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DIVISION OF RECLAMATION, MINING AND SAFETY <br />Department of Natural Resources <br />1313 Sherman St., Room 215 <br />Denver, Colorado 80203 <br />Phone: (303) 866 -3567 <br />FAX: (303) 832 -8106 <br />August 16, 2013 <br />Mr. Todd Yee <br />AT Consulting, INC. <br />305 Denver Avenue, Suite D <br />Fort Lupton, CO 80621 <br />RE: West Farm Pit, DRMS File No. M -2008 -078 <br />Technical Revision TR -02 <br />Preliminary Adequacy Review <br />Dear Mr. Yee: <br />STATE OF COLORADO <br />COLORADO <br />D I V I S I O N OF <br />RECLAMATION <br />MINING <br />SAFETY <br />John W. Hickenlooper <br />Govemor <br />Mike King <br />Executive Director <br />Loretta E. Pineda <br />Director <br />The Division has completed a review of the technical revision, and has the following comments: <br />1) Will there be any monitoring of the groundwater levels outside of the slurry wall? <br />2) Please provide a statement clarifying how the operator will notify the Division of Reclamation, <br />Mining and Safety (Division) of the results of the State Engineers leak test. <br />3) Please provide a statement clarifying when and how the operator will notify the Division of their <br />progress into a new mining phase. <br />4) No stability cross - sections, section locations, or data runs from the analysis were included in the <br />report. It is difficult to fully understand the geometry of the section being analyzed and the <br />subsurface characteristics being evaluated without this data. Please provide a cross section <br />location map, cross sections, and evaluation data for this analysis. <br />5) One area of concern for analysis is the area between the two pits, both during and after mining <br />operations. Please provide discussion regarding the potential stability issues for mining both <br />sides of this road and utility corridor. <br />6) The trenching system being proposed for the slurry wall installation will use a one -pass trencher <br />method to construct a slurry wall approximately 18 inches thick and a minimum of 3 feet into <br />"unweathered bedrock ". Of the seven borings drilled on the site, all but one boring indicated <br />that slightly weathered bedrock was encountered to the total depth of the hole. Please provide <br />the criteria for determining the surface of "unweathered bedrock" for the slurry wall anchor <br />depth. <br />7) The water level used in the analysis is stated as being at an elevation located at the top of the <br />gravel /sand layer" for the analysis. The borehole logs indicate the water level (August 2010) is <br />approximately 7 -15 feet below the ground surface, in some cases several feet above the top of <br />Office of Office of <br />Mined Land Reclamation Denver - Grand Junction - Durango Active and Inactive Mines <br />