GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 61 within the water management system. These sources include processing plant (and WTP) area runoff, groundwater inflows from the WUG, and seepage / RS runoff (via collection ponds). The model identifies periods from 2027 onwards where excess flows are unable to be discharged under the existing consented regimes due to low flow restrictions in the Ohinemuri River which predominantly occur during the summer months. The frequency and volume of these excess flows is tied closely to the development of the Wharekirauponga Underground Mine. In this regard, the key reason for the modelled excess is the assumed rates for dewatering of the Wharekirauponga Underground Mine. The actual rates of dewatering will be better understood well in advance of 2026 before the potentially critical period (as modelled) is reached. The WBM model currently directs these excess flows to the active TSF ponds for storage. Alternative operational solutions could consist of one or a mixture of the following operational options: Excess flows sent to the operational TSF (default option presented in the WBM) Dewatering of MUG/WUG temporarily suspended Scheduling changes or amendments Potential future alternative discharge options In addition, the reduction in the treatment of collection pond water may also be possible by 2026 – associated with upstream catchment rehabilitation and conversion to silt ponds as has occurred historically. None of these options (apart from direction of the excess flows to the operational TSF) are explicitly modelled here. To decrease the risk of excess Priority One waters during peak development and low summer flow periods, the WTP operation will need to maximise the treatment of non-Priority oOne waters when the WTP capacity and river flows allow. Figure 44 WTP Mean Monthly Excess Flow (High K Scenario)
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