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,... <br />iii iiiiiiiiiiiiiiii <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Depanmenl of Natural Resources <br />1313 Sherman St., Room 215 r <br /> <br />Denver, Colorado 80203 I <br />~~~ <br /> <br />Phone: 13031 866-3567 I <br />FAX: 13011872-8106 <br /> DEPARTMENT OF <br /> NATURAL <br />DATE: January 10, 1997 RESOURCES <br /> Roy Romer <br /> Governor <br />Bill Carter <br />TO IamesS Lochhead <br />. Execmrve Director <br />_ Michael B. Long <br /> Drvrsion Director <br />FROM: Jim Pendleton <br />RE: "Coal Mine~Vif~e Bank Design for the Sanborn <br />Creek Mine" (Permit No: C-81-022) <br />I have completed a preliminary review of the geotechnical aspects of the <br />design analysis prepared for Oxbow by WESTEC, which you forwarded to <br />my attention. During our visit to the proposed waste pile site last fall, I <br />indicated my willingness to prefiminarify review the document, in an <br />effort to expedite the process. <br />Design Report & Stability Analysis <br />WESTEC has done a good job of preparing the design documents and the <br />accompanying stability analysis. A combination of laboratory analysis and <br />field blow count conversion was used to develop material strength <br />properties for the waste and three materials encountered within the site <br />foundation. All of the analytical techniques and field observations appear <br />appropriate. The stability analyses, performed for both rotational and <br />planar failure scenarios project a minimum static slope safety factor of <br />2.1 for the circular failure mode and 2.3 for planar failure. Corresponding <br />pseudo static factors of safety are 1.5 for the circular case and 1.8 for <br />the planar case. As such these safety factors easily satisfy the <br />requirements of our regulations. <br />My review of the design report and analysis discerned only one concern. <br />During our reconnaissance of the site last fall, I mentioned a concern <br />