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TETRA TECH <br />Ms. Kristen Fienberg <br />July 26, 2011 <br />Page 2 of 2 <br />If the slope fails, the integrity of the tower foundation may be compromised. It is <br />TowerCo's position to enforce at (east a 2.0 safety factor, and we reserve the right to <br />increase that safety factor as we deem necessary. <br />The 2.0 safety factor you are referring to relates to the bearing capacity of the soils <br />underlying the tower not the slope stability of adjacent mining. Using the DRMS's <br />conservative standards and recommended surcharging, the proposed mining slopes have <br />been deemed stable by our geotechnical engineers as well as by the DRMS. Attached is a <br />copy of the DRMS approved stability exhibit for the mine area near the TowerCo tower. The <br />slope stability factor of safety (not the capacity of the soils underlying the tower factor of <br />safety) is 1.3 which is greater than the minimum 1.0 factor of safety required by the DRMS. <br />Once again, Tetra Tech and Lafarge would strongly encourage you or your engineer to call and talk <br />to one of Tetra Tech's geotechnical engineers about any additional concerns you may have. We <br />believe that discussing the Stability Analysis Report with you will be the best way for us to make sure <br />you understand how the report was prepared and the report's findings. If you are interested in <br />accepting our offer, please contact me so that I can facilitate the scheduling of a conference call. I <br />can be reached at pam.hora(c�tetratech.com or 720 - 864 -4507. <br />Sincerely, <br />TETRA TECH <br />• Pame a Franck Hora, AICP <br />Senior Planner <br />Attachments <br />cc: Anne Best Johnson, AICP, Lafarge West, Inc. <br />P:\23511\ 133 - 23511- 10002 \ProjMgmt \Correspondence \TowerCo \Response to TowerCo 7 26 11 rev.docx <br />