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0 ameo <br />Remediation for laterals and adits consisted of drilling nominal 3-inch diameter blast holes <br />into the crown pillar (the rock between the ground surface and the roof of the working) using <br />a pneumatic-hammer track drill rig. The blast holes were loaded and the crown pillars <br />blasted into the mined void. For some of the shallower workings, the blasted material was <br />excavated and replaced with a compacted fill. For deeper blasted laterals that could not be <br />fully and safely excavated, two or three layers of geogrid separated by a layer of SSF was <br />placed a minimum of fifteen feet beyond the mine working limits. <br />All blast holes that did not intercept the underground working or were not incorporated in the <br />blast were completely grouted with bentonite slurry prior to blasting the crown pillar and <br />remediating the working. <br />Underground working remediation activities for the Phase 5 VLF were performed from <br />February 2009 through June 2010. <br />2.2 Underdrains <br />2.2.1 Primary Underdrain <br />Ames constructed approximately 3,102 linear feet of Primary Underdrain in the Phase 5 <br />PSSA. Record Drawing No. 2 shows the location of the Primary Underdrain. The <br />cross-sectional dimensions of the Primary Underdrain were a nominal 5 feet wide by 3 feet <br />deep, providing a cross-sectional area of 15 square feet, as shown on IFC Drawing A260. <br />Ames excavated the Primary Underdrain trench to the minimum dimensions, and placed <br />geotextile and OF in the trench. Ames placed SSF over the geotextile to a minimum depth of <br />6 inches. The Primary Underdrain geosynthetic installation is discussed further in Section 3.1. <br />Approximately 1,723 cubic yards of UF, 287 cubic yards of SSF, 3,102 lineal feet of 6" CPe <br />perforated pipe, and 49,632 square feet of geotextile were used to construct the Primary <br />Underdrain. The Primary Underdrain is sloped at a minimum of one percent south beneath the <br />PSSA and south toe berm. The Primary Underdrain was routed to discharge into the Phase IVa <br />VLF, instead of constructing a dedicated sump. <br />• <br />AMEC Earth & Environmental, Inc. <br />2000 S. Colorado Blvd 2-1000 <br />Denver, CO 80222 <br />Tel 303-935-6505 <br />Fax 303-935-6575 www.amec.com <br />12