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5 Z <br />SMITH WILLIAMS CONSULTANTS, INC. <br />• <br />^ For collapsed excavations where the depth to bedrock is greater than 7 feet below the <br />final SLF subgrade surface: Excavate collapsed materials from shafts to a depth of <br />25 feet below the SLF subgrade surface, then backfill with coarse shaft backfill to <br />approximately 3 feet below the soil/bedrock interface, and then place concrete, <br />cemented rock fill, and structural fill. <br />^ Excavate shallow surface pits to rock or to 25 feet below the SLF subgrade surface <br />(whichever is less), then backfill with compacted select structural fill and/or structural <br />fill to the final SLF subgrade elevation. <br />^ For shallow mine adits and tunnels: Collapse the crown pillar by drilling and blasting, <br />excavate collapsed crown pillar, backfill with coarse shaft backfill, then install a <br />geogrid cap. <br />The areas requiring remediation have been initially identified from the available information. <br />Remediation activities will involve further investigations to provide more detail on the type and <br />extent of mine workings that may need to be remediated. Each feature observed on surface, and <br />identified underground as potentially requiring remediation, will be re-assessed thoroughly again <br />• as part of the remediation process; and the final remediation requirements will be based on these <br />re-assessments. <br />2.5_Seismicity <br />Based on the- seismic- evaluation submitted as part of Amendment No. 8, a PGA of 0.14g was <br />selected for the VLF during operations, and a PGA of 0.08g was selected for the VLF at closure. <br />No change to these. values was warranted for the Phase 5 VLF design. <br />C7 <br />S:\PROJECTS\1125 CCBV PHASE 5 VLF\H2 - DESIGMAREQUA VLF\VLF PHASE 5 FINAL REPORT V2.DOC 16 <br />