EGL Ref: 8983 23 June 2022 Page 25 WAI-985-000-REP-LC-0004_Rev0.docx This report shall only be read in its entirety. • Undercut and backfill of sensitive rhyolite tuff material up to 20 m deep in the ‘Paleo Gully’ • Stripping the site of topsoil • Targeted stripping of ashes and alluvial soils • Undercut to rhyolite rock at and construction of the Upstream Cutoff Drain, Initial Toe Drain, and Downstream Toe Drain • Construction of subsoil drains up the gullies • Construction of the Zone A Pad • Construction of the Perimeter Embankment, including Perimeter Access Road, Perimeter Surface Water Drain, Subsurface Drain Collection Sumps and Closure Gravity Outlets • Construction of the Storage 3 Collection Pond including Decant, Power, Water Return and Closure Gravity Outlet pipes • Construction of the Leachate Collection Drains and Collection Sumps • Construction of the Perimeter Collection Sumps, including gravity collector pipes and pumps • Construction of the Initial embankment • Construction of the Impoundment Earthfill and Geomembrane Liner up to RL135 • Installation of the Tailings Delivery Pipe and Spigots • Installation of the Tailings Impoundment Decant, Power and Water Return Pipes. After the initial embankment is established, raising of the crest and the impoundment lining is a progressive task of fill placement, instrumentation installation, and rehabilitation. Storage 3 and Storage 1A can be constructed independent of each other. Figures 19 and 20 show the progressive development of the embankment up to RL145 and RL155 respectively. The volume of material to be excavated from the foundations of the embankment is summarised in Table 3. For the preliminary design an initial estimate of fill volumes by NAF, PAF and topsoil and by embankment zonation has been made and is summarised in Table 4 and Table 5. Approximately 2,650,000m3 of NAF is required. It is estimated that 1,000,000m3 can be obtained from stripping of the Storage 3 foundations and that 1,650,000m3 of NAF mine overburden material will be required from GOP and MOP. Management of NAF stockpile volumes is required to ensure suitable quantities of ash, alluvium and rhyolite is won from the Storage 3 site prior to the construction of the embankments. Material required to be sourced offsite from external suppliers, such as drainage metal, sand filter material, rockfill lining, pipes, sumps, concrete, and decants is summarised in Table 6. An Erosion and Sediment Control Report has been prepared by Southern Skies for Storage 3 (Ref. 20).
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