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selenium (dissolved, total recoverable and potentially dissolved) from 2011 through 2015 were <br />higher than the standard. One sample at YSG5 exceeded the dissolved chronic selenium <br />standard of 4.6 ug/1, with a value of 4.9 ug/l on 4/29/2013. A sample collected the same day <br />upstream at steam Site G -SG -1A, a temporary surface water monitoring site established on lower <br />Scotchman's Gulch during 2013 as part of a special selenium study, displayed a PD selenium <br />value of 15.6 ug/l. The Scotchmans Gulch confluence with Grassy Creek approximately one- <br />quarter mile upstream of Site YSG5, and runoff from Scotchman's Gulch and its associated <br />tributaries flow over soils derived from the Lewis Shale, which is naturally high in selenium. Site <br />YSG5 is out of compliance using the CDPHE 303d listing criteria (85`'' percentile) of PD <br />selenium values over the past five years (2010-2014) with a PD value of 6.14 ug/1(dissolved <br />values were only recently being collected at this site). The high selenium concentrations measured <br />at temporary surface water monitoring sites established on Scotchman's Gulch and tributaries <br />during 2013 indicate these drainagesare causing the high selenium concentrations measured at <br />Site YSG5. <br />The sulfide values provided in Tables 7 and 10 differ from the values reported in Tables 6 and 9. <br />The sulfide data presented on Tables 6 and 9 are the total of both the ionized (S) and un -ionized <br />(HZS) forms of hydrogen 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 calculating the un -ionized <br />form may be found on the website: <br />http://muUal, eenn&eering.com.au/images/product/file/45/Problem of Hydrogen Su <br />hide in Sewers.pdf (Refer to page 5, Table 1 on the website document). <br />The results of those calculations are presented in Tables 7 and 10. No sites exceeded the sulfide <br />standard (0.002 mg/1) in the past five years. The analytical method detects both dissolved sulfides <br />and acid -soluble metallic sulfides present in suspended matter. It is suspected that a large portion <br />of any sulfides detected is of the latter type, which would bias towards higher un -ionized results. <br />Any dissolved sulfides present in surface water should eventually oxidize to sulfates. <br />The aquatic life ammonia standard is dependent on pH and temperature. The detection limit for <br />ammonia is 0.05 mg/1. All values above the detection limit are compared to table standards, page <br />30 <br />