GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 95 5.1.2 Summary of proposed activity The proposed TSF3 will be an earth and rockfill embankment structure, like TSF1A and 2, forming an impoundment to store the discharged tailings slurry pumped from the Processing Plant. At its northern extent, the TSF abuts the steeply sloping hillside, comprising rhyolite and its western extent abuts TSF1A (Figure 5.3). The proposed TSF3 is described in detail in the TSF3 geotechnical report prepared by EGL (2021b). A plan of proposed TSF3 at 1,155 mRL is provided in Figure 5.3 (below). Figure 5.3 TSF3 layout plan to 1,155 mRL (EGL, 2021b) A summary of the key aspects as it relates to this assessment is provided below, with references to relevant plans in the EGL (2021b) TSF3 technical report provided in italics: – Foundation works: Removal of topsoil and stockpiling (EGL TSF3 Figure 16). Drainage works to intercept groundwater flow immediately beneath the impoundment (subsoil drains installed up the centre of the gullies, initial embankment upstream cutoff drain and initial toe drain, and a main embankment downstream toe drain) (EGL TSF3 DWG 620). Diversion works (including a section of the Ruahorehore Stream) (EGL TSF3 DWG 511). Initial excavation and dewatering of compressible soils. Up to 20 m of weak compressible soil in the paleo-gully area will require removal and backfill with NAF structural fill (EGL TSF3 DWG 516) Construction of a low-permeability NAF soil liner (Zone A material) across the tailings footprint (EGL TSF3 DWG 512-520). Installation of leachate collector drains above the Zone A liner, within the embankment (EGL TSF3 DWG 626). – Starter embankment - refer to EGL TSF3 (2021) Figure 18 and DWG 511: Construction of the starter embankment to 1,135 mRL using rock from Martha Phase 4 mining activities. Emplacement of HDPE liner to 1,135 mRL.
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