GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 123 The predicted concentrations of mercury are greater than the RWQC as the laboratory detection limit of this parameter is greater than the criterion. Mercury is typically immobile in groundwater due to volatilisation and/or precipitation processes and has not been reported in significant, persistent concentrations by OGNZL (2020). The effect of changes to surface water quality resulting directly from TSF3 groundwater discharges is therefore considered to be negligible. Review of water quality predictions in the context of the impacts on groundwater from TSF1A and TSF2 operation is provided below to support the interpretation. Table 5.13 Ohinemuri River water quality (values in mg/L) Parameter Existing water quality (OH1 median values) Predicted water quality Receiving water quality criteria Operational to closure Long-term (postclosure) Al 0.03 0.03 0.03 As <0.001 <0.001 <0.001 0.19 Ba 0.03 0.03 0.03 Ca 42 42 42 Cd <0.00005 <0.00005 <0.00005 0.0003 Co <0.0002 <0.0002 <0.0005 Cr <0.0005 <0.0005 <0.0005 0.01 Cu <0.0005 <0.0005 <0.0005 0.003 Fe 0.15 0.2 0.2 1.0 Hg <0.00008* <0.00008* <0.00008* 0.000012 K 3.4 3.4 3.4 Mg 3.5 3.5 3.6 Mn 0.015 0.02 0.05 2.0 Na 14.5 14.6 14.7 Ni <0.0005 <0.0005 <0.0007 0.04 Pb <0.0001 <0.0001 <0.0001 0.0004 SO4 145 145 146 Sb <0.0002 <0.0002 <0.0002 0.03 Zn 0.0013 0.0013 0.0014 0.027 Notes: Receiving water quality criteria values for hardness 20 g/m3 CaCO3 Values in bold indicate an exceedance of the receiving water quality criteria * The mercury (Hg) criterion is lower than available laboratory detection limits Denotes a predicted increase from existing surface water quality Table 5.14 Mean predicted mass flux (kg/day) from TSF3 to the Ohinemuri River Parameter Operational to closure Long-term (post-closure) Al 0.0004 0.02 As 0.001 0.002 Ba 0.001 0.002 Ca 1.0 16 Cd 0.00002 0.00004
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