2012-08-24_REPORT - M1980244 (16)

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_ During topsoil stripping, an Underground Working was encountered. The working was given a number (UG #4042) by an AMEC representative and surveyed by Ames. Investigation of the working will be performed at a later date. B) Drilling Confirmatory drilling was performed at Underground Working #4000 using one track mounted drill rig. Two holes were drilled into the shaft to investigate if the shaft was "choked off" during coarse shaft backfill placement. Both holes indicated that the entire shaft was filled completely, to the bottom. An approximate total of 100 linear feet was drilled. As -built survey of the drill holes was performed by Ames. Confirmatory drilling was performed at Underground Working #4024. A drill pattern was set out by an AMEC field representative. Thirty eight holes were drilled encountering nine voids. An approximate total of 1,900 linear feet was drilled. As -built survey of the drill holes was performed by Ames. Grouting of missed (non -void) confirmatory drill holes was performed at Underground Working #4026. A grout pump and laborers were used to place bentonite grout into the "miss" drill holes. Confirmatory drilling was performed at Underground Working #4028. A drill pattern was set out by an AMEC field representative. Thirty one holes were drilled encountering eleven voids. An approximate total of 1,550 linear feet was drilled. As -built survey of the drill holes was performed by Ames. Confirmatory drilling was performed at Underground Working #4029. A drill pattern was set out by an AMEC field representative. Eighteen holes were drilled encountering nine voids. An approximate total of 900 linear feet was drilled. As -built survey of the drill holes was performed by Ames. Confirmatory drilling was performed at Underground Working #4031. A drill pattern was set out by an AMEC field representative. Thirty two holes were drilled encountering eighteen voids. An approximate total of 1,600 lineal feet was drilled. As -built survey of the drill holes was performed by Ames. Q Remediation Remediation of Underground Working #4000 was performed filling the shaft with coarse shaft backfill using a Hitachi 350 excavator. The shaft was filled within ten feet below the existing ground surface. When the shaft was filled to a level the excavator could reach, compaction of the material was performed with the excavator bucket. The shaft was not as deep as assumed and less material was used to the fill the shaft as intended. Two holes were drilled into the shaft to ensure that it was not "choked off' (see confirmatory drilling). Underground Working #4023 was investigated using a Hitachi 350 excavator and observation was performed by an AMEC field representative. Excavation of the area was performed and it was found to be a shallow surface working. The native material was found to be consistent and all signs of a significant working were removed. The working was backfilled with structural fill in 18" to 24" lifts using various CAT dozers. Each lift was moisture conditioned using a tandem axle water truck (when necessary) and compacted using a 10 -ton vibratory smooth drum compactor, passing over the entire fill surface at least 4 times (method compaction technique was applicable). MEW Weekly Report WE 01.28.2012