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iiiiiiiuiiuiuiii <br />999 <br />STATE OF COLORADO <br />DIVISION OF MINERALS AND GEOLOGY <br />Deparlmenl of Natural Resources <br />1713 Sherman SL, Room 215 <br />Dem-er, Colorado 80'03 <br />Phone 0031 8557557 <br />FAX: 13031 832 8105 <br />interoffice <br />MEMORANDUM <br />to: Jim Burnell <br />from: <br />subject: <br />date: <br />Reference: <br />gyrrff Ci. Walker <br />Yoast TR-06; Stability Analysis for Pond 011 <br />7 July 1997 <br />Memorandum, Routten to Walker, July 1, 1997, same subject. <br />~~~~~ <br />DEPARTMENT OF <br />NATURAL <br />RESOURCES <br />Roy Romer <br />Governor <br />~ame~ S Lochheazl <br />Exrcwive Direcor <br />M¢hael B Long <br />Division Director <br />The purpose of this interoffice memorandum is to provide you with my review comments on the <br />Geotechnical Investigation & Slope Stability Analysis, Proposed Yoast Mine Sediment;aiou <br />Pond 011, SE I/4 of Section l6, TSN, R87W, Routt County, Colorado, prepared for Seneca Coal <br />Company by North West Colorado Consultants, Inc. (the Report). <br />The geotechnical work is commendable, as is the report format and presentation. However, the <br />Slope Stability Analysis (analysis) appears to be deficient, as is the packet (Application Form For <br />A Revision To A Coal Mining And Reclamation Permit) I reviewed as regards pond design <br />(design). <br />The analysis presents a single circle (failure surface) with a factor of safety of 1.37 (an x <br />coordinate of 202.0, a y coordinate of 84.0, and a radius of 54.0). Using [he same geotechnical <br />information and dam configuration as presented in the analysis, there appears to be a potential <br />failure surface with a factor of safety of 1.18 (x = 220, y = 95, r = 66.9), below the Rule 1.3 <br />[4.05.6(11)(k)]. Recommend the analysis statement found on the last line of page 5 and first line <br />of page 6 be validated. <br />Although the pond is described in the Report, no plan and specifications (design) in regard to the <br />pond were found in the packet. <br />Please see me if you have any questions concerning this review. <br />cc: Routten <br />Hernandez <br />