SECTION 3 Dual Access Tunnels C:\D Data\GWS C Drive\GWS\Client Files\1344 OGL - WKP\4 Deliverables\WUG Effects Summary\June 2022\WNP Groundwater Effects Summary_Final_Rev_0.docx 12 3.3 Hydrologic and Hydrogeologic Setting The geology along the alignment is generally monolithic being within post mineralisation andesite. Some structures are expected to be intercepted during tunnelling and any inflows via these features will be grouted off as the tunnels advance. The dual tunnels are mostly within the Otahu surface water catchment, but a portion to the south is within the Waihou Catchment (Waihi Basin). 3.4 Summary of Effects Groundwater Inflows The rock mass inflows from tunnelling have been calculated using an Excel spreadsheet that applies the Perrocet (2005) method for calculating tunnel inflows. Added to the rockmass inflows are the inflows from vent shafts (derived using SEEP/W) and from geologic structures (analytical equation) to provide total groundwater inflows. In summary, in the order of 9,200 m3/d is expected to be generated through driving the dual tunnels to the Wharekirauponga mine. This water will report back to Waihi for treatment and disposal then discharge. This volume does not include lateral development once the tunnels reach the mine. Drawdown Extent No ongoing groundwater drawdown effects are expected due to the low rockmass permeability of the andesite and given any zones of higher inflows will be sealed off. As a result, no effects are expected in the near surface due to development of the dual access tunnels. Other Effects Related to the Take Given the absence of drawdown effects associated with development of the tunnels, no effects are expected on surface waters, other groundwater users, plant growth, other aquifers or water quality. Effect on Water Quality Once the tunnels are no longer required rewatering will occur and the groundwater system will return to its previous state. Some groundwater will come into contact with the cement grout and backfilled wasterock, however this is not expected to change the overall quality in the aquifer due to the limited contact area relative to the system throughflow. This statement is similarly applicable to the vent shaft following construction. In summary, no adverse effects on groundwater and therefore surface water quality are expected from the tunnels while dewatered or following closure. Monitoring No monitoring is proposed over the length of the dual access tunnels due to the absence of any associated measurable effect on surface or groundwaters.
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