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Geotechnical /Environmental Engineering • Materials Testing August 15; 2005 Twentvmile Coal Company 29515 Counri~ Road #27 Oak Creek. CO 80469 Attn: Mr. Jerry Nettleton Job Number: OS-6671 Subject: Slope Stability Evaluation -Intake Shaft Facility Sedimentation Pond - Twentymile Coal/Foidel Creek Mine; Routt County, Colorado. Dear Mr. Nettleton, This report presents the results for the Slope Stability Evaluation completed for the proposed SedimentatOn Pond to be constructed at the Intake Shaft Facility that is located at the Twentvmile Coal- Foidel Creek Mine in Routt County, Colorado. It should be noted that our firm previously completed a Geotechnical/Pavement Design InvestigatOn for the Intake Shaft Pad and Access Road to be conswcted at the subject site. The pret~ous report was prepazed under our job number 03-5838 and dated December 19, 2003. Proposed Construction: It is our understanding that the sedimen*atien pond t+~ll be corstructed at the northeast comer of the proposed 11.1 acre pad and the pond will be approximately 1 acre in size. We also understand that the pond will conswcted by excavating into the natural soils at the site and that no embankment fills will be required for the pond. The maximum pond depth will be 6 feet and the interior slopes of the pond will be constructed with 2 (Horizontal) to 1 (Vertical) side slopes. We also understand that the pond wril] be constructed with 1 foot of freeboazd. Subsurface Conditions: Two test holes were drilled at the proposed pad site and near the proposed sedimentation pond on November 21, 2003. The test holes (#5 and #6) were drilled as part of the previous Geotechnical Investigation completed for this site. The subsurface conditions encountered in the test holes were fairly uniform and generally consisted of a thin layer of topsoil and organics overlying natural clays and claystone bedrock materials, which exKended to the maximum depth investigated, 18 feet. The clays were slightly sandy, moderately to highly plastic, stiff to very stiff, slightly moist to moist and brawn in color. A sample of the natural clays classified as a CL soil in accordance with the Unified Soil Classification System. Claystone bedrock was encountered beneath the clays at a depth of approximately 7 feet beneath the existing ground surface and the bedrock materials exKended to the maximum depths investigated. The claystone bedrock materials were nil to sandy, fine grained, hard to very hazd, moderately to highy plastic, slightly moist to moist and brown to gray in color. Samples of the claystone bedrock classified as CL and CH soils in accordance with the Unified Soil Classification System. The test • (970) 879.7888 • Fax (970) 879.7891 2580 Copper Ridge Drive • P.O. Box 775226 • Steamboat Springs, CO 80477