GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 118 Clean water to the Ruahorehore Stream to maintain stream flows. The amount of water taken from this groundwater and surface water catchment is there considered to be a net zero take. – Reduction in recharge to the shallow aquifer and Ruahorehore Stream flows: The lowering of shallow groundwater levels during dewatering are expected to influence the flow within the Ruahorehore Stream. As above, any reduction in stream flow is expected to be mitigated by clean water diversion from the excavation back into the stream. The effect of dewatering on the Ruahorehore Stream flows are expected to be monitored, manageable and thus minimal. – Soil moisture: Whilst there may be some localised changes in soil moisture in close proximity to areas of earthworks and dewatering, no impacts are expected beyond the immediate vicinity of the works during the temporary nature of the works. Intermittent wetting by rainfall is considered to provide the greatest influence on soil moisture levels across the WNP area. – Effects to groundwater quality: Abstraction of groundwater during construction dewatering is not expected to adversely impact the aquifer water quality. The depth and volume of the take is not considered sufficient to induce saline intrusion from deep basement rock or the coast. – Effects to Ohinemuri River flows: 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. – Effects to private water resources: Groundwater users are discussed in Section 5.3.6 and are shown on Figure 5.17, which also presents the 610 m TSF3 dewatering ZOI (from Figure 5.14). One groundwater user is registered within the ZOI (AUTH131303), but the bore for this take (ID 72_8695) is located outside of the ZOI. Therefore, no significant effects are reported to water users resulting from groundwater level drawdowns. Reductions in stream flow are not expected to impact the downstream surface water user (AUTH120591), based on the proposed diversion of groundwater to the stream. They are also located downstream of the Waione confluence, which contributes significantly higher flows than might be reduced through the TSF3 part of the catchment.
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