2011-09-09_REVISION - M1990057 (3)

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September 1, 2011 The Union Milling Company PO Box 36099 Denver, Colorado 80236 Attention: Mike Elder John Danio Subject: Response to Colorado Division of Reclamation, Mining & Safety Memorandum dated August 12, 2011 Slope Stability Evaluation Tailings Pond Embankment and Future Tailings Slope Union Mill Leadville, Colorado Project No. DN45,584 -130 CTL I THOMPSON CTLIThompson, Inc. analyzed the stability of the proposed Union Milling Company tailings pond embankment and approximate future tailings slope and presented initial results in a letter dated July 8, 2011. We subsequently performed additional testing and analysis, and presented supplemental results in a letter dated August 17, 2011. On August 30, you provided a copy of a Colorado Division of Reclamation, Mining and Safety Memorandum from Tim Cazier, P.E. to Michael Cunningham which contains comments regarding our July 8 letter. The purpose of this letter is to address those comments. For clarity, we have numbered our response consistent with the Memorandum. 1. The clay liner permeability units stated in our letter should have been centimeters /second. The specified permeability is 1x10 cm /sec. 2. The stockpile was sampled so that we could include particles larger than those which were obtained during drilling. We consider the stockpile samples to be representative of both the native soils and the materials which will be used to construct the embankment. 3. The site was covered with snow at the time of our field investigation in May and spring melt was in progress. There was a pool of water in the pond adjacent to the exploratory boring. The water found in our boring may be indicative of temporary perched water conditions which develop during snowmelt and the influence of the water within the existing, unlined pond, rather than the "aquifer." In 1995, we drilled an observation hole south of the existing pond and found no water to approximate elevation 9685, or about 9 feet below the proposed excavation level (see Appendix C of July 8 letter). 4. The cyclone tailings will be placed on top of the man -made liner on the inside face of the embankment. We differentiated between cyclone sands and slime in our initial stability analysis because we thought the materials would have slightly differing strength properties. At that time, our direct shear 1971 West 12th Avenue 1 Denver, Colorado 802041 Telephone: 303 - 825 -0777 Fax: 303 - 825 -4252