GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 64 . Parameter Existing shallow groundwater quality (GLD04s) Predicted values after equilibration of TSF discharge with shallow groundwater (AECOM, 2021b) Existing Ohinemuri River quality (OH6 median) Predicted values after mixing with Ohinemuri River Receiving water quality criteria Ca 10.5 79 43.5 43.8 Cd <0.00005 0.0001 <0.00005 <0.00005 0.0003 Cl 9 11 16.4 16.4 Co 0.017 0.04 0.0009 0.0011 Cr <0.0005 <0.0005 <0.00050 <0.00050 0.01 Cu 0.0014 0.0008 0.0005 0.00050 0.003 Fe 0.03 2.2 0.09 0.098 1 Hg <0.00008* 0.00011 <0.00008* <0.00008* 0.000012 K 3.5 6 3.6 3.6 Mg 2.8 12 3.1 3.1 Mn 0.43 1.5 0.019 0.024 2 Na 24 27 17.1 17.2 Ni 0.0089 0.007 0.0005 0.00053 0.04 Pb <0.0001 <0.0001 <0.0001 <0.0001 0.0004 SO4 17 263 148.0 149.0 Sb 0.0002 0.0007 0.00055 0.00055 0.03 Se <0.001 <0.001 <0.001 <0.001 0.02 Zn 0.13 0.12 0.0024 0.0028 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 groundwater / surface water quality 3.7 Gladstone effects summary and discussion The predicted influence on key environmental aspects is summarised in the following sections. 3.7.1 GOP excavation summary and discussion The key potential effects of the GOP excavation are a lowering of shallow groundwater levels locally, a reduction in flows to surface water and discharge of any dewatered groundwater to the receiving environment via the WTP. The potential effects and recommendations for management or monitoring are discussed below. Shallow groundwater It is anticipated that the shallow groundwater table will be intercepted during excavation of the GOP, with total inflows to the pit estimated to be low (approximately 9 m3/day under steady state conditions) due to the low permeability of the deposits (Table 3.8). This is considered to be minimal in the context of stormwater run-off. The complexity of the geology and topography adjacent to the pit means that the predicted dewatering ZOI is not radial. The dewatering of the shallow groundwater system is predicted to result in groundwater table drawdown of 3 m on the northern pit boundary, increasing up to 8 m on the southern pit boundary where the ZOI extends 290 m
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