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5.0 GEOTECHNICAL STUDIES <br />Subsurface and geotechnical field investigations were conducted between <br />1976 and 1985 at Mountain Coal Company's WEM facility by International <br />Engineering Company, Inc. (1976), Chen and Associates (1980), Geo-Hydro <br />Consulting, Inc. (1980), Michael Baker, Jr., Inc. (1985), and Envirocon, Inc. <br />(1993 & 1994). Data from these investigations have been used to perform this <br />slope stability analysis. <br />5.1 Tono2rauhv and Geoloey <br />The URP area is a natural bench with an average 5% slope to the north. <br />The bench extends approximately 2600 feet east-west, and 1600 feet north- <br />south. Two competent north-south oriented bedrock ridges flank eastern and <br />western limits of the bench. Beyond eastern ridge the terrain drops into <br />Sylvester Gulch; beyond the western ridge the terrain drops steeply into an <br />unnamed ravine. South of the bench the ground rises steeply 600 feet to a <br />broad plateau. The face of this rise appeazs quite stable,. being thickly covered <br />with old growth pine, scrub oak, and aspen vegetation. The northern limit of <br />the URP area is rimmed by a sloping face which extends down 240 feet in <br />elevation to the WENI main portals; about 170 feet farther below is the large <br />bench where the existing WENI surface facility is located. <br />The bench structure consists of 30 to 60 feet of colluvial slope wash <br />overburden material, beneath which lies massive sandstone layers of the <br />cretaceous Mesaverde formation. Figure 5 shows cross-section A-A' from <br />Figure 1. This cross-section has been constructed from drill logs from wells <br />SObI-7, SONI-8, SONI-127H, and SONI-13 (see Appendix A), and surficial <br />locations of rock outcrops and freshwater springs. Continuous bedding planes <br />throughout the cross-section suggests highly competent structural geology. All <br />6 <br />