GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 55 . 3.5.2 Groundwater flow to receiving environment During GOP excavation and dewatering, loss of recharge and reduction in shallow groundwater levels is predicted to reduce shallow groundwater flow to surface water to a small degree, with the predicted changes summarised in Table 3.10. No changes in shallow groundwater flow to the north, towards the Ohinemuri tributary TB5, are predicted to result from GOP excavation. This is because the existing groundwater catchment area and groundwater gradients within the catchment are not predicted to be impacted. Table 3.10 Predicted groundwater discharge to surface water during GOP excavation Surface water body Estimated groundwater discharge to surface water body (m3/day) Percentage change in groundwater discharge Percentage change in groundwater catchment area Current conditions GOP excavation scenario Gladstone wetland / Ohinemuri tributary (TB4) 1.0 0.7 -30% -20% Ohinemuri River east of Gladstone (OH3) 50 50 <-1% -10% Ohinemuri River west of Gladstone (OH6) 215 160 -30% -20% Notes: - Considering model uncertainty, results have been rounded. 3.5.3 Surface water catchments The reduction in the surface water catchment areas due to GOP excavation is predicted to reduce runoff and interflow, and hence peak flow in the tributaries. The predicted change in catchment areas are presented in Table 3.11. Table 3.11 Predicted change in surface water catchment areas during GOP excavation Surface water catchment Percentage change in catchment area Gladstone Wetland / Ohinemuri Tributary (TB4) -26% Ohinemuri Tributary (TB5) -16% Ohinemuri River west of Gladstone (OH6)1 -20% Ohinemuri River east of Gladstone (OH3)1 -20% 1. Constrained to the area between the Gladstone Pit and Ohinemuri River 3.6 Gladstone TSF analysis results The below sections provide summarised assessment results, with additional detail provided in Appendix G. 3.6.1 Groundwater levels and flow The predicted groundwater drawdown from current conditions at the edge of the pit after development of the TSF and the drawdown ZOI are presented in Table 3.12. The predicted groundwater table with distance from the pit is presented for all scenarios in Appendix G. Predicted groundwater levels and groundwater flow paths for each TSF scenario are also represented in the cross sections in Figure 3.16, Figure 3.17 and Figure 3.18.
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