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• Subsurface Conditions <br />The subsurface conditions described below are based primarily upon the <br />borings performed for the current investigation. The locations of the borings are <br />shown on Sheet 1. Logs of the borings are presented in Appendix A. Schematic <br />logs are also shown on the RDA cross-section shown on Sheet 3. <br />The soil types encountered in the borings consisted of about 4 feet of clay <br />cover fill in borings TH-201, TH-202 and TH-203 located on the finished benches of <br />the RDA. Coal refuse was found from the surface or below the clay fill to depths 35 <br />to 97 feet. The depth of the coal refuse correlated reasonably well with the pre-RDA <br />topographic information. The coal refuse deposit was relatively consistent, no <br />significant clay layers or anomalous deposits were noted. The engineering <br />properties of the coal refuse are discussed in detail in following sections. <br />• Avery dense clayey sand or possible weathered bedrock layer was logged <br />below the coal refuse . This layer was comparatively thin, typically 3 to 5 feet thick. <br />The layer was primarily identified by drilling resistance and vibration, essentially the <br />drilling "smoothed out" over this interval just prior to encountering very hard <br />bedrock. We interpret this layer as a combination of a disturbed soil zone created <br />during stripping and weathered bedrock before encountering sandstone. The <br />bedrock in the area of the RDA is mapped as arkosic sandstone, siltstone and shale <br />of the Raton Formation (Reference 16). The bedrock found in the borings consisted <br />of hard to very hard, interbedded sandstone and sandy shale. <br /> <br />9 <br />