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
Introduction
The GWMP establishes a plan for groundwater monitoring at the Henderson Mine and Mill for the
protection of groundwater quality pursuant to Rule 3.1.7(5) of the Mineral Rules and Regulations
of the Colorado Mined Land Reclamation Board for Hard Rock, Metal, and Designated Mining
Operations and the Colorado Water Quality Control Commission (WQCC) standards. Henderson
has prepared this report in accordance with the requirements of Section 7.1 of the GWMP to
summarize results of 2020 water monitoring activities.
1.0 Discussion of Annual Water Monitoring Data
This section provides a summary of the annual water monitoring data collected in 2020 in
accordance with the GWMP for each permit-identified POC well and non-POC long-term surface
water monitoring location at the Henderson Mine and Mill. Monitoring is conducted three times
per year as stipulated in the GWMP as follows:
• During the April through May spring run-off period;
• . During the summer months of July and August; and
• During the September through December low-flow period.
To provide a better data set for trending purposes,the 2020 water quality data has been appended
to the previous six years of data. This data can be seen in trend evaluation graphs as well as in the
data tables. Note that for trending the analytical data, results reported below the laboratory
detection limit are shown as a value of zero.All monitoring locations are depicted in Figures 1 and
2.
Outliers are identified, as needed, using either the Dixon's or the Rosner's statistical method
depending on the available number of data points. Although data from prior reporting years is
presented herein for trending and discussion purposes, outlier and NPL assessments/discussions
are limited to current reporting year data.
2.1 Henderson Mine
Henderson Mine monitoring locations include POC well MNGW-1 and surface water locations
BG-20, CC-10 and CC-30. Graphical trends for MNGW-1, BG-20, CC-10 and CC-30 are
presented as Trend Evaluations 1-16 of this report.
2.1.1 Point of Compliance Sampling Location: MNGW-1
MNGW-1 is a shallow alluvial well located downgradient of the Henderson Mine operations.
Values of pH below the established NPLs were seen during monitoring events in 2020: 6.3
standard units (s.u.) on 5/14/20, 6.0 s.u. on 8/20/20, and 6.2 s.u. on 12/14/20. In accordance with
the GWMP,Henderson has provided notification to the DRMS upon reoccurring pH exceedances
for POC wells,when necessary.
Slightly increasing trends in dissolved zinc, continued to be monitored and those trends were
confirmed with the 2020 data as well. While not significant, and with respect to dissolved zinc
well below the NPL,this trend will continue to be monitored.
Tabular data for MNGW-1, along with applicable NPLs, is presented in Table 1. Accompanying
graphs are provided in Trend Evaluations 1-4.
2of5