2009-12-28_PERMIT FILE - C1996083

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• characterize the foundation conditions. The findings of the geotechnical investigation are summarized in this section. The boreholes were drilled with a Simco 2800 H.S. truck - mounted drill rig using 4 solid stem continuous flight augers. Soil samples were generally obtained at using standard split spoon and split -spoon "California" samplers. Standard penetration tests (SPT) were conducted in general accordance with ASTM D 1586 to characterize the density or consistency of the subsurface materials. The recovered soil was logged by a geotechnical engineer, and representative samples of subsurface materials encountered were brought back to our laboratory for detailed examination and testing. Borehole logs from the site investigation are presented in Appendix B. Laboratory test results are presented on the borehole logs and discussed in detail by BGI (2007). Each borehole was surveyed. Borehole locations are summarized in Table 1 and are presented on Drawing No. 2 in Appendix A. Table 1. Summary of Borehole Locations Borehole ID Northing Easting Elevation ft BG06 -08 BG06 -09 19199.473 19244.225 36576.666 36741.274 6107.9 6107.0 • As previously indicated, boreholes BG06 -08 and BG06 -09 were drilled on a bench excavated into the native soils for the Refuse Pile No. 4 footprint. The contractor indicated that the surface elevation of the boreholes was approximately 10 vertical feet above the final proposed subgrade for the refuse pile foundation. As indicated on Drawing 2 in Appendix A, the boreholes were located near the toe of the proposed CWDA No. 4. Borehole BG06 -08 was located on the western end of the bench, while borehole BG06 -09 was located on the eastern end of the bench. Native soils on this slope consist of colluvium and slope wash materials originating from sedimentary units on the slope above. Soils encountered during drilling generally consisted of dry to damp, hard, moderate brown clayey gravel, cobbles, and boulders. By nature, colluvial /slope wash soils such as these are heterogeneous. Accordingly, the fines content and the rock content varied somewhat both laterally and vertically. The boreholes were advanced to total depths of 37 and 57 feet. Each borehole was terminated due to significant deflection of the augers by large boulders at depth. No bedrock or groundwater was encountered in either borehole. SPT "N- values" ranged from 34 blows per foot to 50 blows for zero inches, indicating hard soil consistency and cobble /boulder content. Recovered samples were also noted to be hard, consistent with the blow counts. 0 Bowie No 2 Refuse Pile No 4 2009 Revised stability.doc Project #06- 481 -003 Page 5 of 12