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Tony Tennyson <br />Page 5 <br />November 12, 2020 <br />Jubb Creek <br />The sampling site below the Colowyo Mine on Jubb Creek is CJC. Based on a comparison of <br />CJC data and standards in Segment 3g., the only potential issue related to the CDPHE standards <br />is iron. The standard for total recoverable iron is 1.0 mg/1, and reported dissolved iron values in <br />2018 and 2019 at CJC exceed this value (including 2.61 mg/l in November of 2018 and 8.93 <br />mg/l in 2019). A spatial analysis reveals that the values at WFJC, adjacent to the mine on Jubb <br />Creek, are below this standard, and a temporal analysis reveals that most of the iron <br />concentrations at CJC prior to 2018 were below the standard. Please address this potential <br />issue with iron in Jubb Creek. The Division recognizes that only a limited amount of <br />disturbance related to the Colowyo Mine impacts this creek at CJC. <br />Collom Gulch <br />The sampling site below the Colowyo Mine on Collom Gulch is LCG. Based on a comparison <br />of LCG data and standards in Segment 3g., there are no apparent issues with water quality within <br />this receiving water. <br />REVIEW OF GROUNDWATER QUALITY DATA <br />As with surface water, a detailed analysis of TDS concentrations was not performed with this <br />review. TDS concentrations in the alluvium of receiving waters below the Colowyo Mine are a <br />potential issue that will be addressed by the Division and Tri-State in the near future. <br />Groundwater data from down gradient wells was compared to CDPHE's Regulation 41 standards <br />and, as needed, up -gradient well data. As noted in the section above for surface water, the <br />review of the DWR database included wells, and no water supply designations were found. <br />Therefore the review focused on Agricultural Standards rather than water supply standards. <br />Regulation 41 indicates that the standard for dissolved manganese is only appropriate when <br />irrigation water is applied to soils with a pH value lower than 6.0. The Division determined that <br />soils in the area below the Colowyo Mine that are likely to be irrigated with mining -impacted <br />water are not acidic. This was based on an assessment of the Natural Resources Conservation <br />Service (NRCS) Web Soil Survey, including maps and data for slopes, soil pH, and soil depth. <br />The Agricultural Standard in Regulation 41 for dissolved lead is 0.1 mg/l, but the majority of <br />reported values from the monitoring wells at the Colowyo Mine is 0.2 mg/1. This is problematic, <br />and Tri-State should consider using a laboratory method with a lower detection limit or <br />explain to the Division why this is not feasible. The laboratory method for lead was briefly <br />