EGL Ref: 9049 23 June 2022 Page 17 File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. higher elevations the water table is tens of meters below ground level. At lower elevations the depth to groundwater is between 1 to 5 m. Perching of groundwater is noted to occur in the shallow materials overlying the volcanic rockmass. The portal cut will be at higher elevations and is expected to have only local drawdown in the rock which it is cut. Insitu permeability testing was undertaken as part of the investigations by GHD and Golder (Ref. 38). GWS (Ref. 36) summarised that the andesite, which is the main geological unit the access tunnel is to be driven through, has a permeability of approximately 3.0 x 10-8 m/s and is similar to that adopted elsewhere in Waihi. GWS (Ref. 36) noted given the rockmass dewatered by the tunnel is of low permeability, any associated dewatering effects are expected to be limited. GWS (Ref. 36) assessed the potential groundwater drawdown profile above the tunnel. The estimated drawdown was 3.5 m above the tunnel with no discernible drawdown 600 m from the tunnel. They noted most of this effect would be within Willows Road Farm. The closest dwellings not owned by OGNZL are on Willows Road and Highland Road. Both are over 600 m from the decline access tunnel. The Willows Access Tunnel passes beneath the proposed Willows Rock Stack. 4.5.4. Wharekirauponga Dual Tunnel The Wharekirauponga Dual Tunnel fromWillows Access Tunnel to the WUG site is at depth (approximately 130m to 420m) within andesite rock. GWS (Ref. 36) note that any drainage effects will be localised to around the tunnel, and they will not manifest in the near surface, due to the relative depth of the tunnel. They note no intrusive groundwater investigations along the tunnel alignment have been undertaken and this is considered justified based on the geology being similar to that at Waihi and the proposed mitigating tunnelling methodology that will ensure drainage effects are managed. This includes pre-grouting of any high inflow zones and allowing only rockmass drainage to occur. Geotechnical boreholes will be drilled ahead of the tunnel in advance to give prior warning of geotechnical and groundwater conditions. 4.5.5. WUG – Mine drives, shafts and stopes The host rock at WUG is rhyolite flows and pyroclastic deposits. The rhyolite overlies andesite. Permeabilities within the rhyolites are currently understood to be higher than the andesites (Ref. 41), however more detailed investigation and modelling is ongoing. The current assumption is that the host rhyolites will be dewatered to the full depth of the WUG mine and shallow surficial groundwater systems will be protected with measures to avoid effects at the surface (restricting mining within a certain distance of the ground surface or geological units, grouting to restrict seepage).
RkJQdWJsaXNoZXIy MjE2NDg3