GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 75 Table H.7 Predicted leachate flow to Ohinemuri River within groundwater Infiltration conditions Leachate flow to Ohinemuri River (m3/day) Operational scenario 30% rainfall 71 50% rainfall 97 Closure scenario 5-year average cap infiltration (369 mm/year)2 49 H.2.4 Water quality assessment results As presented in Table H.5, approximately 262 m3/day of rock stack leachate is predicted to seep through the Zone A liner in the NRS closure scenario. A large proportion of this leachate is then predicted to be captured by the subsoil drains (Table H.6), with the remaining 49 m3/day then anticipated to flow west towards the Ohinemuri River within the shallow groundwater system (Table H.7). Table H.8 presents the predicted water quality beneath the NRS following mixing and equilibration of the groundwater with leachate seepage through the Zone A liner in the NRS closure scenario, and the predicted water quality following mixing with the Ohinemuri River. Table H.8 Predicted receiving water quality in the NRS closure scenario (values in mg/L) Parameter Existing shallow groundwater quality (DH05a median) Predicted values after equilibration of NRS leachate with shallow groundwater Existing Ohinemuri River quality (OH3 median) Predicted values after mixing with Ohinemuri River Receiving water quality criteria pH 6.5 7.4 7.2 - Al 0.003 0.011 0.013 0.013 As 0.0096 <0.001 <0.0010 <0.0010 0.19 Ba 0.67 0.02 0.027 0.027 Ca 2.7 116.0 3.1 3.6 Cd <0.00005 0.000010 <0.00005 <0.000050 0.0003 Co 0.041 0.020 <0.00020 0.00028 Cr <0.0005 <0.0005 <0.0005 <0.00050 0.01 Cu <0.0005 0.000060 <0.0005 <0.00050 0.003 Fe 6.8 21.0 0.10 0.19 1 Hg <0.00008* <0.00008* <0.00008* <0.00008* 0.000012 K 2.3 3.0 2.0 2.0 Mg 1.2 28.0 1.9 2.0 Mn 1.5 4.0 0.010 0.027 2 Na 9.9 11.0 9.2 9.2 Ni 0.0051 <0.003 <0.0005 <0.00051 0.04 Pb 0.00016 <0.0001 <0.0001 <0.0001 0.0004 SO4 5.0 338.0 5.0 6.4
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