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CMC—Henderson Operations <br /> 5-Quarter Water Quality Data and Baseline Parameters Report <br /> May 2014 <br /> 1 1.0 Introduction and Background <br /> The Henderson Operations Groundwater Management Plan (GWMP), submitted as Technical Revision <br /> 16 (TR-16) to the Henderson Mine and Mill Reclamation Permit M-1977-342 was approved on July 25, <br /> 2012. The GWMP provided that Henderson would conduct further groundwater studies at the Henderson <br /> Mill to determine the appropriateness of current point of compliance (POC) locations as well as the <br /> potential for establishing new POC locations below 1-Dam and in the Potato Gulch drainage. <br /> ' Additionally, the GWMP provided that Henderson would collect and submit the results of baseline <br /> parameters and Numeric Protection Level (NPL) assessments for new POC locations. This report has <br /> been prepared to provide groundwater study results as well as the results of the baseline parameters and <br /> ' NPL assessments for new POC locations. <br /> ' 2.0 Groundwater Studies <br /> An initial Groundwater Monitoring Point of Compliance (POC) Technical Memorandum (AJAX and <br /> Clear Creek Associates,2013)was prepared and submitted to the DRMS in May 2013. The Memorandum <br /> presented several preliminary recommendations, including completion of additional monitoring to <br /> provide data to support fmal determinations on potential POC locations, particularly below 3-Dam. A <br /> 1 subsequent Groundwater Monitoring Point of Compliance Update Memorandum(AJAX and Clear Creek <br /> Associates, 2014a) has been prepared and is being submitted with this report(Appendix A). Collectively, <br /> 1 the memorandums recommend that POC locations be established at MLGW-15 and MLGW-17. These <br /> POC locations are in addition to existing GWMP approved POC locations MLGW-7 and MLGW-ACR. <br /> 3.0 Baseline Parameters and NPL Assessments <br /> ' The purpose of this section is to provide the results of baseline parameters monitoring and related NPL <br /> assessments for existing POC location MLGW-ACR and the new proposed POC locations MLGW-15 <br /> and MLGW-17. Figures 1 — 3 of Appendix A illustrate the location and geographic setting of the <br /> Henderson Mill,including POC locations. <br /> ' 3.1 MLGW-ACR <br /> 3.1.1 Monitoring Summary <br /> MLGW-ACR was established in the GWMP as the POC for water supply related parameters since it <br /> represents the nearest location of actual potable water use to the Henderson Mill facility (see Section <br /> ' 3.2.6.1 of the GWMP for additional information). However, when the GWMP was approved, there was <br /> insufficient data to establish NPLs. Therefore, as required by the GWMP, baseline monitoring was <br /> ' Page 2 of 9 <br />