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Hubberson Gulch stream points. Although the total recoverable chronic water quality standard was <br /> exceeded frequently at WSH7 and W SHF 1, the iron in the samples collected during the last five years did <br /> not exceed the pre-mine concentrations measured at W SHF 1 and only exceeded the pre-mine <br /> concentrations measured at WSH7 once. <br /> Total recoverable iron was monitored at Outfalls 016 and 017 during 10 of the 15 WSH7 (SW-S2W-SG7) <br /> monitoring events (Table 18). This included nine of the 13 events that total recoverable iron exceeded the <br /> water quality standard at WSH7 (SW-S2W-SG7). During all nine of those events the total recoverable <br /> iron measured at Outfalls 016 and 017 met the Yampa Segment 13d surface water quality standard and <br /> was an order of magnitude less than the concentration measured downstream at WSH7 (SW-S2W-SG7). <br /> Similarly, total recoverable iron was measured at Outfall 006 during eleven of the 22 WSHF1 <br /> (SW-S2W-FG1) monitoring events (Table 19). During six of these events the total recoverable iron <br /> exceeded the water quality standard at WSHF1(SW-S2W-FG1). Total recoverable iron at Outfall 006 <br /> ranged from<0.1 —0.16 mg/L during the eleven events,never exceeding the Yampa Segment 13d surface <br /> water quality standard. This indicates that the elevated iron at WSH7 (SW-S2W-SG7) and WSHF1 <br /> (SW-S2W-FG1)is unrelated to runoff from the mine <br /> Total recoverable iron is strongly correlated with suspended solids at stream points WSH7 (r2: 0.92) and <br /> WSHF1 (r2: 0.97) (Figure 2). As described in the Phase II Suspended Solids Evaluation, TSS in the <br /> effluent of the NPDES outfalls is typically one to two orders of magnitude less than the concentrations <br /> observed at the stream points. Furthermore, the post mine effluent TSS concentrations do not exceed the <br /> stream points pre-mine concentrations. This indicates that the iron observed at WSH7 and WSHF1 is <br /> unrelated to runoff from the reclaimed mine and is more likely the result of natural erosion that is <br /> occurring from the unaffected portion of the watershed. <br /> Ammonia, Nitrogen <br /> The CDPHE Yampa Segment 13d ammonia, nitrogen water quality standard of 0.05 mg/L, which is the <br /> laboratories detection limit, was exceeded once at WSD5 (SW-S2W-SG5). The aquatic life ammonia <br /> standard, as established by USEPA, is dependent on both the pH and temperature of the surface water <br /> body. The sample was compared to the temperature and pH dependent values of the chronic criterion <br /> found in Table 6 of USEPA's 2013 Aquatic Life Ambient Water Quality Criteria for Ammonia — <br /> Freshwater (USEPA 2013). The measured value of 0.13 mg/L did not exceed the 1.25 mg/L chronic <br /> aquatic life criteria for surface waters with pH of 8.2 standard units and temperature of 7.6 degrees <br /> Celsius. <br /> Sulfide <br /> The method detection limit for the sulfide analysis (MDL: 0.02 mg/L) conducted by SCC's lab exceeds <br /> the CDPHE Yampa Segment 13d water quality standard for un-ionized sulfide (0.002 mg/L). This <br /> analytical method detects both dissolved sulfides and acid-soluble metallic sulfides that are present in <br /> suspended matter and provides a single cumulative concentration that includes both the ionized (HS-) and <br /> un-ionized forms of hydrogen sulfide(H2S). The un-ionized hydrogen sulfide is the potentially toxic form <br /> which CDPHE based the water quality standard on. The distribution of sulfide between the un-ionized <br /> hydrogen sulfide and ionized form is dependent on the temperature and pH. At low pH most of the total <br /> 17 <br />