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Project 06605 <br />Page 2 of 2 <br />The soils anticipated to existing at this site will have varying angles of repose. <br />The soils that will control the stability of the slope are anticipated to be the sand <br />and gravel layer. Based on our experience in this area and reference geotechnical <br />engineering literature ("Fundamentals of Geotechnical Analysis" by I. S. Dunn, L. <br />R. Anderson and F. W. Kiefer) an anticipated conservative angle of internal <br />friction for this material is approximately 26°. This is based on the assumption <br />that dewatering will keep the face of the pit moderately dry during the period of <br />time that the pit is active. This corresponds to a slope of just over 2:1. It has been <br />our experience that the risk of instability at that slope is low. Additionally, based <br />on experience at the nearby pits (Idaho Creek Pit and Cottonwood Pit) we aze <br />recommending a maximum slope of the pit walls of 2:1 (2 horizontal to 1 <br />vertical). <br />Therefore at a maximum assumed depth of mining of 20 feet, a minimum setback <br />of 40 feet from any man made structure will afford adequate protection from the <br />risk of slope instability. <br />Thank you for consulting with us on this phase of the project. If you have any <br />questions concerning this report, please do not hesitate to contact us. <br />Sincerely, <br />~,.:~:: <br />i~see~b o~=~ <br />niltli.vt ~ , <br />:rr z ; ., ~,,, <br />SCOTT, COX AND ASSOCIATES, INC. <br />By <br />M. Edwar G ssgow, PE <br />Professional Geologist <br />