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BATTLE MOUNTAIN RESOURCES, SAN LUIS PROJECT CMLRO ADEQUACY LETTER RESPONSES Page 10 of 28 Irrespective of the iocation of the phreatic surface, an evacuation of tailings liquefaction can be made based on the grain size distributions and anticipated void ratios. Processing of the ore will produce tailings with 100 percent passing a No. 50 sieve (0.3mm). For the beach sands the void ratio is conservatively estimated to be 0.7 to 0.8 after consolidation (based on laboratory testing) and the grain size distribution should result in a D o size of approximately 0.25mm ar perhaps slightly smaller. Tai~ings sands which are located slightly further from the spigoting points than the "beach" sand is assumed to have a Ds size of approximately 0.15mm (No. 100 sieve) and avoid ratio of a.1 to 0.8. Even further from the spigots the tails can be assumed to be a fine sandy silt with a void ratio of 0.75 to 0.85. Work conducted by Seed and Idriss (1982), based on actual field performance of sites with a potential for liquefaction, was employed to evaluate the liquefaction potential of the tailings with characteristics as presented above (assuming 100 percent saturation). The results of this analysis are presented on Figure D.6-16 and as in the following discussion: No liquefaction of beach sands will occur for a void ratio of 0.8 if the seismic induced acceleration is less than 15 percent of gravity for a minimum of 15 cycles (site peak ground acceleration of .23g resulting from a Magnitude 7.5 earthquake approximately 28 miles away). No liquefaction of beaah sands at a void ratio of 0.7 can occur if the seismic induced acceleration is less than .25g for 15 cycles; No liquefaction of sands slightly further from spigot points will occur if seismic induced acceleration is less than .2g for 15 cycles; and No liquefaction of tails some distance from the beach if the seismic induced acceleration is less than .2g and no liquefaction at all if the void ratio is less than 0.8 under all but very extreme accelerations. From the analyses presented in the above discussions it does not appear that liquefaction of t t lingsaimnediately below the Phase 2 raises is likely to occur. ~LaFCOrtstir~'~i;or~oi~th-e)<k~af)Y~e'sl~f,~1 the- Phase 2' upstream~~raise3. It should be noted that in the event that the tailings materials are not suitable for construction of the upstream raises, sufficient space has been allowed downstream of the main "starter" embankment for construction of centerline or downstream raises.