GHD | Oceana Gold (New Zealand) Ltd | 12552081 | Waihi North 76 . The presence of the higher transmissivity ignimbrite and alluvium paleo-channel along a similar alignment to the stream is expected to provide a preferential groundwater flow pathway for shallow groundwater from the NRS site towards the Ohinemuri River (demonstrated in piezometric groundwater contours in Appendix C). The deep aquifer within the andesite in the vicinity of the NRS is inferred to flow to the west and is sufficiently deep to be hydraulically separate from the proposed NRS facility. The shallow groundwater system is comprised of permeable alluvium, as well as lower permeability ignimbrite and dacite units. Permeability generally decreases with depth (Table 4.1) as the degree of weathering reduces and flow relies more on secondary porosity (fracturing) rather than primary porosity. Table 4.1 Permeability of NRS geological units Groundwater System Geological Unit Geomean Permeability (m/s) Shallow (water table) Alluvium >1 x 10-4 Ignimbrite (completely weathered) 3.5 x 10-6 Dacite (completely weathered) 1.0 x 10-6 Deeper (up to 25 m) Ignimbrite (highly weathered) 1.1 x 10-6 Dacite (moderately – highly weathered) 8.5 x 10-7
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