2016-10-24_REPORT - C1994082 - Laserfiche WebLink

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day were all below 4.6 ug/1. However, the dissolved selenium value at Lower Scotchman Gulch Site G -SG -1A (part of a special selenium study) has been historically high. Scotchman Gulch flows over soils derived from the Lewis Shale, which are naturally high in selenium. This gulch joins Grassy Creek just upstream of Site YSGS. One NPDES site, NPDESI3, exceeded the potentially dissolved chronic standard, 4.6 ug/l, once this year. The potentially dissolved acute standard, 18.4 ug/l, was also exceeded once. However, this NPDES site has no selenium permit standard. The exceedances occurred on March 1011 and April 27th with values of 5.9 ug/l and 22.7 ug/l accordingly. The aquatic life ammonia standard is dependent on pH and temperature. The detection limit for ammonia is 0.05 mg/l. All values above detection limit are compared to table standards found on this website, page 87: https://nepis.epa.gov/Adobe/PDF/20003O3L.pdf No ammonia excursions occurred this year. The drinking water standard for mercury is 2 ug/l. The aquatic life standard for mercury is 0.01 ug/l, which is set to protect the average human consumer of fish. SCC runs two different mercury tests, a high level test with a MDL of 0.2 ug/l (for streams) and a low level test with a MDL of 0.0002 ug/l (for certain NPDES sites only). All high level test values this year were less than the detection limit, which is 0.2 ug/l. The sulfide data presented in Appendix D are the total of both the ionized (S-) and un -ionized (HzS) 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, page 5, Table 1: http://www.mullalyengineering.com.au/images/product/file/Problem of Hydr ogen Sulphide in Sewers.pdf No excursions of the 0.002 mg/l un -ionized sulfide standard occurred this year. 15