2021-06-02_HYDROLOGY - M1977342 ‎(2)‎

• Permit No: M1977342
• IBM Index Class Name: HYDROLOGY
• Doc Date: 6/2/2021
• Doc Name: Water Monitoring - Groundwater
• From: Climax Molybdenum
• To: DRMS
• Email Name: PSH
• Media Type: D
• Archive: No

CMC—Henderson Operations
DRMS 2020 Annual Water Monitoring Report
May 2021
2.1.2 Surface Water Sampling Location: BG-20
BG-20 is located upgradient of the Henderson Mine in Butler Gulch and serves as an indicator of
background surface water quality. 2020 results indicate a continued increasing trend developing
in specific conductivity and sulfate. While the 2020 results for specific conductivity remain within
historical ranges, the sulfate result from the third trimester indicates an increase relative to
historical data over the past six years. It should be noted that the difference between this result and
the next highest value over the past six years is only 5.4 mg/L and the scale exaggerates this
difference.Nevertheless, this will continue to be monitored following future Triannual events.
Tabular data for BG-20 are presented in Table 1 with accompanying Trend Evaluations 5-8.
2.1.3 Surface Water Sampling Location: CC-10
CC-10 is also located upgradient of the Henderson Mine in the West Fork of Clear Creek and
serves as another indicator of background surface water quality. An increase in dissolved iron and
zinc concentrations during the spring run-off periods is observed and will continue to be
monitored. Like BG-20, specific conductivity and sulfate concentrations indicate slightly
increasing trends and will continue to be monitored.
Tabular data for CC-10 are presented in Table 1 with accompanying Trend Evaluations 9-12.
2.1.4 Surface Water Sampling Location: CC-30
CC-30 is located downgradient of the Henderson Mine in the West Fork of Clear Creek.Dissolved
manganese and dissolved zinc on 5/20/19 were determined to be outliers using Rosner's statistical
method. With the inclusion of 2020 results, there appears to be a developing trend of increasing
concentrations of dissolved iron,manganese, and zinc. This trend will continue to be monitored in
addition to performing statistical analyses following future sampling events.
Tabular data for CC-30 are presented in Table 1 with accompanying Trend Evaluations 13-16
2.2 Henderson Mill
The Henderson Mill monitoring locations include POC wells MLGW-7 and MLGW-ACR, non-
POC wells MLGW-15, and MLGW-17, as well as non-POC surface water locations WFR-20 and
WFR-40. Graphical trends are presented as Trend Evaluations 17-40 of this report.
2.2.1 Point of Compliance Sampling Location: MLGW-7
MLGW-7 is a shallow alluvial well paired with MLGW-15 located downgradient of 1-Dam.
Henderson continues to note a slight decreasing trend in sulfate and specific conductivity.
Tabular data for MLGW-7 along with applicable NPLs are presented in Table 2. Accompanying
graphs are provided in Trend Evaluations 17-20.
2.2.2 Proposed Point of Compliance Sampling Location: MLGW-15
MLGW-15 is a deeper well paired with MLGW-7 located just downgradient of 1-Dam. Similar to
MLGW-7, slight decreasing trends are observed for specific conductivity and sulfate.
Tabular data for MLGW-15 along with applicable NPLs are presented in Table 2. Accompanying
graphs are provided in Trend Evaluations 21-24.
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