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Mr. Allen Sorenson February 28, 2002 Page 2 of 4 depth to weathered shale in the areas of the necessary SSA. Along WCR 28, two soil borings identified an overburden depth of 12 feet and 15 feet with a depth to weathered shale of 56 feet and 43 feet, respectively, in the vicinity of the SSA. Along WCR 17, one soil boring identified an overburden depth of 7 feet with a depth to weathered shale of 50 feet in the vicinity of the SSA. Given this information, a SSA will be evaluated and setbacks recommended based on the resultant factor of safeties identified. The software used in the analysis is GSLOPE from MITRE Software Corporation. The slope of the mining face analyzed was taken as 2.0:1.0 (H:V) as indicated as part of the 112 Permit Application. The application also indicates that Owens Bros. Concrete proposes to excavate to a depth of 45 feet below the ground surface due to equipmenf (imitations. The reserves at the Nix site are to be excavated by wet mining methods; thus, the piezometric surtace, indicated by a dashed line in the analyses, simulate a saturated soil condition with groundwater approximately 3 feet below the ground surface. Given the above information as input criteria, two separate SSA's have been evaluated to establish setback limits for protection from damage to the utility poles. West SSA The results presented below give a minimum factor of safety for varying excavation offsets, measured from top of stops, a 45 foot excavation depth, and the slip surface drawn through the sand and gravel layer. As discussed above, the 45 foot depth is the proposed maximum excavation depth given the depth to weathered shale measures approximately 50 feet. The excavation slope face has been taken at 2.0:1.0 (H:V) and conservative soil properties used as identified is the fableaboue. WEST SSA -Minimum Factor of Safety with Varying Excavation Offsets 45 Foot Excavation - 50 Feet to Shale Excavation Offset (feet) 50 60 70 80 Factor of Safe 0.935 1.017 1.099 1.182 Note: Sfi surtace taken throw h sand and ravel la er. As a check, a similar analysis was performed to the one above, however, the slip surface was taken through the weathered shale layer as opposed to the sand and gravel layer. The results indicate that the weathered shale layer is more likely to fail than the sand and gravel layer, therefore, governing the scope stability analysis nn the wESt side. WEST SSA -Minimum Factor of Safety with Varying Excavation Offsets 45 Foof Excavation - 50 Feet to Shale Excavation Offset feet 70 80 90 100 Factor of D_752 0.811 0.868 0.937 Note: SG sur#ace taken throw h weathered shale la er. Based on pur discussions in the past, you indicated that if the offset distance, from the structure to top of slope, is twice the excavation depth, it can be assumed the structure will be protected