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Boring <br />Number <br />Water Level During Drilling <br />(feet below surface) <br />LH -1 <br />8.3 <br />LH -2 <br />11.6 <br />• <br />Transit Mix <br />May 18, 2011 <br />Page 3 of 3 <br />was approximately 35.4 feet bgs and extended to approximately 40 feet bgs. The material was very soft, highly <br />weathered, and slightly moist with blow counts of 50 for 3 inches of penetration. <br />Clayey Shale and Shale bedrock of the Pierre Shale Formation was encountered beneath the alluvium in boring <br />LH -1 and residuum in boring LH -2. The Pierre Shale was encountered at depths of 35.4 feet and 38.1 feet bgs and <br />extended beyond the bottom of the exploration. The bedrock was slightly moist, with field hardness classification <br />(resistance to abrasion) of very soft. Modified California penetration values ranged from 50 blows per 1 inch to <br />50 blows per 3 inches of penetration. <br />The shale was tested for unconfined compressive strength in boring LH -1. The unconfined compressive strength <br />result was 9,313 psf. The laboratory results are provided in Table I and Appendix B. <br />Groundwater <br />Groundwater was encountered while drilling the borings as tabulated below. Fluctuations in the groundwater <br />level may occur due to variations in rainfall, temperature, site development and other factors not evident at the <br />time measurements were taken. <br />The natural static groundwater is assumed to be approximately 1 feet below existing grade, and during mining <br />Lyman Henn assumes that the phreatic surface will be drawn down by dewatering to the top of the weathered <br />bedrock. <br />ANALYSES <br />Lyman Henn performed an analysis for two separate cross - sections which were provided by Tuttle & Associates <br />(Reference 1). The cross- section identifications used by Lyman Henn (Figure 2) are consistent with the drawings <br />provided by Tuttle & Associates. Section D -D' is located at the eastern pit boundary with the proposed pit wall <br />offset 85 feet from the property line, a 55 -foot drainage ditch is included within the offset distance. Section E -E' <br />is along the northern pit boundary with a proposed 50 -foot offset from the property line. Lyman Henn analyzed <br />the two proposed cross - section configurations with a near vertical highwall. Lyman Henn performed the analyses <br />using a computer program (Slope/W, GEO -SLOPE International) based on limit equilibrium theory to compute <br />Factor of Safety (FOS). A target FOS of 1.01 was used in the analyses to evaluate the temporary mining <br />condition. <br />Results of the laboratory data were evaluated to determine strength values for the subsurface materials. The target <br />FOS and chosen strength properties were determined with guidance from the Colorado Division of Reclamation <br />Mining and Safety (DRMS). Two borings conducted in 1999 by Haley and Aldrich (Reference 2), located <br />adjacent to the western boundary of Phase 7, were also reviewed for variability of subsurface materials and <br />anticipated depths. The selected values used in the analysis are summarized in the table below. <br />