2012-04-27_REPORT - C2009087 (2)

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Two samples from NPDES4 exceeded the chronic selenium standard, 4.6 ug /l, in May and June, with values of 14 and 8 ug /l, respectively. The acute standard, 18.4 ug /1, was not exceeded. See the following NPDES effluent section for more details. 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 14 shows the new CDPHE receiving stream standards for Grassy Creek. Table 15 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. 5/8 Selenium 4/10 All iron excursions were the result of high suspended solids. None of the iron excursions were at a NPDES site. One stream site, SSLG5, that experienced am excursion is upstream of any mine discharges. The chronic selenium standard, 4.6 ug /1, was exceeded at four sites this year in the Grassy Creek basin. Site SSLG5 (Little Grassy Creek upstream of mining) exceeded the standard twice with values of 16.7 and 11.0 ug /l in June and September, respectively. NPDES2 exceeded the standard five times, with values (in ug /1) of 5 (April), 11 (May), 7 (June), 6 (July) and 5 (August). Site SSG2 (lower Grassy Creek) exceeded the standard once in May with a value of 7.4 ug /l. Site YSG5 (furthest downstream site on Grassy Creek) exceeded the standard twice with values of 6 ug /l in May and 5.1 ug /1 in June. The acute standard, 18.4 ug /1, was not exceeded at any site. Selenium excursions will be discussed below in the NPDES effluent section. No sites exceeded the sulfide standard this year. The sulfide values provided in Tables 13 and 15 differ from the values reported in Appendix D. The sulfide data presented in Appendix D are the total of both the ionized (S - ) and un- ionized (H forms of hydrogen sulfide. The un-- 18