SECTION 3 Groundwater Effects Assessment – WUG Access Tunnel 8 3.2.2 Hydrology The WUG access tunnel is within the Waihi Basin surface water catchment which drains to the west. The main channel is the Ohinemuri River and this is east of the proposed tunnel alignment. The tunnel does not pass beneath the Ohinemuri River but will be driven below tributaries to the river. 3.2.3 Geology The geology of the WUG access tunnel is described in detail (Golder, Sept 2021) and shown in cross section in Figure 5. In summary, the tunnel will pass through Waipupu Formation Andesite (aw) which consists of andesitic flows, breccias, tuffs some of which is hydrothermally altered. The tunnel will then pass through the younger Whitiroa Andesite (ah), being andesitic flows, breccia and tuffs, before returning back into Waipupu Formation Andesite. The younger andesite is present in the mid-section of the alignment due to being in a down thrown block that is bounded by regional scale faults. It is expected that there will be fracture zones associated with these faults and that ground conditions will be weaker than the general andesite rockmass. These zones are expected to be permeable and will allow some groundwater inflow prior to grout sealing. Figure 5 WUG Access Tunnel Profile (Modified after Golder, Sept 2021) 3.2.4 Hydrogeology At the location of the WUG access tunnel the groundwater system consists of surficial deposits of alluvium and younger volcanic materials that host a shallow water table as shown in Figure 6. These deposits have formed in a paleo channel on the surface of the underlying andesite rocks. Groundwater flow is in a south east direction driven from heads in the Coromandel Ranges. The proposed WUG access tunnel does not intercept these materials.
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