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i ~ Mr. Norm Roche June 30, 2000 Page 2 STABILITY ANALYSIS Inc We performed a stability analysis for the proposed maximum mine slope section using the XSTABL slope stability analysis program. The analysis was performed using the Bishop Method on randomly generated slip circles. The section analyzed was based on the boring data provided by Aggregate Industries and the mine plan. The section assumes a mine depth of 60 feet, a mine slope of 2:1 (horizontal to vertical), a slurry wall located 20 feet Behind the top of the mine slope, dewatered conditions on the mine side of the slurry wall, and saturated conditions on the backside of the slurry wall. The soil profile in the cross-section consisted of five feet of overburden clay overlying 37 feet of upper sand and gravel over a two-foot thick "mud lens," overlying 16 feet of lower sand and gravel, on top 5 feet of fully softened (weathered) claystone bedrock over peak strength claystone. No laboratory analyses were performed on soils at the site. The soil strength parameters that were input were based on typical values based on our experience, and are listed in the following table: Total Unit Saturated Unit Effective Effective Material Cohesion Friction Angle Weight (pcf) Weight (pcf) (pcf) (degrees) Overburden Clay 114 126 200 28 Upper and Lower Sand 130 137 0 35 and Gravel Mud Lens 114 126 200 28 Fully Softened claystone 124 134 50 20 Peak Strength claystone 124 134 500 28 Slurry Wall 100 105 50 14 The factor of safety was 1.55, indicating the mine slopes should be stable. A copy of the stability analysis cross-section is attached to this letter. STRUCTURES WITHIN 200 FEET OF DISTURBED AREAS The proposed mine site is in an agricultural area with relatively few above-ground structures. Structures within 200 feet of the proposed mine include State Highway 60; a short length of Union Pacific Railroad tracks; a barn and farm buildings; an irrigation ditch; and several gas wells and their associated separators, tank batteries, and pipelines. All known man-made structures and their approximate distances from the proposed mine areas are listed below: State Highway 60 located approximately 70 feet west of the proposed mine at its closest point;