SECTION 5 Conclusions & Recommendations C:\D Data\GWS C Drive\GWS\Client Files\1344 OGL - WKP\4 Deliverables\WKP Final Draft Report\June Report\WAI-985-000-REP-LC-0030. Final_Rev_0.docx 42 EG vein, could potentially be affected by dewatering of that vein system. The Edmonds Stream headwater spring discharges are small and at a catchment scale, losses would likely be immeasurable. Further quantification of this is being undertaken by Flosolutions and mitigation is being designed by Valenza Engineering. Aside from the stated connections to surface waters, this assessment has indicated that dewatering of the vein system to allow mining is not expected to result in any other effects that would result in an adverse environmental outcome. The effects from dewatering of the deep groundwater system on the shallow groundwater system can be avoided by mine design and proximity of mining to the surface. Where localised connections do exist, these can be mitigated though grouting in advance of or during the mining process. 5.2 Recommendations for Monitoring In order to verify the predictions made herein to assess whether mitigation of effects is required, it is recommended that ongoing monitoring of surface and groundwater takes place prior to and during dewatering. It is recommended that surface water flows are monitored at permanent gauging locations upstream and downstream of the mineralised zones. The purpose of the monitoring is to detect any potential baseflow losses through the bottom of the stream. Further details related to the surface water monitoring is included in the GHD report (April, 2022). In addition, it is recommended that multi-level standpipe piezometers be installed at critical locations adjacent to the stream for ongoing monitoring. The purpose of the piezometers is to assess the vertical gradients and detect any changes that may indicate underdrainage is occurring. As well as monitoring adjacent to the Streams, piezometers could also be constructed in the EG vein system to provide an early indication of depressurisation effects. Such a monitoring network would allow an early detection and compliance system similar to that applied in the Waihi operations. The combined surface water and groundwater monitoring will provide a sufficiently robust system that can detect changes in groundwater-surface water interaction and inform mitigation actions if required. Details of the proposed baseline and operation monitoring of groundwater levels is included in the Valenza Engineering report (May 2022) report.
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