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STABILITY ANALYSIS <br />We performed stability analyses to assess the mass stability of the existing and proposed <br />refuse configurations. We understand a minimum factor of safely of 1.5 is required for this facility <br />according to Regulations of the Colorado Mine land Reclamation Board for Coal Mining (1980, revised <br />January 17, 1990). Wyoming Fuel Company personnel provided us with plans and topography of the <br />existing refuse and the proposed pile (Fig. 3). The fill is planned with 2:1 slopes with 20 foot horizontal <br />benches every 50 feet of vertical rise. From these plans and our field investigation we constructed a <br />profile of the fill which we used for our stability analysis. <br />Characteristics of Materials <br />The characteristics of the refuse material used in stability analyses were based upon our field <br />and laboratory testing. In our opinion, the refuse is a slightly cohesive soil which is very sandy. We <br />do not think that the refuse is without cohesion and therefore do not believe this to be an infinite slope <br />stability problem. <br />During drilling we found the upper 20 feet of the refuse to be very wet, whereas the deeper <br />refuse was dryer and stiffer. We believe there is "perched" water in the fill which is draining relatively <br />slowly. In our analyses of the existing pile, we modeled a wet layer within the profile which extended <br />from 3 teet below the surface to a depth of 25 feet. <br />The measured cohesion of the refuse ranged from 500 to B00 psf, We used a base value of <br />400 pounds per square foot for cohesive strength. The measured friction angle of the material ranged <br />from 30 to 35 degrees. We used a base value of 30 degrees. The density of the material was <br />estimated based upon the average of the density testing which was performed. Density of 90 pcf was <br />assumed for "dry" materials and 120 pcf for the 'wet" layer. Parametric studies were performed to <br />evaluate the effects of varying cohesion, friction and density upon stability. <br />7 <br />