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Mr. Mark Campbell September 27, 2004 Page 5 claystone Bedrock ~~ CIVIL RES'~U RCES, LLC The proposed mine area is generally undedain by claystone bedrock. claystone is generally a weak bedrock and is often prone to slope instability and the bedrock foundation strength is critical for the highwall stability. For the claystone bedrock, two potential sUength conditions were considered. These strength conditions are referred to as:1j peak strength, and 2j residual strength. Peak strength is the maximum shear strength the claystone bedrock exhibits. The shear strength is made up of both cohesion (diagenetic bonding) and intemal friction. Under short-term conditions for unsheared claystone, peak strength governs behavior. If a sheared surface or sheared zone is present within claystone as a result of faulting, slippage between beds due to folding, past shrink-swell behavior, stress relief, or from a landslide, the cohesion along the sheared surface is reduced to zero, and the angle of intemal friction is decreased, due to alignment of clay minerals parallel to the shear plane. Under these conditions a claystone exhibits its lowest strength known as residual strength. Residual strength bedrock occurs in discrete zones, parallel with the sheared surface or zone, whereas fully softened strength occurs over a broader area. The engineering and index properties of the bedrock used for the stability analyses are shown in Table 1. Based on data from other recent jobs, and engineering judgment, we modeled the claystone as follows: Dry Unif Weight (pcf) Moisf Unit Weight (pcQ Saturated Unit Weight (pcQ Cohesion C psf Friction Angle ~'° f 16 119 123 Peak = 500 Peak = 26 Residual = 0 Residual =15 STABILITYANALYSES RESULTS Setbacks listed in Table 2 indicate the minimal setback from the structure to the mining limits. The setback distance can be increased as needed to address other restrictions. TABLE 2 -SLOPE STABILITY RESULTS AND SETBACKS Section Location Critical Structure Modeled Surchar e, sf Setback, ft Factor of Safe 1 Villano ~ Oil Well 500 110 1.02 2 Sasaki HWY 85 300 50 from Pro 1.03 3 Watada WCR 27 250 55 from Pro 1.01 4 Yokooji WCR 6 _ _ _ 250 35 from Pro 1.00 CONCLUSIONS Based on the stability analyses, the proposed mining extent limits on the eastern portion of the site was greatly influenced by WCR 27. As a result, we propose the following locations for the extent of mining offsets inside of the property boundary. Boundary Section Easement Location of Utiti Thickness of Mudlens Extent of Mittirtg from Pro a Line North Bounda 1 None .None None 25 feet East, WCR 27 2 60` ROW None None 55 feet Gas Well, North Central & Central 3 200' Utility See Figure 1 None 110 feet South, WCR 6 4 50 ROW None None 25 feet