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~ ~ III IIIIIIIIIIIII III <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Department of Nalu ral Resources <br />I t I i Sherman SL. Room 215 <br />Denier. Colorado 80203 <br />Phone (3031 865 3567 <br />FAX. (3071 83?-A 106 <br />January 20, 2000 <br />DIVISION OF <br />MINERALS <br />GEOLOGY <br />RECLAMATION <br />MINING•SAFETY <br />Mr. Mike Refer eal ovens <br />CAMAS Co. Inc. e°~ef°°` <br /> <br />7108-M South Alton Way Creg E. \Nalcher <br />Execmive D~reaor <br />Englewood, CO 80112 Michael a L°nF <br /> Divhmn Direuor <br />RE: Technical Adequacy Review of Slope Stability Analysis for New 1 l2 Reclamation Permit <br />Application, Permit No. #M-99-098, Riverview Resources <br />Dear Mr. Refer, <br />This letter is being written address technical issues in the Slope Stability Analysis submitted <br />January 12, 2000, for the new 1 l2 application submitted by your company, Permit No. #M-99- <br />098, Riverview Resources Pit. These issues must be resolved before the Division of Minerals <br />and Geology (DMG) can approve this application. However, this is only a preliminary review of <br />this slope stability analysis, pending the submittal of a full analysis of the hydrological concems <br />detailed in the Technical Adequacy Review dated December 16, 1999. Specifically, items 3, 5, <br />and 6 of the main DMG review, and items 1, 2b, 7, 8 and 9 in Tom Schreiner's review must be <br />addressed before any final determination regarding slope stability at the site can be made. Please <br />address the following concerns prior to the due date of February 4, 2000. <br />l) The presence of de-watering trenches was not included in any of the case analyses. Since the <br />presence of water at the toe of the excavated slopes could effect the phreatic surface within <br />the mined areas, this must be included in all cases. <br />2) The 0.5-foot to 3-foot thick weathered claystone layer directly above the claystone bedrock <br />was omitted from all analyses, and must be included. The soil boring logs indicate that the <br />average thickness of this layer on the west side of the site is 0.7 feet, and that an average of <br />1.6 feet is present on the east side of the site. Analyses should be done for the maximum <br />thicknesses as well as the average values of these layers, assuming zero cohesion and <br />detailing the appropriate effective friction angles and strength values. <br />3) The reference source used to determine the assumed strength values, angles of intemal <br />friction, and cohesion values for the soils used in this analysis is not clear, because the soils <br />are not classified under standard ASTM labels. Please submit the name of the reference work <br />from which these values were obtained, or submit site-specific values from standard soil <br />strength tests done at the site. A lithographic profile of the soils, including wet and dry <br />density, soil composition, intemal friction angles, cohesion, and phreatic surface, is <br />recommended. <br />