EGL Ref: 9018 22 June 2022 Page 3 WAI-985-000-REP-LC-0006_Rev0.docx This report shall only be read in its entirety. the north and south, as their titles suggest. The construction of Storage 1A followed in 1998. The Southern Stockpile was covered by the construction of Storage 1A and the existing Central Stockpile (Figure 3). As part of the expansion works associated with Storage 1A the Northern Stockpile was expanded to its current footprint. From 2000, hard ignimbrite rockfill was separately stockpiled in the Eastern Haul Road Stockpile behind Storage 2. This stockpile is often called the Ignimbrite Stockpile (Figure 3). The purpose of the stockpile is to separate out the non-acid forming (NAF) ignimbrite rockfill from the finer NAF fill placed in the Northern Stockpile. Ignimbrite rockfill is used for the wearing and base course layers in the haul roads and as a NAF fill for closure capping of the tailings. Topsoil stockpiles (Figure 3) remain around the toe of the Northern Stockpile, Storage 2, and Storage 1A. The Polishing Pond Stockpile located at the Processing Plant and Water Treatment site (Figure 3) is also engineered to store PAF material. The Polishing Pond Stockpile has subsoil drainage installed below a low permeability earthfill pad (0.6m thick of Zone A). Leachate drains are installed on top of the liner at the toe of the stockpile. It was originally constructed in 2006 and used to store ore. Since 2020 the Polishing Pond Stockpile area has been used to temporarily stockpile material to be used as backfill for the underground mines. The topsoil stockpiles and the Polishing Pond Stockpile are temporary stockpiles and will not remain in closure. 2.3. Current stockpiles The focus of this report is the three main large stockpiles at the Development Site. NAF and PAF materials are separately stockpiled for use in different embankment zones. The Northern Stockpile is used only for NAF. Central and East Stockpiles are setup to receive PAF. However, if required they can be used to stockpile NAF. The Northern Stockpile (Figure 3) does not have a Zone A base pad and is only now used for NAF material. The stockpile does have some subsurface leachate drains to collect seepage from PAF material placed at the toe of the Storage 2 embankment. Ignimbrite rock was placed as a toe bund around the perimeter of the Northern Stockpile to manage wet materials placed in the stockpile. The ignimbrite toe bund has been partly removed for use elsewhere onsite. The Northern Stockpile is to be replaced by the NRS. The Central Stockpile has subsurface drains, a Zone A base pad and leachate drains. The surface runoff reports to Collection Pond S3 via an open channel drain down the rehabilitated embankment face. The East Stockpile is lined with a Zone A pad. This pad was placed over the Surplus Soil Stockpile to allow stockpiling of PAF material. An ignimbrite rockfill toe bund was constructed to ensure the stability of the East Stockpile. Leachate and subsoil drains collect seepage from the stockpile. The surface water runoff reports to Collection Pond S5 with overflow draining to Collection Pond S4 via the Perimeter Drain.
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