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3.3.4 Stability under Earthquake Loading <br />Previous analyses used an estimated peak ground acceleration (PGA) of 0.6g in seismic stability <br />calculations. Per the latest probabilistic ground motion data (shown in Figure 13), the annual <br />frequency of exceedence for 0.6g PGA acceleration is 6.17 x 10-5. This correlates to a <br />recurrence interval of 16,200 years which exceeds a typical design event for this type of dam. <br />This suggests the analyses presented are conservative. <br />le- <br />8 1e` <br />c <br />d <br />o�r <br />Xx <br />W 1 e'3 <br />0 <br />v <br />c <br />1e¢ <br />IL <br />m <br />e <br />e <br />a <br />1 e'` <br />lei <br />1e ie ` 1 e 1e' <br />Ground Motion (g) <br />(Reproduced from USGS, 2014) <br />Figure 13 Current Site Probabilistic Ground Motion <br />3.3.4.1 Pseudo Static Stability <br />Factors of safety for the pseudo- static analyses presented are acceptable (above typical minimum <br />design standards of 1.1). Failure Surface 4 on the downstream analyses was at the minimum <br />standard of 1.12. Some improvement in this factor of safety is expected due to strengthening of <br />the tailing due to consolidation and denaturation that has occurred since conditions that were <br />assumed in original design. Because the Design Report presented the more modern post - <br />earthquake liquefaction and deformation analyses, no further pseudo- static analyses is deemed <br />necessary. <br />San Luis Project Miller Geotechnical Consultants <br />Tailing Dam Data Report 20 February 2014 <br />