SECTION 8 Tailing Storage Facility 3 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 31 Figure 35 TSF3 Conceptual Hydrogeologic Model (From GHD 2022) 8.4 Summary of Effects Groundwater Inflows For the initial phase of construction dewatering will be required for foundation preparation. The assessment undertaken has indicated between 1,970 - 16,300 m3/d of groundwater could be generated from the excavation. The range of inflow volumes is a function of the cross section modelled and represents an upper and lower bound. Actual groundwater inflows are expected to be on the lower end of this range and in the order of 2,500 m3/d and is temporary. Drawdown Extent During the initial excavation phase there will be a lowering of groundwater levels to a maximum depth of some 15 m and the zone of influence from the dewatering will extend up to 610 m. Effects on Surface Waters The Ruahorehore Stream will be diverted to approximately 40 m south of its current location at the toe of the TSF3 embankment. Without this diversion the Ruahorehore Stream would be significantly adversely affected by TSF3 construction dewatering. Rates of stream depletion have not been quantified, as any effects to the Ruahorehore Stream are expected to be mitigated by diverting clean abstracted groundwater during the dewatering. A loss of deeper groundwater recharge is expected to occur. The estimated reduction in flow to the Ohinemuri River median flow, if unmitigated, is estimated to be 0.4%. Although minor, this influence on river flow is expected to be mitigated by clean water diversion from the TSF3 catchment to the stream and discharge to the river following treatment at the WTP. This is anticipated to result in a net neutral effect to the Ohinemuri River flow.
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