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Mr. Edward Lanyon <br />November 12, 2014 <br />Page 2 <br />cross section of the area of concern. The cross - section was used to develop a slope stability <br />model using the computer software program Geo- Studio Slope1W. SEO regulations state that no <br />excavation shall occur within 200 feet of a jurisdictional dam. The proposed alignment for the <br />mine highwall around the Hatchery Pit is therefore at 200 feet from east from the toe of the <br />existing North Dahlia Dam. The mine highwall was modelled as a 0.5:1 (horizontal to vertical) <br />excavation slope 25 feet inside of the proposed slurry wall. Figure 2 shows a slope stability <br />model run using the proposed geometry and assumed soil parameters based on D &A's <br />experience with projects in the region. As the model shows, the factor of safety against a <br />downstream slope failure of the dam with a full reservoir and the assumed geometry is 4.6. The <br />SEO requires a factor of safety of 1.5 for a dam under this loading condition. <br />CONCLUSION <br />Based on the information supplied by Albert Frei and Sons and the City of Thornton it is the <br />option of Deere and Ault that the proposed Hatchery Pit should not propose any significant threat <br />during construction of a slurry wall or subsequent mining to the North Dahlia Dam and <br />Reservoir. <br />If you have any questions or comments please call. <br />Sincerely, <br />DEERE & AULT CONSULTANTS, INC. <br />Colby J Hayden, P.E. <br />Principal <br />DHF:sp <br />Attachments <br />cc: Ben Frei <br />QA0217 Albert Frei & Sorm10247.015 Hatchery PiASbpe StabilityWatchery Pit 0bje-tioo.Llr.Dmx <br />