GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 53 Figure 35 Modelled Median Total Flow to Waihi WTP (Low K Tunnel Inflow) It has been calculated that the combined storage and pump capacity for the collection ponds are insufficient to manage the pond water levels when the WRS increases in size to an area of approximately 3 Ha. In these circumstances overflow is possible, however where the modelled 24 hr rainfall records are applied, overflow events from the collection ponds are predicted to occur only during the most extreme rainfall events (with an approximate return period of 10 years). Untreated water will discharge directly to the Mataura Stream. 6.2.2 Mataura Stream Water Quality The Mataura Stream is considered to form the primary environmental receptor within the WSFA. No mine water impacts (except a small volume of uncaptured WRS seepage) are expected based on the assumed infrastructure within the WSFA. WUG groundwater will be pumped and piped directly to the WTP at Baxter Road and collected runoff and seepage from the WRS will undergo similar transport via storage in the WRS collection pond. The predicted impact is detailed in GHD (2022) and is conservatively based on the maximum constructed height and extent of the WRS, no groundwater dilution or attenuation. The results are presented in Table 13 and illustrate an expected minimal impact on receiving water quality. Table 13 Mataura Stream water quality Mataura (Existing) Mataura (Modelled Data) Consented Receiving Water Quality# Chemical Parameter Median Median Max Hardness 20 g/m3 CaCO3 Hardness 100 g/m3 CaCO3 Iron (g/m3) 0.04 0.04 0.2 1.0 1.0 Manganese (g/m3) 0.003 0.0035 0.5 2.0 2.0 Copper (g/m3) < 0.0005 < 0.0005 < 0.0005 0.003 0.011
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