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<br />~• We do not believe the use of small benches (20 feet maximum width) will reduce <br />factors of safety below the required 1.3. <br />SUMMARY OF STABILITY CALCULATIONS <br /> <br />Portal Location Average Post- <br />Minin Slo a H:V Static Factor of <br />Safety <br /> Section A 2:1 1.7 <br />P3 Section B 2.5:1 2.1 <br /> Section C 2.8:1 2.0 <br /> Section D 2.4:1 2.0 <br /> <br /> Section E 2.3:1 3.3 <br />R1 <br />Section F <br />3.4:1 <br />3.0 <br /> Section G 2.4:1 2.1 <br />SUBSURFACE DRAINS <br />As discussed in the preceding section PROJECT DESCRIPTION, there is a <br />CJ <br />potential for some seepage out of the portal areas. For this reason we recommend <br />that a drain system be installed across the front of the portals at the approximate <br />locations shown on Figs. 3 and 5. There are several methods of installing a drain in <br />this area. In our opinion, the most practical method would be to compact a layer of <br />bacldilf up to the near the top of the portals. An interceptor drain trench can then be <br />excavated down through the bac~ll to the underlying bedrock soil. A conceptual <br />detail of the interceptor drain section is shown on Fig. 6. Our calculations indicate <br />that a gravel section of 12 square feet is capable of conveying flows in excess of 25 <br />gallon per minute. The drain should be sloped at a minimum 1 percent slope until the <br />drain daylights to existing grade. <br />LORENCITO COAL COMPANY, LLC <br />C7LR 25,663 <br />8 <br />