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CMC — Henderson Operations <br />DRMS Annual Water Monitoring Report <br />May 2013 <br />1.0 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 2012 water monitoring activities. <br />2.0 Baseline Monitoring <br />Baseline monitoring is being performed in several locations including groundwater wells <br />MLGW -17 and MLGW -18 below 3 -Dam, MLGW -15 nested with POC well MLGW -7 and the <br />designated domestic water supply POC well MLGW -ACR. Pursuant to the GWMP, newly <br />monitored or constructed groundwater monitoring locations shall be monitored for a minimum of <br />five quarters for the baseline parameters summarized in Section 4.2 of the GWMP. <br />At this time, Henderson is in the midst of the five quarterly monitoring events at all of these <br />locations. Following completion of the five quarterly monitoring events for each well, a <br />summary of the baseline dataset will be provided to the DRMS as required by the GWMP. <br />3.0 Discussion of Annual Water Monitoring Data <br />This section provides a summary of the annual water monitoring data collected in 2012 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 />It should be noted that a spring run -off period sample was not collected in 2012 as the GWMP <br />was not approved until July 2012. <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. Monitoring locations are depicted in Figures 1 <br />and 2. <br />3.1 Henderson Mine <br />Henderson Mine monitoring locations include POC well MNGW -1 and surface water locations <br />BG -20, CC -10 and CC -30. Graphical trends are presented as Trend Evaluations 1 -16 of this <br />report. Note that for the purpose of trending the analytical data, results reported below the <br />laboratory detection limit were included as a value of zero. <br />3.1.1 Point of Compliance Sampling Location: MNGW -1 <br />A pH deviation measuring 6.4 was observed (NPL of 6.5 - 8.5) during the December 2012 <br />monitoring event. This appears to be attributable to normal seasonal fluctuations /low flow winter <br />3 of 5 <br />