www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 7 Figure 3-1:WUG Proposed Tunnel Alignment The CSM was developed based on limited intrusive investigation and is intended to support further studies at a high level, including groundwater modelling and both physical and chemical surface water interaction. Significant faults and lineaments identified from surface mapping likely to control groundwater inflows to the tunnel were included together with lithological controls resulting from hydrothermal alteration (e.g., clay mineral development and silicification) and formation changes (e.g., andesite and rhyolitic ignimbrite). The tunnel alignment in relation to published geological mapping is provided in Figure 3 of Appendix A. The tunnel passes through Waipupu Formation Andesite (aw/Mci) consisting of andesitic flows, breccias, and tuffs some of which are hydrothermally altered. The tunnel then passes through the down-thrown Waihi Fault block of the younger Whitiroa Andesite (ah/Mco), consisting of andesitic flows, breccia and tuffs, before turning into Waipupu Formation Andesite. The tunnel crosses the regional Waihi Fault approximately 1.8km north of the plant portal, where ground conditions are expected to deteriorate in the presence of wide (10s to 100s of metres) brecciated zones and locally developed sheared clay gouge zones. Ignimbrites are likely to present locally poor ground conditions with low strength material and potential for high groundwater inflows. Rapid changes in tunnel face conditions can be expected with variable strength materials and groundwater inflow. The understanding of anticipated tunnelling conditions could be improved through a surface drilling campaign accompanied by geomechanical and hydrogeological testing and sampling. The tunnel zone around the Waihi Fault should be targeted. Geophysical investigations provide a non-invasive method for
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