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4.2 SAGE CREEK <br /> Analytical results for the 2020 surface water monitoring conducted at Sage Creek <br /> stream point WSSF3 is provided in Table D.7 of Appendix D and the analytical results <br /> for the two outfalls that report to Sage Creek outfalls are included in Table D.B. <br /> There were no exceedances of any NPDES permit limits or Yampa Segment 13e water <br /> quality standards at the two Sage Creek NPDES Outfalls in 2020. Total recoverable <br /> iron exceeded the Yampa Segment 13e surface water quality standard twice at WSSF3 <br /> in 2020. The iron in these samples (1.04 - 1.47 mg/L) was just above the water quality <br /> standard. The pH in both samples was alkaline but the total suspended solids (range: <br /> 31 - 44 mg/L; mean: 37.5 mg/L) was elevated relative to historic levels (range: 2010- <br /> 2019: <5 - 21 mg/L; mean: 9.5 mg/L). The SIIW drainage area that reports to Sage <br /> Creek has been vegetated and stable for over a decade and the slightly elevated iron <br /> may be the result of natural erosion in the unaffected portions of the watershed or <br /> the sampler could have accidentally disturbed the base of the stream channel while <br /> collecting the sample. As discussed in Section 4.1, the lab used by SCC has a method <br /> detection limit for mercury and sulfide that are above the Segment 13e water quality <br /> standard. None of the samples collected from WSSF3 in 2020 exceed the labs mercury <br /> or sulfide method detection limit. <br /> In the Probable Hydrological Consequences (PHC, Tab 17) section of the SIIW PAP, <br /> predictions were made for the expected TDS increases to be observed at several <br /> stream points. The following table outlines these predictions along with this year's <br /> average concentration. <br /> Stream Point Predicted TDS (mg/L) Mean TDS (mg/L)* <br /> WSHF1 2527 2340 <br /> WSD5 2451 1820 <br /> WSSF3 1 626** 1 945 <br /> * Duplicates removed from average calculation <br /> ** Predicted TDS value does not account for later contributions from Yoast Mine (C-1994-082). <br /> Predicted TDS concentration at WSSF3 in Yoast Mine PHC is 2118 mg/L. <br /> The annual average TDS measured at Dry Creek monitoring points WSHF1 and WSD5 <br /> were below the concentrations predicted in the SIIW PHC. Although the TDS at Sage <br /> Page 13 of 17 <br />