B-1 - Area 1, Coromandel Forest Park – Assessment of Environmental Effects 71 Given the depth of the Dual Tunnels and mitigating construction methodology, no groundwater monitoring is deemed necessary, nor is proposed over the alignment. 5.3.2 Effects on Ground and Surface Water due to the Wharekirauponga Underground Mine Exploration drilling and mapping of the Wharekirauponga deposit has provided a significant database of geological and geotechnical information that provides a detailed characterisation of the mineralised structures and host rocks. Extrapolation of the hydrologic and hydrogeologic testing data collected has enabled a Conceptual Groundwater Model (“CGM”) to be developed that provides the basis for understanding what effects, if any, might occur from the proposed dewatering of the orebody at the WUG. Preliminary numerical groundwater modelling has been undertaken based on the understanding of the CGM to make predictions of how the groundwater systems will react to dewatering of the veins. At a catchment scale, the CGM concludes that where post mineralisation Andesite is present, a shallow groundwater system is also present and dewatering effects from the underlying rockmass do not propagate to the surface. That is because the Andesite has a naturally low permeability that retains infiltrating water and there is a weathering profile on the surface of the underlying rocks that limits the ability for shallow groundwater to move downward. Where Andesite is present at the surface, streams are perched on these units and are not in contact with the deeper groundwater system, meaning no effects on surface water can take place from deep dewatering in those rocks. It is only where Rhyolite rocks are present in the near surface, where the shallow and deeper groundwater systems are connected, that dewatering effects have the potential to develop. If deep dewatering effects affect the shallow groundwater system, the potential to affect surface water flows exists. Valenza (2022) describes how the mining in this area will be managed to ensure it causes no measurable effect on surface water bodies using methods commonly applied to mine areas where groundwater ingress is expected. Key aspects of the management response will be: Installation of monitoring instruments and hydraulic testing in zones of potential impact in advance of mining; Where suitable and necessary, undertaking pre-development grouting and depressurisation of the upper sections of stopes or other zones of groundwater connectivity before mining; Assembling and adhering to suitable Trigger Action Response Plans during predevelopment grouting activities so that methods of mitigation to control groundwater
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