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TETRA TECH RMC <br />Mr. Jeff Gregg <br />January 28, 2003 <br />Page 4 <br />Material Moist Unit <br />Wei ht (c Saturated Unir <br />Wei ht (c EffeMive Cohesion <br />(c Effective Friction <br />An le (de rees) <br />Overburden cla 114 126 50 28 <br />Sl walls I10 122 0 0 <br />Sand and avel 130 137 0 35 <br />Bedrock 124 134 100 28 <br />The scenarios modeled were: <br />Phase 4 -The most critical section in Phase 4 was based on boring data in the southeast part <br />of Phase 4 near the Godding Hollow Ditch. The profile consisted of six feet of overburden <br />clay overlying 32 feet of sand and gravel on top of claystone. A slurry wall was modeled 50 <br />feet from the mine highwall and the Godding Hollow Ditch was modeled 25 feet from the <br />slurry wall. The analysis was run both with and without an overburden stockpile surcharge <br />placed 10 feet from the highwall for a width of 20 feet and surcharge pressure of 1,200 psf. <br />The resulting factors of safety at the Godding Hollow Ditch were 2.2 with the surcharge and <br />1.9 without the surcharge. <br />Phase S -Phase 5 will have a perimeter slurry wall on its east and west sides. The setbacks <br />will be the same as in the case of Phase 4 (above). However, the mine highwall will be <br />thinner in Phase 5, thus the highwall will be more stable than that modeled in Phase 4. The <br />north boundary of Phase 5 is near the Rural Ditch and will not include a slurry wall. Based <br />on the boring data, we modeled a slope profile consisting of six feet of overburden clay over <br />18 feet of sand and gravel on top of claystone. The Rural Ditch was offset 40 feet from the <br />highwall, and the analysis was run both with and without a 20-foot wide, 1,200 psf surcharge <br />located 10 feet from the highwall. Resulting factors of safety at the Rural Ditch were 1.9 <br />with the surcharge and 1.6 without the surcharge. <br />Phases 6 and 7 -Phases 6 and 7 are essentially one large mine pod located on the north part <br />ofthe site in an area ofrelatively shallow bedrock. The north, west, and east sides of Phases <br />6 and 7 aze enclosed by a slurry wall. The south boundary is the Rural Ditch with no slurry <br />wall. We modeled a slurry wall profile along the southeast part of Phase 7 near the Rural <br />Ditch. The profile was six feet of overburden clay overlying 18 feet of sand and gravel on <br />top of claystone. The shiny wall was setback 40 feet from the highwall and the ditch was 25 <br />feet from the slurry wall. The analysis was run both with and without the 1,200 psf <br />surcharge. The factor of safety at the ditch was 2.5 without the surcharge and 3.8 with the <br />surcharge. For the south part of Phases 6 and 7 (near the Rural Ditch), we modeled <br />essentially the same profile as we modeled on the other side of the ditch for Phase 5 (40-foot <br />setback foundation), only the topography was changed to reflect the mined out Phase 5. The <br />