2011-04-19_PERMIT FILE - M2011001

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Memo to Lafarge West, Inc. 2 April 19, 2011 Slope Stability Review File No. M-2011-001 Fences, Critical Location The applicant's cross section was duplicated for verification; no potential failure surfaces with lower safety factors than the applicant's identified critical slip circle were located. The safety factor produced by Galena is slightly higher than that produced by the applicant's formula. The accuracy of the applicant's analysis is confirmed (see attached). Communications Tower The applicant's cross section was duplicated for verification; no potential failure surfaces with lower safety factors than the applicant's identified critical slip circle were located. The safety factor produced by Galena is slightly higher than that produced by the applicant's formula. However, the cross section provided in the application and reviewed by the Division is flawed since the applicant did not account for the surcharge loads to pit slopes caused by topsoil stockpiles and the communication tower structure. Please review the proposed setback and cross section for accuracy related to surcharge loads imposed by stockpiles and structures and perform an updated slope stability analysis for the communication tower. Boyd Freedman Ditch The applicant's cross section was duplicated for verification; no potential failure surfaces with lower safety factors than the applicant's identified critical slip circle were located. The safety factor produced by Galena is slightly higher than that produced by the applicant's formula. The accuracy of the applicant's analysis is confirmed (see attached). Telephone Line The applicant's cross section was duplicated for verification; no potential failure surfaces with lower safety factors than the applicant's identified critical slip circle were located. The safety factor produced by Galena is slightly higher than that produced by the applicant's formula. The accuracy of the applicant's analysis is confirmed (see attached). Conclusion The Division will require the applicant to carefully review all setbacks and cross sections to check for accuracy related to surcharge loads and revise the proposed setback distances accordingly. If groundwater is intercepted shallower than expected and/or the soils differ from the expected profile, the applicant must contact the DRMS immediately and reevaluate the stability analysis based on the corrected information. The permit applicant must understand that any transgression of the offsets will be considered a serious violation of the permit if it is approved and issued. Enclosures