GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 113 Figure 5.14 Predicted groundwater level drawdown beneath TSF1A (SEEP/W Cross-Section 2 and Theis, 1935) 5.5.2 Tailings discharge Leakage of tailings porewater is expected to occur as seepage through HDPE liner defects and through the Zone A soil liner below the HDPE liner and on the upper sections of the embankments. Seepage rates through the HDPE liner has been suggested by EGL (2019b) based on work carried out by others (e.g. Kerry Rowe) to be between 42 to 170 L/ha/d due to defects or holes within the liner. The upper limit has been conservatively adopted for this analysis. Downward gradients are predicted to dominate through the Zone A liner during all stages of TSF3 life. A portion of tailings porewater is therefore expected to seep to ground beneath the proposed TSF3, and residual soluble components of the tailings porewater may migrate with groundwater flow. Groundwater impacted by tailings porewater, at the northern extent of TSF3, is predicted to discharge to the deeper aquifer (Figure 5.15). This is indicated by flow paths within the SEEP/W model and the conceptual understanding provided in 5.3.5. During initial construction stages, the tailings discharge is predicted to be captured by the TSF3 drainage system (Figure 5.15). As TSF construction progresses through to full embankment (1,155 m RL crest height), the tailings will be emplaced above the top elevation of the HDPE liner (1,135 m RL) to approximately 2 m below the crest level. For conservatism, the tailings are modelled at the full crest heigh for each scenario. Some of the tailings
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