Oceana Gold New Zeland Limited Hydrogeology Support for WKP Underground Updated Conceptual Model As shown in Figure 4-2, a sudden water level drop is observed in WKP 01D during May of 2020. This drop is related to a groundwater monitoring event when the piezometer was bailed dry and did not recover (information from OGNZL field data sheet). Notwithstanding the unexplained spike in November of 2020 and smaller rise in July of 2021, since the May 2020 sampling event water levels for most of the year are typically at the base of the borehole suggesting it is dry. There does not appear to be a clear hydraulic connection between WKP 01S and WKP 01D. This is illustrated schematically in Figure 4-3. Figure 4-2 also illustrates that WKP 02D responds more rapidly to rainfall events than other shallow piezometers. This is likely due to its position in the contact zone of the rhyolite flow dome, where water losses have been observed during drilling. This rapid response to rainfall events suggests that the contact zone may be capturing shallow interflow that would normally discharge further downgradient. Figure 4-3 Schematic section showing conceptual shallow groundwater In the WKP-01 S/D pair, water levels in the shallow bore appear to be unconnected to the deeper bore, which is mostly dry. In this area, there may be an unsaturated zone between the shallow aquifer and deeper groundwater. In the WKP-02 S/D pair, there are downward vertical gradients and interpreted continuous saturation. Piezometer WKP-02D responds more strongly to rainfall than other shallow bores and fluctuates over a 10-meter range. This may be due to its position at that contact of the rhyolite flow dome, where water losses have been observed during drilling Suggests that the rhyolite flow dome contact may be capturing shallow interflow that would normally discharge downslope to streams
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