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October 2004 -10- 043 -2170 <br />2.1.2 Remediation of L,aterals/Inctines/Adits <br />Laterals and adits identified within 50 feet of finished grade in the Phase 1Vc OSA were remediated <br />according to approved remediation specifications. Workings that were :deeper than 50 feet below the <br />final grade elevation did not require any remediation. <br />Remediation for laterals and adits consisted of drilling nominal 3 -inch diameter iblast.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. If the blasted lateral or adit could not be fully and safely <br />excavated, two layers of geogrid separated by a layer of Select Structural Fill was placed 15 feet <br />(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 grouted with bentonite slurry prior to blasting the crown pillar and remediating the <br />working. <br />41 Underground working remediation activities for the Phase We OSA were performed during the <br />construction seasons from July 2001 through June 2004. <br />2.2 Underdrains <br />Ames constructed approximately 1,348 linear feet of Secondary Underdrain (SU) in the Phase IVc <br />OSA. Record Drawing No. 2 shows the location of the SU. The cross - sectional dimensions of the SU <br />was nominally 4 feet wide by 2 feet deep, providing a cross - sectional area of 8 square feet, as shown on <br />1FC Drawing 13, Detail 2. Ames excavated each SU trench to the minimum dimensions, and placed <br />. geotextile and OF in the trench. Ames placed SSF over the geotextile to a mui =' 'um depth of 6 inches. <br />The SU geosynthetie installation is discussed further in Section 3.1. Approximately 400 cubic yards of <br />UF, 100 cubic yards of SSF, and 17,500 square feet of geotextile were used to construct the SU. <br />2.3 Leak Detection System <br />Ames constructed approximately 6,560 linear feet of LDT and 745 linear feet of LDT extension in the <br />• Phase IVe OSA, at the location shown in Record Drawing No. 4. <br />lft%SM17019MCUO -QA LVa106n6422170.04M121MC lPhWedw Golder Associates <br />