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June 24, 2003 -11- 003-2203.7 <br />• Shallow surface pits that were less than 25 feet deep below the final SLF <br />subgrade surface were excavated to bedrock or pit termination. The pits were <br />then backfilled with compacted SSF and SF to the final subgrade elevation, <br />• In some cases, shallow surface pits were completely removed during slope <br />re-contouring and required no further remediation. <br />2.1.2 Remediation of Laterals/Inclines/Adits <br />Laterals and adits identified within the Phase Nb PSSA were remediated accordingly per the <br />approved remediation specifications. Underground workings that were identifed within 50 feet of <br />the finished grade elevation were remediated. Workings that were deeper than 50 feet below the final <br />grade elevation did not require any remediation. <br />Remediation For laterals and adits consisted of drilling nominal 3-inch diameter blast holes into the <br />crown pillar (the rock between the ground surface and the roof of the working) using an <br />Ingersoll-Rand EMC-660 pneumatic-hammer track drill rig. The blast holes were loaded and the <br />crown pillars blasted into the mined void. For some of the shallower workings, the blasted material <br />was excavated and replaced with a compacted fill. For deeper blasted laterals that could not be fully <br />and safely excavated, two layers of geogrid separated by a layer of Select Structural Fill were placed <br />15 feet (laterally) beyond the mine working limits. <br />All blast holes that did not intercept the underground working or were not incorporated in the blast <br />were completely gouted with bentonite slurry prior to blasting the crown pillar and remediating the <br />working. <br />Underground working remediation activities for the Phase Nb PSSA were performed from October <br />2001 through August 2002. <br />2.2 Underdrains <br />2.2.1 Primary Underdrain <br />Ames constructed approximately 2,650 linear feet of PU in the Phase Nb PSSA. Record Drawing <br />No. 2 shows the location of the PU. The cross-sectional dimensions of the PU were a nominal 5 feet <br />wide by 3 feet deep, providing across-sectional area of 15 square feet, as shown on IFC Drawing 13, <br />^~oouzono+oo~+ic~rtrsseaws~aonzzw.o+oo.o»+an~o~m~ Golder Associates <br />