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CMC—Henderson Operations <br /> DRMS 2021 Annual Water Monitoring Report <br /> May 2022 <br /> Tabular data for MNGW-1, along with applicable NPLs, is presented in Table 1. Accompanying <br /> graphs are provided in Trend Evaluations 1-4. <br /> 2.1.2 Surface Water Sampling Location: BG-20 <br /> BG-20 is located upgradient of the Henderson Mine in Butler Gulch and serves as an indicator of <br /> background surface water quality. A slightly increasing trend in specific conductivity and sulfate <br /> will continue to be monitored despite being insignificant. <br /> Tabular data for BG-20 are presented in Table 1 with accompanying Trend Evaluations 5-8. <br /> 2.1.3 Surface Water Sampling Location: CC-10 <br /> CC-10 is also located upgradient of the Henderson Mine in the West Fork of Clear Creek and <br /> serves as another indicator of background surface water quality. No apparent trends or anomalies <br /> were observed in 2021. <br /> Tabular data for CC-10 are presented in Table 1 with accompanying Trend Evaluations 9-12. <br /> 2.1.4 Surface Water Sampling Location: CC-30 <br /> CC-30 is located downgradient of the Henderson Mine in the West Fork of Clear Creek. Dissolved <br /> manganese and dissolved zinc on 5/20/19 were determined to be outliers using Rosner's statistical <br /> method. Similar concentrations observed in Spring 2020 suggest this trend needs to continue to be <br /> monitored. However, increased concentrations were not observed during Spring sampling in 2021. <br /> Tabular data for CC-30 are presented in Table 1 with accompanying Trend Evaluations 13-16 <br /> 2.2 Henderson Mill <br /> The Henderson Mill monitoring locations include POC wells MLGW-7, MLGW-ACR, MLGW- <br /> 15, and MLGW-17, as well as non-POC surface water locations WFR-20 and WFR-40. Graphical <br /> trends are presented as Trend Evaluations 17-40 of this report. <br /> 2.2.1 Point of Compliance Sampling Location: MLGW-7 <br /> MLGW-7 is a shallow alluvial well nested with MLGW-15 located downgradient of 1-Dam. <br /> Henderson continues to observe an overall decreasing trend in sulfate and specific conductivity. <br /> No other apparent trends, deviations, or exceedances were observed in 2021. <br /> Tabular data for MLGW-7 along with applicable NPLs are presented in Table 2. Accompanying <br /> graphs are provided in Trend Evaluations 17-20. <br /> 2.2.2 Proposed Point of Compliance Sampling Location: MLGW-15 <br /> MLGW-15 is a deeper well nested with MLGW-7 located just downgradient of 1-Dam. Similar to <br /> MLGW-7, slight decreasing trends are observed in specific conductivity and sulfate. No other <br /> apparent trends, deviations, or exceedances were observed in 2021. <br /> Tabular data for MLGW-15 along with applicable NPLs are presented in Table 2. Accompanying <br /> graphs are provided in Trend Evaluations 21-24. <br /> 5 of 8 <br />