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Mr. Ken Lambrecht <br />April 4, 2006 <br />Page 4 <br />Reclamation Hirhwall <br />We understand that if the gravel pit highwall is to be mined at a 3:1 the setback distance will be set at a <br />predetermined distance of 16 feet. Therefore in this second scenario we did not try to optimize this <br />distance. Instead we modeled the 16-foot setback distance and presented the factor of safety. As the <br />factor of safety is relatively high only the deepest bedrock section was modeled. <br />Table d below summarizes the results of our analysis. Typical required factors of safety for temporary <br />mine slopes and reservoir embankments are provided for comparison. Output graphics for each of the <br />analyses are attached. <br />Table 4: Hi hwall to Slur Wall Setback En 'neerin Anal sis Results <br /> Setback Catcutated Typical Required <br />Mode[ Distance (feet) F~Q or of Factor of Safety <br /> <br />Temporary Mine <br />O.S:1Highwall Shallow 10 1.33 1.2 <br />Section <br />Temporary Mine 0.5:1 <br />HighwallIntetmediate 30 1.26 1.2 <br />Section <br />Temporary Mine 0.5:1 <br />Highwall Deep Section 30 1.26 1.2 <br />with weathered bedrock <br />Long Term Compacted <br />Clay Slope Liner Full 20 1.81 1.5 <br />Reservoir <br />Long Term Compacted <br />Clay Slope Liner Rapid 20 1.21 1.2 <br />Drawdown <br />Long Tenn 3:1 Mined 16 21 <br />2 1 <br />5 <br />Slo e . . <br />Feathered bedrock is present, the mine highwall setback should be 30 feet from the slurry wa]] using <br />steep highwall alternative. Please see Figure 1 for a graphical representation of the steep highwall <br />mative setback distances. <br />highwall is mined at the final reclamation s]ope of 3:1, a 16-foot setback provides adequate <br />summary, a 16-foot setback from the slurry wall to a 3:1 mining slope provides an acceptable <br />lculated factor of safety. If a steeper highwall is desired, a 37-foot setback between the slurry wall <br />d the top of slope is required along the eastern side of the pit to meet DMG requirements. Along the <br />maining sides where no adjacent structures are within 200 feet, a setback distance from the slurry wall <br />the top of slope is 10 feet for the shallow section and 30 feet for the intermediate and deep sections. <br />