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0 Sulfide 1/1 <br />All iron excursions were the result of high suspended solids. None of <br />the iron excursions were at a NPDES site. One stream site, SSLG5, that <br />experienced am excursion is upstream of any mine discharges. <br />One stream sites, YSG5, exceeded the nitrite standard. This site is <br />downstream of the PSCM mining area; however, no NPDES sites experienced <br />an exceedance this year. Nitrites are unstable in aerated water and <br />will oxidize into nitrates (Hem, 1989). <br />Two samples from Site YSG5 (lower Grassy Creek) exceeded the chronic <br />selenium standard, 4.6 ug/l, with a values of 6.1 and 6.9 ug/1, but not <br />the acute standard, 18.4 ug/l. These high selenium values are coming <br />from Scotchman's Gulch, which is in contact with Lewis Shale soils. <br />Lewis Shale soils have contributed to the high selenium values observed <br />in many of the streams in this area. High selenium values are not <br />observed in any of the PSCM NPDES sites or spoil springs. <br />One sample from NPDES3 experienced exceedances of the sulfide standard <br />(0.002 mg/1 un-ionized), with a value of 0.0023 mg/l. The analytical <br />method detects both dissolved sulfides and acid-soluble metallic <br />sulfides present in suspended matter. It is suspected that a large <br />portion of the sulfides detected is of the latter type, which would bias <br />the un-ionized results high. Any dissolved sulfides present in surface <br />water should eventually oxidize to sulfates. <br />The sulfide values provided in Tables 13 and 15 differ from the values <br />reported in Appendix D. The sulfide data presented in Appendix D are the <br />total of both the ionized (S-) and un-ionized (H2S) forms of hydrogen <br />sulfide. The un-ionized form is the potentially toxic form, and is what <br />the CDPHE water quality standard is based upon. A procedure for <br />calculating the un-ionized form may be found on the website: <br />http•//www mullalyengineering.com.au/.images/product/file/Problem of Hydr <br />ogen Sulphide in Sewers.pdf page 5, Table 1. The results of those <br />calculations are presented in Tables 13 and 15 of this AHR. <br />19