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• SCOPE This report presents the results of our Geotechnical Investigation for the proposed South Taylor Sedimentation Pond Embankments. Our investigation includes review of ourprevious investigations at the site, geologic reconnaissance, subsurtace investigation, "laboratory testing, stability analysis and constructionlmonitoringrecommendations. The field investigation and laboratory testing was performed in 1999, with a draft report issued under CTL~T Job No. 28,585. The current report utilized the previous information and was prepared In accordance with our Proposal No. 02-0799. SUMMARY OF CONCLUSIONS We advocate a conservative approach to embankment design. We recommend an upstream slope of 3:1 (H:V) and a downstream slope of 2:1. We also recommend a keyway trench at the hase of the embankment with a minimum width of 8 feet and a minimum depth of 6 feet (Fig. 3). The keyway should be continuous below the dam, extending into and up the abutments. The upstream face and spillway should be protected from erosion as required. Our stability analysis indicated Factors of Safety of over 2.0 for both the upstream and downstream slopes forend of construction, rapid drawdown, or steady state conditions. This is significantly over the regulatory minimums. PROJECT DESCRIPTION The South Taylor surtace mine will be located north of the West fork of Good Spring Creek. Two sedimentation ponds are planned below the fill (Fig. 1). The pond embankments will be constructed primarilyfrom soils excavated in and around the pond. The intent Is to construct the embankments as far south as possible to maximize volume, while still abutting the valley connecting side to minimize KENNECOTT ENEROV COLOWYO COAL COMPANY • SOUTH TAYLOR 6EDIMENTATION POND OTL~T JOB NQ J5,86~ 1 • Exh. 7-20F-5 Revision Date: 1/05/07 Revision No.: PR-02