2015-03-31_REPORT - C1992081 - Laserfiche WebLink

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The chronic selenium standard (4.6 ug /1) was exceeded once at upstream Site HGSD1; 5.6 ug /l in October. Downstream Site HGSD3 exceeded the chronic standard once; 7.0 ug /l in October. The acute standard (18.4 ug /1) was not exceeded at either site. Irrigation return water from the hay fields is in part the cause of the excursions at these sites. This entire area is composed of topsoils derived from the Lewis Shale, which has naturally elevated concentrations of selenium and dissolved solids. NPDES Sites did not flow this year, so they are not responsible for the stream selenium exceedances. HGT runs mercury tests with a Method Detection Limit (MDL) of 0.2 (or sometimes 0.4) ug /1. All test values this year were less than the MDL. 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. The sulfide values provided in Table 3 differ from the values reported in Appendix B. The sulfide data presented in Appendix B are the total of both the ionized (S ) and un- ionized (HS) 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. The results of those calculations are presented in Table 3 of this AHR. This year, no sulfide excursions occurred. Ground Water Ground water quality reports for this year are presented in Appendix B. Data provided includes a water quality report for this year, a water level report, sampling remarks and a listing of a regression plot of historic TDS data.