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 32 Effects on Other Aquifers The flow regime in the shallow groundwater system will be temporarily altered near the excavation during the construction period, with flows locally directed to the excavation. Recharge to the broader groundwater system will be reduced by the volume of dewatered groundwater during construction. The major proportion of groundwater removed during dewatering is expected to come from the deeper aquifer. This results in an approximate reduction in recharge of 0.2% of the Waihi Basin aquifer management level. Effects on Other Groundwater Users There are no groundwater users within the defined envelope of effect during construction dewatering with neighbouring users being > 1 km distance and as such effects on other groundwater users is not expected. Land Discharge Effects Once constructed the TSF will be filled with tailings, and the liner and drainage system will collect much of the leachate. Figure 36 shows the proposed TSF3 structure during the various stages of development. While the drainage system is expected to collect the majority of infiltrating water, some discharge to land is expected through the HDPE liner via pinholes. The maximum predicted seepage through the liner has been assessed as being 95 m3/d and this will enter the groundwater system and eventually reach the Ohinemuri River. Whilst the drains are predicted to capture and remove groundwater recharge from the Waihi Basin, the proportion of combined TSF3 seepage (tailings seepage and embankment rock infiltration) within the groundwater system is expected to increase over the life of the TSF3. Groundwater levels south of the diverted Ruahorehore Stream are predicted to increase up to 0.25 m for the post-closure scenario. As the area is flood-prone and has a shallow water table this increase may be influential for farm drainage and the Ruahorehore Stream. The area is more likely to be impacted during high-rainfall seasons (e.g. winter) and periods of seasonal surface flooding may be lengthened. To avoid extended periods of flooding, drains can be installed to mitigate such effects, as is the current practice in the area. This is expected to be within OGLNZ owned land. The groundwater quality is expected to change as a result of the land discharge with almost all parameter concentrations predicted to increase and will be similar to that observed at the existing TSFs. Given the distance to any neighboring bores this will not results in any direct effects on groundwater users. The ultimate receptor of the land discharge will be the Ohinemuri River. The land discharges have been assessed by GHD with respect to their effects on surface water quality and are stated to be within the RWQC at the compliance point in the River. This is principally due the the high flows in the River having significant dilution potential.
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