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Seven samples exceeded the chronic selenium standard, 4.6 ug /l <br />(potentially dissolved). One of these samples also exceeded the acute <br />standard, 18.4 ug /l. Three of these excursions were at NPDESI2, with <br />values of 8.8, 7.9 and 8.9 ug /l. Two of these excursions were at <br />NPDESI3, with values of 14.2 and 25.5 ug /1. It is unknown as to why <br />these excursions occurred, although we suspect it may be due to the <br />record snowfall and rainfall, and near - record snowmelt runoff that <br />occurred in Routt County in winter and spring of 2011. Perhaps that <br />unusually high runoff somehow mobilized the selenium. See the following <br />NPDES Effluent section for a discussion of these excursions. <br />Two samples from Site YSG5 (lower Grassy Creek) exceeded the chronic <br />selenium standard, 4.6 ug /1, with values of 5.1 and 6.0 ug /l. The high <br />selenium values at Site YSG5 are in part coming from Scotchman's Gulch, <br />which is in contact with Lewis Shale soils. Lewis Shale soils have <br />contributed to the high selenium values observed in many of the streams <br />in this area. <br />Table 13 also shows selenium excursions in the dissolved and total <br />recoverable forms. SCC is performing these analyses voluntarily in order <br />to determine differences in the methods. They should not be considered <br />violations, as the required form for NPDES compliance is potentially <br />dissolved. <br />The sulfide data presented in Appendix D are the total of both the <br />ionized (S -) and un- ionized (H2S) 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.mullalyengineerLpg._com.au /images /product /file /Problem of Hydr <br />ogen Sulphide in Sewers.pdf page 5, Table 1. No excursions of the 0.002 <br />mg /l un- ionized sulfide standard occurred this year. <br />The aquatic life ammonia standard is dependent on pH and temperature. <br />The detection limit for ammonia is 0.05 mg /1. All values above detection <br />13 <br />