GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 115 Figure 5.15 Groundwater flow paths for the key TSF3 scenarios 5.5.3 Embankment infiltration Rainwater that infiltrates through the embankment is expected to be influenced by the rock geochemistry. The predicted rates of infiltration through the embankment, to the receiving environment, are summarised in Table 5.8: – Starter embankment (1,135 m RL): As no capping layer is emplaced at this stage, rainfall has been applied at 35% of the average annual rainfall rate (740 mm/year; seepage face review). The resulting infiltration rate is 30% of rainfall (600 mm/year), which is expected to generate 230 m3/day of flow through the embankment. The remainder of applied recharge to the embankment is inferred to go to surface runoff and be captured by the surface drainage. As with the tailings discharge, all of the embankment infiltration at this stage is predicted to be captured by the TSF3 drain system and prevented from downward migration due to upward hydraulic gradients present beneath the toe of the embankment; this is illustrated by the flow lines in Figure 5.15. – Operational to closure (1,135 m RL): On closure, after the capping layers are emplaced (Zones G and H), an infiltration rate of 370 mm/year has been applied as infiltrating through into Zone D. This value has been applied in accordance with that derived by AECOM (2020) for the existing TSF1A. This value is approximately 20% of the applied rainfall and is predicted to generate 270 m3/day of water through the full embankment. All embankment infiltration is predicted to be captured by the drains for this scenario.
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