GHD | Oceana Gold New Zealand Ltd. | 12552081 | Waihi North Project 48 Figure 29 Willows Rock Stack Development 6.1.1.2 WUG Groundwater Inflow The volume of groundwater flow entering the WUG access tunnel has been provided in GWS 2022 which presents two scenarios that consider the likely range of rock mass permeability ranging from 1×10-8 m/sec (high K scenario) to 5×10-9 m/s (low K scenario). The WBM utilises estimated groundwater inflows that are higher than those outlined in GWS 2022 and are based on previous versions of the groundwater assessment. The modelled volume is therefore considered conservative and it is likely that actual groundwater inflow rates will be less than utilised in the WBM. In addition, volumes of groundwater inflow for the WUG Mine, shafts and ore transport tunnel have also been provided. This data has been summarised into expected minimum and maximum scenarios which have been adopted within the WBM to assess the likely minimum and maximum groundwater inflows and resultant treatment requirements. Given the peak WUG flows are not expected until year four of development (presented as 2027 based on the nominal timeline), assumptions relating to groundwater inflow rates will be validated well in advance. The total assumed groundwater inflow within the WBM includes the following components: WUG access tunnel from the Willows Portal to the WUG orebody (up to 12,076 m3/day) WUG ore transport tunnel to Waihi (up to 3,183 m3/day) WUG Mine (up to 4,500 m3/day) WUG shafts (up to 2,500 m3/day) The summarised maximum and minimum assumed flows as utilised within the WBM are represented in Figure 30 and Figure 31 and are referred to as the high K and low K scenarios. As the WUG water inflow rate has a large influence of the WBM, both these upper and lower bound scenarios are utilised and reported within the WBM. Figure 30 Predicted Maximum Tunnel Inflow (High K)
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