GHD | Oceana Gold NZ Ltd | 12552081 | Geochemical Assessment Wharekirauponga Underground Mine (WAI985-000-REP-LC-0013) 28 Utilising this methodology, the predicted WUG tunnel inflow sulphate concentration was estimated at 535 mg/L and the predicted arsenic concentration of the leachate is estimated at a concentration of 0.036 mg/L (Table 3). The column derived arsenic concentration compares well with the derived arsenic concentration based on the 95th percentile Waihi dewatering data – 0.036 mg/L (Table 4). Calculated sulphate and arsenic concentrations based on conservative sensitivity parameters (Spoil NAPP concentration, tunnel roughness factor, oxidation profile depth, PAF fraction of tunnel exposed walls and inflow volume of water) are up to 1,817 mg/L and 0.125 mg/L respectively (Table 3) and likely represent the upper bounds of the tunnel and mine inflow water. Figure 20 Column sulphate / arsenic leachate relationship Table 3 Predicted sulphate and arsenic concentrations based on column sulphate generation rate *Based on assumed inflow and tunnel length as per GWS, 2022, but calculated oxidising volume and water inflow is proportional at any length #Highlighted values depict the sensitivities applied High Flow Low Flow High Flow High O2 prof ileHigh Flow High Flow High Flow med O2 prof ilemed O2 prof ilemed O2 prof ileHigh O2 prof ilemed O2 prof ilemed O2 prof ilemed O2 profile Mean Mean 95%ile Mean Mean Mean Mean NAPP Column mean H2SO4 25 33 33 33 33 33 33 33 NAPP Spoil mean H2SO4 18 24 24 24 24 24 80 NAPP Spoil 95%ile H2SO4 61 80 80 Length of tunnel* km 11 11 11 11 11 11 11 Tunnel Roughness Factor 5 5 5 5 10 5 10 Area per m m2 118 118 118 118 236 118 236 Total surface area m2 1,298,000 1,298,000 1,298,000 1,298,000 2,596,000 1,298,000 2,596,000 Oxidation Profile m 0.2 0.2 0.2 0.3 0.2 0.2 0.2 Total oxidising area m3 259,600 259,600 259,600 389,400 519,200 259,600 519,200 Vol of water* m3/day 12,076 6,650 12,076 12,076 12,076 12,076 6,650 Vol/tonne (in-situ) 2.1 2.1 2.1 2.1 2.1 2.1 2.1 Percentage PAF % 0.5 0.5 0.5 0.5 0.5 0.75 0.75 Tonnes of oxidising material t 272,580 272,580 272,580 408,870 545,160 408,870 817,740 Sulphate generation per day kg 6,464 6,464 21,942 9,696 12,928 9,696 65,825 SO4 concentration mg/L 535 972 1,817 803 1,071 803 9,899 As Concentration mg/L 0.036 0.055 0.125 0.047 0.061 0.047 296.453 Average Sulphate Generation Rate (mg SO4/kg/day) Sulphate Generation Rate (mg SO4/kg/day) Sensitivity
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