2013-02-21_REPORT - C2009087 - Laserfiche WebLink

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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. 2/3 Nitrite 1/1 Selenium 2/3 All iron excursions were the result of high suspended solids. None of the iron excursions were at a NPDES site. Site SSLG5 exceeded the nitrite standard (0.05 mg /1) with a value of 0.12 mg /1 in June. This site is upstream of mining. Nitrites are unstable in aerated water (Hem, 1989), and will oxidize to nitrates. The chronic selenium standard, 4.6 ug /l, was exceeded at two sites this year in the•Grassy Creek basin. Site SSLG5 (Little Grassy Creek upstream of mining) exceeded the standard once, with a value of 6.7 ug /1 in June. NPDES2 exceeded the standard two times, with values (in ug /l) of 5 (November) and 4.7 (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 (S1 and un- ionized (H forms of hydrogen sulfide. The un- ionized form is the potentially toxic form, and is what the CDPHE water quality standard is based upon. A procedure for calculating the un- ionized form may be found on the website: http: / /www.mullalyengineering.com.au /images /product /file /Problem of Hydr ogen Sulphide in Sewers.pdf page 5, Table 1. The results of those calculations are presented in Tables 13 and 15 of this ARR. The analytical method 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 type, which 18