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Mr. Robert Ray <br />June 5, 2009 <br />Page 3 <br />The scenarios modeled were: <br />¦ Poudre River Trail Section and Fence - 2.5 feet of overburden clay overlying 32.5 feet <br />of sand and gravel, over a 1 foot thick clay lens overlying an additional 4 feet of sand and <br />gravel. The trail and fence are approximately 80 feet away from the proposed mine limit. <br />• Gas Line Section - 3.0 feet of overburden clay, overlying 30.5 feet of sarld and gravel. <br />This gas line is 150 feet from the proposed mine limit. <br />Beneath the alluvium both sections were modeled with 2.5 feet of residual strength bedrock on top of <br />claystone bedrock. <br />Stability analyses were run on over 2,100 randomly generated circles generated at the mine <br />excavation and highwall, as well as at the nearby permanent structure. The Slope W program <br />calculated the Factors of Safety (FOS) using the ordinary, Bishop, Janbu, and Spencer Methods. <br />Graphic profiles of each analysis are included in Attachment A. The results of the analyses are listed <br />below: <br /> Distance to Nearest <br />Section <br />Permanent Structure Factors of Safeity <br />Poudre River Trail/Fence 80 1.4 <br />Gas Line 150 2.3 <br />The minimum setbacks are equal to the distances in the table above. All FOS are 1.4 or greater. <br />Mining, following these minimum setbacks, should not pose a hazard to nearby structures. <br />LIMITATIONS <br />Our review is based on regional geologic mapping, present mining plans, borehole data, known <br />structure locations, and stability analyses using typical soil strength parameters. Should the mining <br />plans change, subsurface conditions vary or structure locations differ from those portrayed in this <br />letter, we should be contacted in order to re-evaluate the potential affects on man-made structures. <br />Please call with any questions or comments. <br />Sincerely, <br />TETRA TECH <br />` eremy Deuto, P.G. <br />Engineering Geologist <br />4Garyy /inden,G. <br />Project Manager <br />GL:em <br />Attachments: Figures 1 - 4 <br />Attachment A <br />P:\23511\133-235 1 1-08005\Deliverables\DRMS\Application Package\Stabdity Exhibit\.Stability Analysis Letter 6-5-09.doc