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<br />Memo to Gregg Squire 3 Februazy 5, 2003 <br />construction report. The option to post a 20 percent bond at this time is not available to <br />Hall-Irwin at the Shore Resource site because mining has already intersected ground water. <br />The Operator is strongly encouraged to confer with the DMG prior to implementing any changes to <br />the slurry wall plans or specifications that may occur prior to or during construction. If substantive <br />changes to the plans and specifications aze implemented without DMG concurrence, and during <br />review of the final construction report DMG determines that the changes diminish DMG's degree of <br />confidence that the scurry wall will create an effective leakage barrier, the DMG may determine that <br />the Operator is not eligible for the 20 percent bonding option. <br />DMG has completed a review of the Tetra Tech RMC slope stability analysis for the Shores <br />Resource site dated January 28, 2003. The purpose of the stability analysis was to demonstrate that <br />the excavation setbacks proposed in the mine plan are sufficient to prevent damage to structures that <br />are not owned by the Operator. While the DMG has determined that the proposed mining setbacks <br />aze adequate, we do not agree with the mechanisms and assumptions employed in the stability <br />analyses the Applicant has provided. The DMG has identified the following issues with the <br />Applicant's stability analyses: <br />1. The analyses model the mined highwall at a slope of O.SH:1V. In practice, it is virtually <br />impossible to control the slope of a gravel pit highwall, and pits that are mined from the toe <br />of the slope aze typically neaz vertical to vertical. The DMG requires that for the purpose of <br />analysis, gravel pit walls be modeled as vertical unless that Operator can demonstrate that <br />the slope angle of the highwall will be controlled during mining. <br />2. The draft specifications for slurry wall installation state that weathered bedrock of uncertain <br />quality overlies bedrock. The DMG requires that the residual strength of the weathered rock <br />layer be considered in the stability analyses. <br />3. The Applicant analyzed only circulaz failures surfaces. In cases where the critical cross <br />section includes tabular strata, such as the slurry wall or the weathered bedrock, non-circulaz <br />failure surfaces must be considered. <br />The DMG has re-analyzed the Applicant's Phase 4 cross section in consideration of the forgoing list <br />of reservations, and determined that given the conservative nature of the analysis, e.g. vertical pit <br />wall and residua] strength weathered bedrock, the safety factors are adequate to protect the Godding <br />Hollow Ditch and the slurry wall. A copy of the DMG analysis is enclosed. <br />enclosure(s) <br />cc: Cazl Mount, DMG (w/enclosures) <br />Q\acsUly Documents\Shores.doc <br />