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ug /l in April. NPDES4 exceeded the standard twice in April and May, with <br />values of 8.8 ug /l and 9.7 ug/l respectively. The acute standard, 18.4 <br />ug /1, was not exceeded at any site. Selenium excursions will be <br />discussed below in the NPDES effluent section. <br />No sites exceeded the sulfide standard this year. The sulfide values <br />provided in Tables 13 and 15 differ from the values reported in Appendix <br />D. The sulfide data presented in Appendix D are the total of both the <br />ionized (S ) and un- ionized H-.S) forms of hydrogen sulfide. The un- <br />ionized form is the potentially toxic form, and is what the CDPHE water <br />quality standard is based upon. A procedure for calculating the un- <br />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. The <br />analytical method detects both dissolved sulfides and acid - soluble <br />metallic sulfides present in suspended matter. It is suspected that a <br />large portion of the sulfides detected is of the latter type, which <br />would bias the un- ionized results high. Any dissolved sulfides present <br />in surface water should eventually oxidize to sulfates. <br />No sites exceeded the ammonia standard this year. The aquatic life <br />ammonia standard is dependent on pH and temperature. The detection limit <br />for ammonia is 0.05 mg /1. All values above detection limit are compared <br />to table standards, page 87, found on this website: <br />htl;p / /www.epa.gov /waterscience /criteria /ammonia /99update.pdf <br />The drinking water standard for mercury is 2 ug"l. The aquatic life <br />standard for mercury is 0.01 ug /1, which is set to protect the average <br />human consumer of fish. PSCM's lab uses a method with a detection limit <br />of 0.2 ug /1. None of the samples collected this year were above the <br />detection limit. During the last NPDES permit renewal, the CDPHE <br />performed a reasonable potential analysis on PSCM's outfalls. It <br />determined that there was no reasonable potential for PSCM's outfalls to <br />exceed the mercury limit; therefore, mercury monitoring is no longer <br />required for PSCM's outfalls. <br />19 <br />