2013-01-15_REVISION - M1977342 - Laserfiche WebLink

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.A11 Mr. Miguel Hamarat Climax Molybdenum Company — Henderson Operations 1746 County Road 202 Empire, Colorado 80438 Subject: Henderson Mill 1 -Dam Wellfield Project - Technical Revision 10 (TR -10) Assessment, Henderson Mill, Permit No. M -77342 Dear Mr. Hamarat: 1 CLEAR CREEK --"Ow ASSOCIATES ianuary 3, 2013 Transmitted by E -mail AJAX Mountain Enterprises LLC (dba AJAX Ltd) and Clear Creek Associates PLC (Clear Creek) have reviewed the TR -10 submittal (FR-10), dated May 15, 2001, and assessed the requirements of TR -10 relative to monitor well installation and monitoring activities completed since 2001. Per TR -10 Task 1 - Drill Test Holes and Site Extraction Wells and Task 2 - Design Extraction Well System, several test holes and extraction wells have been installed according to the proposed design. The TR -10 Scope of Work (SOW) proposed to drill up to fourteen (14) test holes along the proposed extraction well system alignment. The information obtained from test hole /piezometer installation would be used to select the most advantageous sites for extraction wells and to develop the extraction well system design. It was estimated that seven (7) sites would be selected for extraction well installation. A total of fifteen (15) test holes /piezometers (THP -1 to THP -15) were installed along the 1 -Dam wellfield alignment. They were installed at approximately 50 ft spacing and were completed with 2- inch PVC as specified in the SOW. Three additional piezometers, HMEX -1R, 2R, and 3R, were installed to the east of these test holes and are also paired with extraction wells. A total of nine extraction wells (HMEX -01 to HMEX09) were installed. "Two electric submersible pumps were installed in HMEX -2 and HMEX -3, and these are the two extraction wells currently operating. The remaining seven extraction wells arc outfitted with pneumatic pumps and have operated historically, as needed. The locations of the test holes /piezometers and extraction wells are shown on Figure 1. As noted in the URS letter, dated November 30, 2010, the 'IR -10 SOW specified that up to six more piezometers be installed at strategic locations surrounding the extraction well system. These piezometers were to be used to monitor water levels for evaluation of groundwater capture. The locations were not specified in the TR -10 submittal. URS stated in their 2010 letter that the test hole /piezometers installed adjacent to the extraction wells would not meet the wellfield performance monitoring objective envisioned in TR -10. AJAX and Clear Creek agree that downgradicnt wells in addition to the test hole /piezometers along the 1 -Dam wellfield alignment are necessary to monitor system performance.