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Mercury <br /> The method detection limit for mercury (0.02 ug/L)used by SCC's lab is above the 0.01 ug/L <br /> aquatic life standard for mercury.None of the samples collected from YSSF3 or YSS2 during the <br /> last five years exceeded the labs method detection limit(Table 3 and Table 4). The CDPHE <br /> previously performed a reasonable potential analysis for Outfall 012 and 014 and determined that <br /> there was no reasonable potential for the discharges from these outfalls to exceed the mercury <br /> limit and the monitoring requirement was dropped from the permit. Total mercury is monitored <br /> quarterly(when discharge occurs) at Outfall 013. Between 2014 and 2018 none of the mercury <br /> samples collected from Outfall 013 (Range: 0.0017— 0.0036 µg/L; n=8)have exceeded the <br /> mercury standard (Table 17). <br /> Manganese <br /> The agricultural use dissolved manganese standard of 0.2 mg/L was exceeded twice at YSS2 <br /> (Table 8). The CWQCC Regulation 31 Manganese Agricultural Use Standard specifies that this <br /> standard is only applicable where irrigation water is applied to soils with pH lower than 6.0. In <br /> alkaline soils, as are found at Yoast Mine, a more appropriate standard would be 10 mg/L (EPA, <br /> 1976). Dissolved manganese at YSS2 ranged from 0.01 — 0.32 mg/L (mean: 0.09 mg/L) and is <br /> significantly lower than 10 mg/L.Neither of the samples exceeded the CHPHE Yampa Segment <br /> 13e acute or chronic manganese standards.No exceedances of the agricultural use or Segment <br /> 13e standards occurred at YSSF3. <br /> Selenium <br /> As noted in CWQCC Regulation 33, a temporary modification of the dissolved selenium chronic <br /> standard is in place for Yampa Segment 13e while additional information is collected to further <br /> evaluate the limited aquatic use and the extent of ambient sources of selenium within this <br /> segment. None of the samples collected from YSSF3 or YSS2 exceeded the Segment 13e acute <br /> selenium standard or the Regulation 31 agricultural use selenium standard. Although only the <br /> Segment 13e acute selenium standard and the Regulation 31 agricultural use water quality <br /> standards are compared to the water quality in Table 3 and 4, none of the samples collected at <br /> YSSF3 or YSS2 exhibited selenium concentrations above the Regulation 33 chronic selenium <br /> table value standard of 4.6 µg/L. <br /> SL-7 - 41 <br />