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 10 It can be stated with confidence that the Warm Spring will cease to flow until mining has ceased and rewatering of the mine has taken place. This constitutes a stream loss in the order of 3 L/s. Effects on Plant Growth Plant growth is dependent on regolith water and shallow groundwater. As no effects are expected to these systems as a result of mine dewatering, no effects on plant growth are expected either. Effects on Groundwater Users No effect on other groundwater users is expected given the absence of bores in the catchment, the distance of the take point and localised drawdown effects that will develop. Effects on Groundwater or Surface Water Quality During mining groundwater will be pumped back to the water treatment plant at Waihi and treated prior to discharge. During mining there will be no effect on groundwater quality. On completion of mining, the aquifer will cease being pumped and the natural groundwater system will be reinstated. Localised discharge of this water will return to natural discharge pathways once water pressures are re-established including at the warm spring location. The quality of the groundwater following mining will be determined by a number of factors including the chemistry of the backfilled materials, the amount of grout placed during mining and the amount of stabilisation required to neutralise the backfill. To some degree the final chemistry of the backfilled stope, and therefore the groundwater quality after interacting with it, can be managed through the selection of the backfill materials and chemical stabilization. Geochemical modelling is required to enable a prediction of the endpoint groundwater chemistry based on the aforementioned parameters and is still the subject of further studies at this time. Proposed Monitoring Combined surface water and groundwater monitoring is proposed and will be sufficiently robust that it can detect changes in groundwater-surface water interaction and inform mitigation actions if required. Surface water flows will be monitored at permanent gauging locations upstream and downstream of the mineralised zones to detect any potential baseflow losses through the bottom of the stream. In addition, vibrating wire piezometers will be installed at critical locations adjacent to the stream for ongoing monitoring to assess the vertical gradients and detect any changes that may indicate underdrainage is occurring.
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