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Mr. Jim McFarland November t9, 2002 Page 4 STABILITYANALYSES Inc We performed stability analyses in order to evaluate potential for damage to existing permanent structures due to mine highwall slope failures at each mine pod. Analyses were performed with the XSTABL computer program. For each mine pod we analyzed the most critical soil profile(s) based on exploratory boring data. The slope of the perimeter mine excavation was drawn at 0.5:1 (horizontal to vertical). Slurry walls were modeled 50 feet from the top of the perimeter mine slope. In addition, a 20- foot construction buffer was incorporated between the slurry wall and nearby structures or cliffs to allow sufficient space for slurry wall constmction. Groundwater levels on the profiles were inputted to pomay site dewatering when nearby ditches carry water. No laboratory strength tests were performed on soils at the site. The soil strength parameters used were based on typical values for the anticipated soils and our experience at other sites in the area. The inputted strength parameters were: Material Moist Unit Saturated Unit Elective Cohesion Effective Friction Wei ht (c Wei ht (c (c An (e (de reesJ Overburden clay and cla lenses 114 126 50 28 Sl walls 110 122 0 0 Sand and avel 130 137 0 35 Bedrock 124 134 100 28 The scenarios modeled were: Pod 1 -Five feet of overburden clay, overlying seven feet of sand and gravel, over 11 feet of clay lens, over 10 feet of sand and gravel, on top of claystone bedrock. In addition, a surcharge load of 1,200 psf was placed 10 feet from the top of the mine highwall to model overburden stockpiles approximately 10 feet high and 20 feet wide. • Pod 2 -Ten feet of overburden clay, overlying 32 feet of sand and gravel, on top of claystone bedrock. For the mine perimeter, a slurry wall was modeled 50 feet from the top of the mine highwall and 20 feet from nearby structures. A second analysis was performed on the same profile without a slurry wall to investigate stability where gas lines cross under the Merit well access roads. • Pod 3 -Seven and one-half feet of overburden clay, overlying six and one-half feet of sand and gravel, over seven feet of clay lens, overlying 12 feet of sand and gravel, on top of claystone bedrock. Pod 4 -Four feet of overburden clay, overlying 31 feet of sand and gravel on top of claystone bedrock. A slurry wall was modeled 50 feet from the mine highwall and 20 feet from nearby structures.