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Henderson Mine and Mill <br />Geochemical Evaluation and Sampling Plan <br />Introduction <br />The Henderson Mine and Mill (Henderson) is currently in the process of revising <br />Technical Revision 05 (TR-05) to formally establish a ground water protection program <br />under its Reclamation Permit Number M-77-342. As part of this process, Henderson is <br />completing a geochemical evaluation to identify analytes associated with site operations <br />that should be periodically monitored and subject to numeric limits. This Geochemical <br />Evaluation and Sampling Plan (Plan) summarizes the proposed sampling plan and <br />parameters to be tested. <br />Henderson has performed a significant amount of surface and ground water quality <br />monitoring for a variety of parameters including cadmium, copper, lead, zinc, iron, <br />manganese, mercury, silver, pH, and temperature. This Sampling Plan will include these <br />and other parameters established by the State Water Quality Control Commission. The <br />intent is to identify those parameters that have a reasonable potential of being transported <br />from mining materials to surface and ground water systems. The complete list of <br />parameters to be analyzed is included in Attachment 3. <br />Determination of Sampling Locations <br />Three sampling points have been selected for this project, two at the Mine and one at the <br />Mill. Maps of the respective areas identifying the sampling points are included as the <br />following attachments. <br />• Attachment 1 - Displays the entire mine area and the two sampling locations. <br />• Attachment la - Identifies the first sampling location at the Mine (Location #1), <br />which is at the northeast end of the mine site, just down-gradient of the Emrick <br />and Hill industrial area. This area appears to contain materials displaying elevated <br />levels of mineralization. This area is considered a worst-case scenario sampling <br />location for identifying material with contamination potential. <br />• Attachment lb -Identifies the second sampling location at the Mine (Location <br />#2), which is located generally in the central part of the mine site, north of the <br />surface impoundments. We believe this location will provide samples that are <br />more representative of general site geology than Location #1. <br />• Attachment 2 - Mill Site Map - Displays the entire mill area and the single <br />sampling location. <br />Version 1, May-2010 Page 1