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4`Y' W.W. ENTERPRISES Consulting Engineering <br />2115 9th Street, P.O. Box 1242, Limon, Colorado 80828 (719) 775-9314 <br />VMV <br />June 7, 2010 <br />Project No. 09-1214 0 <br />Mr. Michael A. Cunningham <UN 0 9 2010 <br />Environmental Protection Specialist p ai Roc n, <br />Division of Reclamation, Mining, and Safety and SW" <br />Colorado Department of Natural Resources <br />1313 Sherman Street, Room 215 <br />Denver, CO 80203 <br />RE: Dill Pit; DRMS File No. M-2009-077; Slope Stability Analysis <br />Dear Mr. Cunningham; <br />Enclosed are drawings indicating the excavation for the proposed Dill Pit in Elbert <br />County, Colorado. A Site Plan with cross sections are included. <br />The start of the excavation of minerals is proposed to start at a point no closer <br />than 25-feet from the East Right-of-Way and 39-feet from the edge of the road base of <br />County Road 189. From this excavation point, minerals will be mined down at a <br />maximum 4 to 1 slope to the East until a minimum 2-feet above groundwater. For this <br />site, the maximum depths excavated will be 10 to 25-feet. <br />Soils on the site are predominantly classified as SP-SM with some SP and SM <br />found. The maximum slope for cuts in cohesionless sand is the angle of internal friction, <br />also know as the angle of repose. For these type of soils the angle of internal friction will <br />range from 30 to 37 degrees according to Peck, et al. and Meyherfhof. Inspection shows <br />that the slope of the internal friction angle of the on-site soils is greater than the final 4 to <br />1 slope, giving a minimum safety factor SF = friction angle / 4:1 slope = 34 degrees/ 14.0 <br />degrees = 2.4. <br />Please contact our office, if you have any questions concerning this information. <br />Respectfully; <br />enclosures