2014-02-07_REPORT - M1980244 (7)

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Cripple Creek & Victor Gold Mining Company Mill Site Earthworks Project Final Report Quality Assurance Monitoring & Test Results January 31, 2014 R1 4ft W?Vr416 • For open workings the excavations were backfilled with CSB to approximately 10 feet below the finished surface grade. The surface of the CSB was compacted using the shovel from a CAT excavator. A minimum 3- foot -thick concrete plug was cast into the shaft and allowed to cure for a minimum of 7 days. A minimum 7 -foot- thick layer of cemented rockfill was then placed onto the concrete plug. SF was then placed to the final grade, as needed. In some cases, the excavation did not require placement of CSB prior to placement of the concrete plug and cemented rockfill. • For collapsed workings, collapsed materials were excavated to a depth of 25 feet below finished grade. The excavations were either backfilled with CSB to approximately 3 feet below the soil /bedrock interface or shaped for placement of a concrete plug. The surface of the CSB was compacted using the shovel from a CAT excavator. A minimum 3- foot -thick concrete plug was cast into the shaft and allowed to cure for 7 days. A minimum 7- foot -thick layer of cemented rockfill was then placed over the concrete plug. After the cemented rockfill was allowed to cure, SF was then placed to the final grade, as needed. • Shallow surface pits that were less than 25 feet deep below the final SLF subgrade surface were excavated to bedrock or pit termination. The pits were then backfilled with compacted SSF and SF to the final subgrade elevation. • In some cases, shallow surface pits were completely removed during slope re- contouring and required no further remediation. 2.1.2 Remediation of Lateral /Inclines /Adits A number of laterals and adits were identified within the Mill Site Earthworks footprint. Per the remediation recommendations, underground workings were identified within 50 feet of the existing grade elevation were remediated. Workings that were deeper than 50 feet below the final grade elevation were not remediated. Remediation for laterals and adits consisted of drilling nominal 3- inch - diameter blast holes into the crown pillar (the rock between the ground surface and the roof of the working) using a pneumatic hammer track drill rig. The blast holes were loaded and the crown pillars blasted into the mined void. For some of the shallower workings, the blasted material was excavated and replaced with compacted fill. For deeper blasted laterals that could not be fully and safely excavated, three layers of geogrid separated by a layer of Select Structural Fill was placed 15 feet beyond the mine working limits. All blast holes that did not intercept the underground working or were not incorporated in the blast were completely grouted with bentonite slurry prior to blasting the crown pillar and remediating the working. Underground working remediation activities for the Mill Site Earthworks Project were performed from December 2011 through July 2012. 8