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• Stability Analysis <br />See various Geotechnical Engineering Studies performed by Lambert and <br />Associates and Buckhorn Geotech for the Bowie No. 2 Mine, Gob Piles 2 & 4, <br />following this section. <br />Lambert's report dated November 10, 2003, determined the 230 -foot high coal <br />mine waste disposal area would be stable with 2:1 slopes, horizontal to vertical, <br />with15 foot wide terraces on 50 foot intervals. The stability analysis was not <br />performed with strength parameters from the wash plant refuse because the <br />wash plant was not operating at the time. Therefore, the DRMS placed <br />stipulation number 16 in the permit that required the Operator to determine site <br />specific strength parameters of the coal processing waste and demonstrate the <br />proposed fill, as approved, will be stable with a minimum factor of safety of 1.5. <br />Lambert's report dated March 17, 2005, which follows this section, explains they <br />developed representative site specific strength parameters for the in -place coal <br />processing waste. Their stability analysis performed with the site specific <br />• strength parameters indicates the pile will be stable (1.5 FS) if the slope face <br />inclinations are flattened to 5:1. The stability analysis was run with the first 50 <br />foot in place with a 2.5:1 slope. The Operator flattened the face inclinations as <br />required to achieve the required 1.5 factor of safety. <br />The stability analysis for the west expansion of the gob pile follows this section. <br />It was prepared by Buckhorn Geotech, dated February 1, 2007 and is titled <br />Geotechnical Report, Stability Evaluation of Coal Waste Pile No. 4, Delta <br />County, Colorado. <br />Buckhorn Geotech's report dated September 22, 2008 which follows this section <br />provides an updated stability evaluation of coal mine waste pile number 2. This <br />report concludes the pile will be stable with slopes no steeper than 3h:1 v with 15' <br />wide terraces on 50' intervals with the first 50 foot sloped no steeper than <br />2.5h:1 v. <br />Buckhorn Geotech's stability revised analysis for the west expansion follows this <br />section. It was prepared May 18, 2009 and is based on the parameters <br />• determined in the original report dated February 1, 2007. The revised report <br />TR -64 -13- 09/09 <br />AfPRov� <br />i z q <br />