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• located on the three lower benches. The information available indicates the drain <br />system is functioning in the lower portion of the fill. <br />Earthquake. Liquefaction of the coal refuse or soil is not considered a risk. <br />A pseudo-static analysis was performed using horizontal accelerations of 0.05, 0.10 <br />and 0.15 g. The 0.1 coefficient is considered appropriate for areas of moderate <br />seismicity, including Colorado. <br />Results of Stability Analysis <br />The results of the parametric analysis are shown on Fig. 7. Overall the <br />calculated results indicate the existing and proposed configurations possess <br />adequate factors of safety, even considering unfavorable strength, water conditions <br />and earthquake conditions. A factor of safety of 1.9 was calculated for the existing <br />• RDA configuration, even with the worst-case water condition the factor of safety was <br />1.5. Using apseudo-static coefficient of 0.1 g, a factor of safety over 1.4 was <br />calculated for the existing RDA. <br />We first analyzed RDA configurations with 2.0:1 and 2.5:1 (horizontal:vertical) <br />slopes between benches. The RDA configuration was then finalized and we analyzed <br />2.2:1 slopes with a maximum elevation of 8035 feet. <br />The steeper proposed RDA configuration (with 2:1 slopes between benches) <br />has lower factors of safety for all conditions modelled compared to the 2.5:1 <br />configuration. For the worst case strength and unk weights considered, the 2:1 <br />configuration has satisfactory factors of safety above 1.5. The only exception was <br />for a coal refuse strength of 30 degrees with no cohesion where the factor of safety <br />was 1.4. <br />• <br />20 <br />