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Interoffice Memorandum <br /> <br />To: Rob Zuber <br />cc: Dan Hernandez <br />From: Zach Trujillo <br />Subject: Colowyo – TR-98 Second Review of Geotechnical Analysis <br />Date: 1/25/2013 <br /> <br />Rob – <br />After my review of Colowyo’s responses to the preliminary adequacy questions, I have the following comments: <br />1) DRMS: Two scenarios within the geotechnical analysis by Shannon & Wilson did not meet the minimum required <br />factor of safety (FS) of 1.5 as per Rule 2.05.3(6). These correspond to Case 2a and Case 2c. Please explain how long-term <br />stability is achieved in relation to the Division’s minimum requirements for slope stability of a temporary excess spoil <br />pile. This explanation may include an additional slope stability analysis regarding the temporary excess spoil fill showing <br />that with revised input parameters (more conservative than the average values but less conservative than the “low <br />bound” values used previously) the proposed excess spoil pile will meet the Division’s minimum requirements of 1.5 FS. <br />Colowyo: Colowyo has reviewed the Colorado Mine Land Regulations and does not agree that Rule 2.05.3(6) addresses <br />factor of safety (FS) in its entirety. Colowyo does not believe that any regulation within the Colorado Mine Land <br />Regulations speaks to a FS of 1.5 for a temporary spoil pile. Rule 4.09.1(7) does address a FS of 1.5 for excess spoils. <br />However, this rule does not specifically nor directly address temporary spoil piles. The rule does state that, “…covered <br />with topsoil or substitute material in accordance with 4.06…” which indicated a surface that is prepared for reclamation <br />and will be a permanent surface. Thus, this statement in the rules demonstrates that Rule 4.09.1(7) is directed towards a <br />permanent excess spoil and not a temporary spoil that is proposed under this technical revision. <br />The Division has also previously approved text in Colowyo’s PAP which addresses Rule 4.09.1(7). In Exhibit 21, Item 1, <br />Addendum No. 3-5, Shannon & Wilson’s report addresses a FS for a permanent fill in the conclusions section and it states, <br />“The Colorado Mined Land Reclamation Board regulations (2005) require a long term FS of 1.5 or greater for permanent <br />spoil fill slopes; they do not specifically address temporary slopes.” This statement by a professional engineer and <br />approved by the Division previously sets precedence that the Division agrees that the rules do not address a FS for a <br />temporary spoil pile. <br />In conclusion, Colowyo firmly believes it is meeting all the requirements of the Colorado Mine Land Reclamation Board <br />regulations with the FS that is presented in Addendum 4 of Shannon & Wilson’s report. Additionally, because the rules do <br />not specifically address a FS for a temporary spoil pile, Colowyo feels that a certified professional engineering report <br />presents the best alternative to calculating a FS utilizing current professional judgment and previously approved <br />materials, because the rules do not specifically address a FS for a temporary spoil pile. <br />DRMS: Rule 2.05.3(6) states that “Temporary overburden disposal (storage) structures shall comply with the applicable <br />performance standards of Rule 4…” Shannon & Wilson’s Addendum No. 4 analyzes the excess spoil pile in its entirety <br />which includes both the proposed temporary excess spoil and the previously approved permanent excess spoil pile. In <br />Shannon & and Wilson’s slope stability analysis of the entire excess spoil pile, their report shows potential failure paths <br />