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Mr. Henry Barbe <br />March 8, 1994 <br />Page 2 <br />Geologic Setting: The physiographic setting of the two areas are substantially <br />different. The proposed materials storage bench is to be constructed parallel <br />to a bedrock controlled ridge. Bedrock was encountered at 80 to 90 feet below <br />surface in all borings during the drilling investigation program for this azea. <br />In comparison, the main portal access azea was established in a thick colluvial <br />bowl area without bedrock control. <br />Landslide: One aspect of Envirocon's site assessment was to identify and map <br />all past slope instability failures. In the area of the proposed storage bench, <br />hummocky topography, soil slump and vegetation effected by slope failure was <br />not observed. In August 1993, a drilling program was implemented to further <br />investigate the subsoils. The results of the drill program and how they were <br />used in the slope stability analysis will be explained in the groundwater <br />section. <br />Springs: The first phase of Envirocon's West Elk Mine Assessment was to <br />identify springs (the spring season of 1993 was one of the wettest period on <br />record) in the field. In the area of the proposed storage bench, no springs were <br />observed. <br />Groundwater: The August drilling program of four subsurface holes did not <br />encounter groundwater; subsequently, a groundwater table was not <br />incorporated into the stability analysis computer program. Natural moisture <br />contents in clay samples retrieved at five foot intervals ranged from 14 to 18 <br />percent. In the graphs of moisture vs depth (Figures 1 through 4), the highest <br />moisture content was noted at the bottom of the borings just before <br />encountering bedrock. <br />New Stability Analysis <br />The original stability analysis was recalculated with groundwater being <br />incorporated into the model. The first analysis assumed a groundwater table at 70 <br />to 80 feet below the surface. A worst case scenario was also assumed with a water <br />table at 10 feet below the surface. This is an extremely unlikely event due to the low <br />hydraulic conductivity of clay and the lack of springs along the ridge. <br />Results of the new stability analysis (factors of safety) for profiles A through <br />E are summarized in the attached table. A review of the calculated results from the <br />stability analysis program indicate that by imposing a groundwater table at 70 to 80 <br /> <br />