2011-02-25_REPORT - C1994082 - Laserfiche WebLink

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One sample from Site YSG5 exceeded the nitrite standard. Nitrites are unstable in aerated water (Hem, 1989), and will oxidize to nitrates. No excursions occurred at NPDES outfalls. Three samples exceeded the chronic selenium standard, 4.6 ug/l. No samples also exceeded the acute standard, 18.4 ug/1. The one excursion at a NPDES outfall was at Pond 012, with a value of 5.0 ug/1, only 0.4 ug/1 above the chronic standard. Two samples from Site YSG5 (lower Grassy Creek) exceeded the chronic selenium standard, 4.6 ug/1, with values of 6.1 and 6.9 ug/1. The high selenium values at Site YSG5 are coming from Scotchman's Gulch, which is in contact with Lewis Shale soils. Lewis Shale soils have contributed to the high selenium values observed in many of the streams in this area. The sulfide data presented in Appendix D are the total of both the ionized (S-) and un-ionized (H2S) 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. No excursions of the 0.002 mg/l un-ionized sulfide standard occurred this year. The aquatic life ammonia standard is dependent on pH and temperature. The detection limit for ammonia is 0.05 mg/1. All values above detection limit are compared to table standards found on this website, page 87: http://www.epa.gov/waterscience/criteria/ammonia/99update.pdf No ammonia excursions occurred this year. SCC runs two different mercury tests, a high level test with a MDL of 0.2 ug/l (for streams and NPDES sites) and a low level test with a MDL of 0.0002 ug/l (for NPDES sites only). All high level test values this year were less than 0.2 ug/1. All low level tests were below the 0.01 ug/l stream standards. • 13