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GbMi f'-~5 5 r5 f <br />ap <br />INTEROFFICE MEMORANDUM <br />COLORADO DIVISION OF MINERALS AND GEOLOGY <br />13]3 Shetman St., Rm. 215 <br />Denvet, CO 80203 <br />TO: Gregg R. Squire <br />FROM: Kathleen L, Sullivan, P.E. ~~.-~~~~.~~ <br />SUBJECT: M-2000-016, Lafarge West, Inc.: Riverbend Operation, AM 01 <br />~ Adequacy Review No. 5 <br />DATE: July 26, 2005 <br />CC: Carl Mount, DMG (via e-mail); Kate Pickford, DMG (via a-mail) <br />This memo contains adequacy review comments to the applicant's July 12, 2005 (Third) <br />adequacy responses to the Division's geotechnical review of the Lafarge West, Inc.: <br />Riverbend Operation 112(c) Amendment (AM-01) Application, File No. M-2000-016. <br />I have directed my comments to the applicant. The applicant may contact me with any <br />questions at (303) 866-4060. <br />Rule 6.5 Geotechnical Stability Exhibit <br />The setback recalculated for Phase 5, Cell 5 - N,E,S (Figure 18) apparently was not <br />based upon the critical failure surface. Using the material depths, phreatic surface, and <br />same slope as employed by the applicant's consultant, WSI Weiland, Inc., the 110.5-feet <br />setback yielded a factor of safety of 0.93. For a factor of safety of 1.0, a 120.5-feet <br />setback from top of slope and 149 feet from the toe is necessary. Please modify all <br />related maps and documents to reflect the minimum 120.5-feet setback. <br />2. The Mine Plan maps still show some setbacks inconsistent with the geotechnical stability <br />analysis. For example, for Phase 5, Cell 5 - N,E,S discussed above, some setbacks <br />along the north, east, and south cell walls are still shown as 69 feet. Some setbacks are <br />not shown, such as the 50-feet for Phase 5, Cell 5 - W. The applicant must modify the <br />Mine Plan maps to reflect setbacks greater than or equal to those prescribed by the <br />slope stability analyses. <br />