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Tony Tennyson <br />Page 4 <br />November 12, 2020 <br />The Division did observe that concentrations of TDS in Good Spring Creek and Taylor Creek <br />continue to exceed the guideline of 1,500 mg/l. Also, concentration above this threshold were <br />reported for Jubb Creek and (to a lesser degree) for Collom Gulch. <br />The water quality standards in Table 2 were compared to the data within the 2018 and 2019 <br />AHRs for Colowyo. In this AHR review, metals that are reported as "total dissolved" are <br />compared to standards for dissolved metals. If Tri-State believes that this is inappropriate, <br />please inform the Division and also explain the rationale for reporting "total dissolved" <br />rather than "dissolved." <br />Good Spring Creek <br />The monitoring site below the Colowyo Mine on Good Spring Creek is LGSC. Based on a <br />comparison of LGSC data (in the 2018 and 2019 AHRs) and standards in Segment 3e, potential <br />issues were identified for iron and selenium. <br />One of the total dissolved iron concentration was 4.07 mg/l, significantly greater than 1.0 mg/l, <br />which is the total recoverable standard. However, a spatial analysis reveals that this is not <br />problematic. The upstream concentrations (monitoring location UWFGSC) are generally higher <br />than downstream (mine impacted) concentrations. As shown in the summary tables in the 2019 <br />AHR, the mean of the upstream iron concentrations is 1.43 mg/l, and the mean downstream is <br />0.65 mg/l. The maximum of the upstream iron concentrations is 9.86 mg/l, and the maximum <br />downstream is 8.84 mg/l. <br />The chronic standard for dissolved selenium is 4.6 µg/l, and all of the reported values in 2018 <br />and 2019 at LGSC exceed this value. However, as with iron, a spatial analysis reveals that this is <br />not problematic. The upstream selenium concentrations at UWFGSC are also higher than the <br />standard. <br />Taylor Creek <br />The sampling site below the Colowyo Mine on Taylor Creek is LTC. Based on a comparison of <br />LTC data and standards in Segment 3c., the only potential issue related to the CDPHE standards <br />is selenium. The chronic standard for dissolved selenium is 4.6 µg/l, and all of the reported <br />values in 2018 and 2019 at LTC exceed this value. However, a temporal analysis reveals that <br />this is not problematic, as many values recorded in the 1980s are also above this standard. <br />