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Zach Trujillo 2 May 4, 2012 <br />Purgatoire River flood plain, as illustrated in Figure 1 of the report. The ground <br />elevation (as indicated on the boring log headers) at BH -40 is 7,626.2 ft and the ground <br />elevation at BH -41 is 7,620.3 ft. The elevation to which each of these two borings was <br />advanced was approximately 7,604.7 ft and 7,599.8 ft, respectively. The top of bedrock <br />elevation, as determined from each of these borings, is approximately 7,603 ft and <br />7,610 ft, respectively. Neither of these borings encountered alluvial groundwater that <br />could be confined above the bedrock surface nor was any groundwater encountered <br />within the shallow depths of the bedrock that was penetrated. <br />Based on this information, alluvial groundwater was not encountered at the locations <br />and depths explored. In addition, groundwater that could be associated with a confined <br />condition within the bedrock was not encountered at the locations and depths explored. <br />However, to account for a possible increase in groundwater conditions, each of the three <br />slope stability geometries considered, 2.0(H):1.0(V), 2.5(H):1.0(V) and 3.0(H):1.0(V), <br />were analyzed both with groundwater present and with no groundwater present. The <br />analyses with groundwater present included a groundwater surface at elevation 7,613 ft. <br />Considering a groundwater level to elevation 7,613 ft accounts for an increase in <br />groundwater by anywhere from 8 to 13 ft, based on the total depth of the borings or <br />from 3 to 10 ft, based on the possibility of groundwater confined to the alluvium on top <br />of the bedrock surface. <br />As a result of the slope stability analysis, which included cases both with and without <br />groundwater, the presence of groundwater had no effect on the stability of the <br />Development Waste Disposal Area (DWDA) pile. The results of the slope stability <br />analysis are summarized in Table 6 of our report and are presented below for reference. <br />It is our opinion that the increase in groundwater levels considered in our slope stability <br />analysis conservatively account for possible seasonal fluctuations that may occur in <br />proximity to the West Portal Waste Rock Disposal Area and meet the DRMS <br />requirements of item 2, listed above. <br />Table 6. Stability Factors for Various Slope Conditions <br />Side Slope Stability <br />Case Configuration Depth to Groundwater Factor <br />(H:V) (ft) <br />1 2:1 Not present 1.2 <br />2 2.5:1 Not present 1.5 <br />3 3:1 Not present 1.7 <br />4 2:1 3 ft above bedrock at embankment toe (elev. 7,613 ft) 1.2 <br />5 2.5:1 3 ft above bedrock at embankment toe (elev. 7,613 ft) 1.4 <br />6 3:1 3 ft above bedrock at embankment toe (elev. 7,613 ft) 1.7 <br />