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CMC — Henderson Operations <br />DRMS 2014 Annual Water Monitoring Report <br />May 2015 <br />Introduction <br />The GWMP establishes a plan for groundwater monitoring at the Henderson Mine and Mill for <br />the protection of groundwater quality pursuant to Rule 3.1.7(5) of the Mineral Rules and <br />Regulations of the Colorado Mined Land Reclamation Board for Hard Rock, Metal, and <br />Designated Mining Operations and the Colorado Water Quality Control Commission (WQCC) <br />standards. Henderson has prepared this report in accordance with the requirements of Section 7.1 <br />of the GWMP to summarize results of 2014 water monitoring activities. <br />1.0 Discussion of Annual Water Monitoring Data <br />This section provides a summary of the annual water monitoring data collected in 2014 in <br />accordance with the GWMP for each permit -identified POC well and non -POC long-term <br />surface water monitoring location at the Henderson Mine and Mill. Monitoring is conducted <br />three times per year as stipulated in the GWMP as follows: <br />• During the April through June spring run-off period; <br />• During the summer months of July and August; and <br />• During the September through December low -flow period. <br />To provide a better data set for trending purposes, the data set generally include historical data <br />from triannual DRMS monitoring and baseline monitoring. Data can be seen in trend evaluation <br />graphs as well as in the data tables. Note that for the purpose of trending the analytical data, <br />results reported below the laboratory detection limit are shown as a value of zero. All monitoring <br />locations are depicted in Figures 1 and 2. <br />Outliers are identified, as needed, using either the Dixon's or Rosner's statistical method <br />depending on the available number of data points. Although data from prior reporting years is <br />presented herein for trending and discussion purposes, outlier and NPL assessments/discussions <br />are limited to current reporting year data. <br />2.1 Henderson Mine <br />Henderson Mine monitoring locations include POC well MNGW-1 and surface water locations <br />BG -20, CC -10 and CC -30. Two new groundwater wells were installed in 2014 to help with <br />ongoing groundwater quality assessments and identified as MNGW-3 and MNGW-4. <br />Graphical trends for MNGW-1, BG -20, CC -10 and CC -30 are presented as Trend Evaluations 1- <br />16 of this report. <br />2.1.1 Point of Compliance Sampling Location: MNGW-1 <br />A deviation from the pH NPL of 6.5 - 8.5 was observed at the Mine POC well MNGW-1 on May <br />27, 2014 with a measured value of 6.4 standard units (s.u.). A follow-up sample was collected on <br />June 21, 2014 with a measured value of 8.0 s.u., within the acceptable NPL range. As mentioned <br />in the Executive Summary, a groundwater quality investigation at MNGW-1 has been ongoing <br />with the latest update regarding installation of new monitoring wells provided in the <br />Groundwater Quality Assessment Update, Technical Memorandum (AJAX and Clear Creek <br />Associates, February 2015). Monthly monitoring being conducted at MNGW-1 for an expanded <br />parameter set as part of ongoing groundwater quality assessments concluded at the end of 2014. <br />4 of 7 <br />