GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 122 Table 5.12 Actual and predicted groundwater quality concentrations (mg/L) Parameter Existing water quality at TSF3 (AP01 median values) Predicted values after mixing from TSF3 seepage* Existing groundwater quality after mixing at TSF1A and TSF2 (MW02 and MW06 median values) Operational to closure Long-term (post-closure) Al 0.004 0.004 - 0.005 0.03 - 0.1 0.009 - 0.01 As <0.001 0.003 - 0.01 0.004 - 0.01 0.001 Ba 0.08 0.06 - 0.07 0.04 - 0.07 0.1 - 0.2 Ca 1.1 2 - 7 21 - 98 6.4 - 6.6 Cd <0.00005 <0.0001 0.00009 - 0.0003 0.00008 - 0.0001 Co <0.0002 0.003 - 0.01 0.02 - 0.08 0.0004 - 0.005 Cr <0.0005 0.002 - 0.008 0.003 - 0.01 < 0.0005 Cu <0.0005 <0.0005 0.0008 - 0.002 0.0007 - 0.001 Fe <0.02 0.8 - 3.6 4.4 - 22 0.04 - 21 Hg <0.00008 <0.0001 <0.0001 0.0001 K 3.0 3.6 - 5.8 4.2 - 9.1 3.3 - 3.9 Mg 0.5 0.8 - 2.0 5.2 - 24 4.0 - 4.5 Mn 0.0009 0.1 - 0.6 0.7 – 3.6 0.1 - 1.9 Na 10 24 - 75 30 – 110 9.3 - 12 Ni <0.0005 0.0007 - 0.001 0.003 - 0.01 0.001 - 0.002 Pb <0.0001 0.0003 - 0.0008 0.0003 - 0.001 0.0003 - 0.001 SO4 5.0 31 - 128 95 - 452 10 - 22 Sb <0.0002 <0.0002 0.0002 - 0.0003 0.0004 - 0.0006 Zn 0.003 0.002 - 0.003 0.004 - 0.009 0.003 - 0.01 * Ranges are provided based on a range of groundwater flows, from direct mixing beneath the TSF to full mixing prior to discharge to the Ohinemuri River. The larger values are expected to be encountered closest to TSF3. Influence on surface water quality – Ohinemuri River As noted in Section 5.3.5, the Ohinemuri River is considered to form the primary environmental receptor for TSF3 discharges. The duration of the TSF3 operation is expected to be short relative to travel times for contaminants in groundwater to receiving surface water. The predicted water quality values are presented in Table 5.13 for the TSF3 operational/closure and long-term stages under steady-state conditions. Values for the starter embankment are not provided, for the reason noted above. The values presented are based on only on mixing and dilution of the TSF3 seepage from the tailings and embankment rock infiltration; no further groundwater dilution or attenuation is allowed for. The results indicate that: – Dilution in the Ohinemuri River is significant. Any increases predicted (as denoted by “” in Table 5.13) are so minor that they are unlikely to be detected within laboratory analytical margins of error. – The RWQC are not expected to be exceeded. – The mass flux leaving the TSF3 and expected to enter the Ohinemuri River is provided in Table 5.14. These values are presented for inclusion in the Water Management Report for the assessment of cumulative effects to the Ohinemuri River catchment and are not discussed further in this report.
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