B-1 - Area 1, Coromandel Forest Park – Assessment of Environmental Effects 70 A collective of both New Zealand and international experts has been engaged to provide advice on the potential dewatering effects of the proposed activities and how to manage them to achieve that outcome. The output of that work are reports by GWS Limited (2022), Valenza (2022) and FloSolutions (2022) which are provided in Part H of these application documents. A summary of the key conclusions of those reports is provided below. 5.3.1 Effects on Ground and Surface Water Due to Construction of the Dual Tunnels The Dual Tunnels will be driven from the connection with the Willows Access Tunnel at Area 2 outside the CFP to the WUG at depths ranging from 150 m to 480 m below ground level within andesite. The andesite is the same rockmass present elsewhere in Waihi and will have a similar response to dewatering in that area insofar as it will be limited to areas immediately adjacent to the tunnels. No effects are expected in the near surface groundwater or on surface waters. There are some locations where inferred structural features will be driven through and these may need to be sealed to prevent groundwater ingress. Valenza (2022) describes how this will be done using methods commonly applied for this type of tunnelling activity in areas where groundwater ingress is expected. They include: Using conceptual modelling to identify areas where groundwater inflows into the Dual Tunnel will likely occur and at what rate; Conducting a minimum of one diamond core drilled hole sufficiently in advance of the tunnel face to assess geotechnical and hydrogeological conditions and evaluate where and what type of grouting or alternative mitigation measures wil l be required to manage groundwater inflows; Conducting additional probe hole drilling ahead of the Dual Tunnel development face to confirm the groundwater ingress conditions; Having available, when required, the equipment and suitably qualified and experienced personnel to conduct appropriate monitoring, and testing, implement grouting or alternative mitigation measures; and Assembling and adhering to suitable Trigger Action Response Plans so that grouting or alternative methods of mitigation to control groundwater ingress occurrences are suitably adapted to address any deviations from expected conditions in a way and at a rate which allows timely action to be taken. By implementing these measures no measurable effects on surface water bodies in the CFP will occur. Nor will soil moisture conditions in the regolith change so plant growth will not be adversely affected.
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