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Banks and Gesso <br />April 3, 2007 <br />Page 2 <br />SUBSURFACE CONDITIONS <br />A generalized subsurface profile was developed by Lyman Henn and was based upon our review of several <br />documents: <br />- Reclamation Permit Application (Reference 1); <br />- water well log information provided by Banks and Gesso; <br />- Lafarge drawing dated 7/18/03 with drilling information from the reserves analysis, provided by <br />Banks & Gesso; and <br />- NRCS Soil Survey for EI Paso County, Colorado (Reference 2). <br />The subsurface conditions aze assumed to consist of approximately 6 to 10 feet of overburden consisting of sandy <br />clay to clay, 25 to 30 ft of sand and gravel, and 4 ft of highly weathered claystone/shale bedrock underlain by <br />claystone/shale bedrock. For the purpose of analyses, the depth to bedrock is assumed to be 40 ft. The natural <br />static groundwater is assumed to be approximately 1 ft below existing grade, and during mining Lyman Henn <br />assumes that the piezometric surface will be drawn down by dewatering to the top of the weathered bedrock. <br />ANALYSES <br />Lyman Henn performed an analysis of two proposed excavation configurations: 1) mining to a temporary near- <br />vertical highwall, and 2) mining to a stable temporary slope with a 25 ft setback between the top of excavation <br />slope and adjacent existing structures. Lyman Henn performed the analyses using a computer program (Slope/W, <br />GEO-SLOPE International) based on limit equilibrium theory to compute Factor of Safety (FOS). A target FOS <br />of 1.01 was used in the analyses to evacuate the temporary mining condition. In the absence of laboratory data, <br />reasonably conservative values for the subsurface materials were used in the analysis, as tabulated below. The <br />presence of the weathered shale, the target FOS and [he strength properties were all chosen with guidance from <br />the Colorado Division of Reclamation Mining and Safety (DRMS) and are typical of DRMS's expectations for <br />sites where specific geotechnical data is not available. <br />Depth Effective Moist Unit Saturated Unit <br />(ft below Material Friction Angle Effective Weight Weight <br />existing grade) ~' (degrees) cohesion c (psf) Ym (pct7 Y~ p ~ <br />(c <br />10 Overburden 28 50 114 _ <br />10-40 Sand and Gravel 35 0 -- 137 <br />40-44 Weathered Shale 14 0 -- 135 <br /> Shaley -- <br />44+ claystone/ 28 100 135 <br /> Sandstone <br />