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Cripple Creek&Victor Gold Mine <br /> Valley Leach Facility 2 Phase 3 ■ <br /> Detailed Design for Permitting,Revision 1 <br /> NewFields Project No.475.0106.033 <br /> July 2020 <br /> to approximately 10 feet below the SLF subgrade surface and then place a <br /> concrete plug, cemented rock fill, and structural fill to achieve SLF subgrade <br /> surface. <br /> o For collapsed excavations where the depth to bedrock is greater than 7 feet below <br /> the final SLF subgrade surface: Excavate collapsed materials from shafts to a depth <br /> of 25 feet below the SLF subgrade surface,then backfill with coarse shaft backfill <br /> to approximately 3 feet below the soil/bedrock interface, and then place a <br /> concrete plug, cemented rock fill, and structural fill to achieve SLF subgrade <br /> surface. <br /> > Excavate shallow surface pits to rock or to 25 feet below the SLF subgrade surface(whichever <br /> is less), then backfill with compacted select structural fill and/or structural fill to the final <br /> SLF subgrade elevation. <br /> For shallow mine audits and tunnels: Collapse the crown pillar by drilling and blasting, <br /> excavate collapsed crown pillar, backfill with coarse shaft backfill,then install a geogrid cap. <br /> 2.4. Seismicity <br /> A seismic hazard assessment was previously included by as part of the VLF Design Report(AM EC, <br /> 2011). A recent re-evaluation of VLF2 stability (NewFields, 2019) included a review of publicly <br /> available information regarding the seismic hazard at the site using the United States Geologic <br /> Survey (USGS) interactive deaggregations tool. The peak ground acceleration (PGA) for the site <br /> was referenced as 0.14g for the 2,475-year-return seismic events with a mean earthquake <br /> magnitude of 5.5 at a distance of approximately 20 miles from the site. The USGS seismic hazard <br /> report is included in Appendix A. <br /> Based on the available information, we recommend the VLF2 be designed for both operations <br /> and closure considering an earthquake equal the 2,475-year return event. <br /> 3. SITE SUBSURFACE CONDITIONS <br /> 3.1. Site Investigation <br /> In support of the VLF2 Phase 3 Expansion,a geotechnical investigation was conducted on July 22, <br /> 2019 to meet the following objectives: <br /> > Characterize and evaluate the subsurface soil and rock materials to a maximum depth of 65 <br /> feet below the footprint of the proposed expansions; <br /> r Develop strength characteristics of the subgrade materials for facility design; and <br /> ;- Assess site subsurface material characteristics to determine their suitability for use as <br /> construction materials <br /> Page 4 <br />