SECTION 2 Wharekirauponga Underground Mine 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 9 Figure 12 Extent of Near Surface Drawdown Effects (Flosolutions, April 2022) Effects on other Aquifers The primary aquifer that will be dewatered to access the mineralisation is the Rhyolite rockmass. Modelling and experience elsewhere have shown that while some extent of dewatering of the rhyolite rockmass will occur, it will be localised and will not affect water levels in any overlying aquifers such as the post mineralisation Andesite units. This is due to a confining layer formed by weathering and alteration that separates the two systems. During construction of the shafts, there will be some localised drawdown of the groundwater system. Following construction of the lined shafts the groundwater system will return to its previous state. Overall, effects on other aquifers due to the proposed dewatering is not expected. Effects on Surface Waters If dewatering of the Rhyolite rockmass in the near surface were to occur, there are a number potential mechanisms by which surface waters may be affected: • Losses through the base of the stream beds • A reduction in spring fed inflows from permeable structures • A reduction in spring fed inflows from springs at the stream headwaters • Regolith soil water loss The first 3 mechanisms listed remain the subject of ongoing work to ensure surface waters are not affected by underground mine dewatering using appropriate mitigation techniques. Regolith water will continue to discharge into the catchment and will be unaffected by dewatering as it is a function of climatic conditions and flows in the unsaturated zone above the permanent water table as shown in Figure 11.
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