2010-03-22_REPORT - C1980005 (2)

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Selenium 1/1 9 All iron excursions were the result of high suspended solids. None of the iron excursions were at a NPDES site. One sample from NPDES8 exceeded the chronic selenium standard, 4.6 ug/1, with a value of 7.1 ug/l, but not the acute standard, 18.4 ug/1. In September 2003, the CDPHE resegmented Grassy Creek from Yampa Segment 12 to Segment 13e. Regulation 33 was further revised in December 2005 and August 2008. Table 15 shows the new CDPHE receiving stream standards for Grassy Creek. Table 16 provides a comparison of those standards to water quality data collected this year from NPDES and stream sites in the Grassy Creek basin. Standards that were exceeded are: Parameter # of Sites / # of Excursions Iron, Total Rec. 3/4 Nitrite 1/1 Selenium 1/1 Sulfide 2/4 All iron excursions were the result of high suspended solids. None of the iron excursions were at a NPDES site. The two stream sites that experienced excursions are upstream of Seneca's discharges. One stream site, SSLG5, exceeded the nitrite standard. This site is upstream of the Seneca II mining area. Nitrites are unstable in aerated water and will oxidize into nitrates (Hem, 1989). This same site exceeded the chronic selenium standard. Three samples from NPDES3 experienced exceedances of the sulfide standard (0.002 mg/l un-ionized), as well as one sample from Site SSG2. i The analytical method available to SCC detects both dissolved sulfides and acid-soluble metallic sulfides present in suspended matter. It is suspected that a large portion of the sulfides detected is of the latter i20