sample collected on April 22 (by Dan Mathews of the Colorado <br />Division of Mining, Reclamation and Safety) had a settleable solids <br />(STS) value of 0.9 ml/1. A STS sample collected by Seneca on April 23 <br />had a value of <0.4 ml/l. The effluent limit is 0.5 ml/l (daily max.) <br />13