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HGSD1 is most likely the cause of the excursion at that site. This <br />entire area is composed of topsoils derived from the Lewis Shale, which <br />has naturally elevated concentrations of selenium and dissolved solids, <br />which explains the increase in selenium noted at downstream Site HGSD3. <br />HGT runs mercury tests with a Method Detection Limit (MDL) of 0.2 (or <br />sometimes 0.4) ug /l. All test values this year were less than the MDL. <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 />limit are compared to table standards found on this website, page 87: <br />http:/ /www.epa.gov /waterscience /criteria /ammonia /99update.pdf <br />No ammonia excursions occurred this year. <br />The sulfide values provided in Table 3 differ from the values reported <br />in Appendix B. The sulfide data presented in Appendix B are the total of <br />both the ionized (S -) and un- ionized (HZS) forms of hydrogen sulfide. <br />The un- ionized form is the potentially toxic form, and is what the CDPHE <br />water quality standard is based upon. A procedure for calculating the <br />un- ionized form may be found on the website: <br />http: / /www.mullalyengineerinq.com.au /images /product /file /Problem of Hydr <br />ogen Sulphide in Sewers.pdf page 5, Table 1. The results of those <br />calculations are presented in Table 3 of this AHR. This year, no sulfide <br />excursions occurred. <br />Ground Water <br />Ground water quality reports for this year are presented in Appendix B. <br />Data provided includes a water quality report for this year, a water <br />level report, sampling remarks and a listing of a regression plot of <br />historic TDS data. <br />Well HGDAL3 is downgradient of the Loadout. It was drilled in 1993. It <br />displays an increasing TDS trend; however, the peak TDS value occurred <br />in June 1997. <br />4 <br />