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Interoffice Memorandum <br />To: Jim Stark <br />From: Zach Trujillo <br />Subject: Colowyo —TR -105 Review of Geotechnical Analysis <br />Date: 8/5/2018 <br />Jim — <br />I after my review of Colowyo's Addendum No. 5 to Geotechnical Study for Excess Spoil TR -105, I have no adequacy <br />questions regarding the changes to the South Taylor Fill changes. <br />West Area <br />The West Area fill has been modified to reduce the slope at a section of the fill while maintaining a similar elevation. As <br />a result, the new incline will begin lower in elevation than originally approved to compensate for the reduced overall <br />slope. Geotechnical analysis and slope stability calculations as part of the approved "Revised Addendum No. 3 to <br />Geotechnical Study of Excess Spoil Fill Stability", the safety factor for this fill were calculated at 1.5. With the reduced <br />slope along the fill, it is expected that the change from 2.5H:1V to 3.4H:1V will increase the safety factor as stated in <br />Addendum No. 5. Shannon & Wilson, Inc.'s (SW) analysis is accurate and sufficient for the West Area fill. <br />East Area <br />As part of the East Area fill's geotech analysis in Addendum No. 3, it was concluded that infinite slope stability analysis <br />would be the most critical case. Based upon this, the general calculation for safety factor for infinite slope analysis can <br />be broken down to the tangent of the friction angle divided by the tangent of the slope of the fill. This calculation was <br />used in SW analysis for the change in the East Area fill. The safety factor is calculated at 2.6, well above the minimum 1.5 <br />required. All necessary demonstrations and calculations were included with Addendum No. 5. <br />If you have any questions, feel free to contact me. <br />Sincerely, <br />Zach Trujillo <br />