88 14.4.7 Water Management Rock stack runoff will be collected in the collection pond (situated at the base of the rock stack) before being pumped via a dedicated pipeline to the existing OceanaGold WTP. GHD (2022A) notes that it is assumed that WUG water is piped and pumped through the tunnels directly to the WTP without surfacing at Willows Road Farm during peak development. We also note that the same report assumes that the groundwater inflow is constant and is the dominant water source requiring treatment. The flows presented in GHD (2022A) assume decreasing collection pond water requiring treatment in line with the reduced footprint of the WRS but no reduction in groundwater inflow due to backfilling. Therefore, no water impacts are expected based on the assumed infrastructure for the WUG. WUG groundwater will be pumped and piped directly to the WTP and collected runoff and seepage from the rock stack will undergo similar transport via storage in the collection pond. The predicted impact is detailed in GHD (2022) and is conservatively based on the maximum constructed height and extent of the WRS, no groundwater dilution or attenuation. 14.5 Summary of Effects Assessment on Freshwater Ecological Values at Willows Farm The level of effect on freshwater ecological values from the proposed activities range from low to high (Table 27). Our assessment of the magnitude of the different effects assumes that the effects will be subject to the design parameters provided for and the mitigations we have recommended (i.e., design of tributaries, fish passage through culverts, etc). Direct impacts on the unnamed tributary 2 of Mataura Stream will be remedied through conducting fish relocation, and residual effects of 390 m of stream reclamation will be offset through enhancement of 1,150 m of existing stream habitat at tributary 3. An overview of the ecological values, the magnitudes of the different effects and the assessed level of effect is provided in Table 28. The EIANZ guidance is that low and very low effects should not normally be of concern, but that these effects should still be minimised through appropriate design and management. We provide recommendations to manage effects and implement the proposed designs within the next section. Table 27: Overview of the level of adverse effects on the freshwater ecological values at Willow Road Farm. Feature Ecological value Effect Magnitude of effect Level of effect with management Mataura Stream High Earthworks and sediment discharge Low Low High Contaminant water management Low Low Tributary 2 Low Reclamation of 390 m of stream habitat High Very low Instream works Low Very low Reduced aquatic connectivity Low Very low
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