Oceana Gold Waihi North Project Waihi North Project Geochemical Assessment – Geochemistry of Tailings and Overburden, Treatment and Mitigation Revision 0 – 17-Jun-2022 Prepared for – Oceana Gold (New Zealand) Limited – Co No.: 2274246 34 AECOM Table 17 Existing Groundwater Quality Within the WUG System Parameter Existing WUG Groundwater Waihi No.7 Shaft Premining Predicted Favona Backfill Water Quality Min Median Max 1984 Unmitigated Mitigated 84.5 m depth 206.5 m depth pH(pH units) 5.2 6.3 7.4 6.5 6.9 6.9 [3.2] 7.3 [5.5] Alkalinity - Total (g/m3 as CaCO3) 3.7 32.5 300 - - - - Sulphate(g/m3) 5 7.5 200 550 1200 1020 500 Aluminium-Dissolved(g/m3) 0.003 0.011 0.62 - - 0.001 [55] 0.001 [27] Arsenic-Dissolved(g/m3) 0.001 0.00135 0.035 0.017 0.05 0.12 [6.4] 0.04 [3.1] Antimony-Dissolved(g/m3) 0.0002 0.0002 0.0045 - - 0.001 0.0004 Calcium-Dissolved(g/m3) 0.36 6.8 121 545 391 320 [48] 170 [23] Cadmium-Dissolved(g/m3) 0.00005 0.00005 0.00005 - - - - Copper-Dissolved(g/m3) 0.0005 0.0009 0.011 < 0.001 < 0.001 1.1 0.55 Iron-Dissolved(g/m3) 0.02 0.295 24 7.9 11.3 150 [180] 38 [90] Magnesium-Dissolved(g/m3) 0.57 1.535 17.2 67 172 31 15 Manganese-Dissolved(g/m3) 0.004 0.2595 1.24 18.2 21 - - Lead-Dissolved(g/m3) 0.0001 0.0001 0.0034 < 0.005 < 0.005 0.0001 [0.001] 0.0001 [0.0003] Nickel-Dissolved(g/m3) 0.0005 0.0024 0.0173 - - 0.09 [0.15] 0.01 [0.07] Potassium-Dissolved(g/m3) 1.1 5 14.3 11 14.1 14.2 7 Sodium-Dissolved(g/m3) 5.7 9.2 70 26 49.7 8.4 4 Zinc-Dissolved(g/m3) 0.0022 0.0144 1.09 1.32 0.4 1.8 [3.7] 1.8 Note: The values in brackets represent the worst case backfill water quality predictions
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