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' San Luis Mine Phase I[, Raise 2 ' S.0 CONCLUSIONS AND RECOMMENDATIONS The data collection and evaluations presented herein were conducted to confirm and finalize the ' conceptual designs for the embanlattent raise presented in the Amendment. Dynamic stability analyses based on a refined model of the structure confirmed that the conceptual raise design ' provides a stable structure and no modifications to this design were necessary. Deformation of the order of magnitude estimated for the raised embankment under the level of ' earthquake ground motion considered do not pose a threat to the integrity of the structure. The estimated deformations would not result in a loss of freeboard sufficient to allow escape of tailings solids or liquid, therefore positive containment would be maintained. Following the earthquake, the deformed crest of the embankment could be repaired if necessary to provide sufficient freeboard for full containment of PMF inflows or to eliminate any cracks which developed. t The primary concern with respect to deformations of the order estimated fot 0.6g PGA is the integrity of the liner system beneath the embankment. With 1-3 ft of displacement for a wedge type of failure involving sliding on the liner, there is a possibility that the geomembrane component of the liner system could be torn. However, as presented in the Amendment adequacy responses, ' several key factors reduce this possibility and the consequences should it occur. _ In addition, the analyses incorporated conservative shear strengths for the embankment fill and fill ' to liner interface, and true liquefaction of all saturated tailings at the start of the earthquake. The analyses also incorporated a conservatively high phreatic surface within the tailings whereas the ' actual level of saturation should be considerably lower and will reduce over time gas the tailings drain following closure. By employing conservative assumptions and approximations throughout the stability analyses the estimated displacements should be quite conservative. In the event the geomembrane liner is torn, the underlying soil component of the liner system would ' serve to limit the loss of contained fluids. Although the displacement analyses assume that failure occurs on a well defined plane, the actual failure surface through the embankment material would ' be a zone several ft or more in width which would distribute the strain in the liner over a similar zone. Since VLDPE liner can tolerate large strains, it is entirely possible that the liner would remain intact for displacements of the order of magnitude predicted. ' Assuming that the tailings are liquefied at the start of the earthquake and estimating deformations ' on this basis also represents a conservative method of analysis. For dams which are not highly sensitive to deformation during earthquake ground motions, such as a dam with a large free board or a tailings dam, a commonly adopted procedure when liquefaction is anticipated to occur is to ' evaluate the potential for the occurrence of a flow slide only. This type of analysis is frequently uy ~ 5_~ ro~ec[ o.