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Y <br />TETRA TECH RMC <br />Mr. Jeff Gregg <br />January 28, 2003 <br />Page 3 <br />- Rural Ditch Lateral along the edge of Weld County Road 24'/<, approximately 70 feet to the <br />north <br />- Rural (irrigation) Ditch approximately 40 feet to the south <br />- Rural (imgation) Ditch approximately 65 feet to the southeast <br />- Proposed relocation of Rural Ditch Lateral approximately 65 feet to the east <br />- Kerr-McGee well and tank battery approximately 150 feet to the northeast <br />- Farm access road approximately 65 feet to the east <br />Pod 3: Phase 8 <br />- Godding Hollow (irrigation) Ditch approximately 70 feet to the west <br />- Cole (irrigation) Ditch approximately 65 feet to the east <br />- Co]e (imgation) Ditch approximately 70 feet to the south <br />- Rural (irrigation) Ditch approximately 65 feet to the north <br />Pod 4: Phase 9 <br />- Cole (irrigation) Ditch approximately 65 feet to the west <br />- Relocated Rural (imgation) Ditch approximately 65 feet to the north <br />- Relocated Rural (irrigation) Ditch approximately 65 feet to the northeast <br />- Last Chance (irrigation) Ditch approximately 140 feet to the northeast <br />- Relocated McCormick (imgation) Ditch approximately 70 feet to the south <br />STABILITYANALYSES <br />We performed multiple stability analyses in order to evaluate potential for damage to existing <br />permanent structures due to mine highwall slope failures at each mine pod. Analyses were <br />performed with the XSTABL computer program. For each mine pod we analyzed the most critical <br />soil profile(s) based on exploratory boring data and the mining plan. The slope of the perimeter mine <br />excavation was drawn at 0.5:1 (horizontal to vertical). On the southern part of the site where deeper <br />bedrock is present, slurry walls were modeled 50 feet from the top of the perimeter mine slope. On <br />the northern part of the site, slurry walls were modeled 40 feet from the top of the mine slope. In <br />addition, a 25-foot construction buffer was incorporated between the slurry wall and nearby <br />structures to allow sufficient space for slurry wall construction. Groundwater levels on the profiles <br />were inputted to portray site dewatering when nearby ditches carry water. <br />No laboratory strength tests were performed on soils at the site. The soil strength parameters used <br />were based on typical values for the anticipated soils and our experience at other sites in the azea. <br />The inputted strength parameters were: <br />