www.valenza-engineering.com 381_R_04_Rev 0 OGNZL_WUG_Phase1_Conceptual_Mitigation 8 informing likely tunnelling conditions when used in conjunction with surface drilling. Drilling ahead of face advancement is likely to be the only way to fully characterise ground conditions along the alignment and a remedial plan for ground stabilisation, grouting and dewatering will need to be in place to address this. The tunnel is designed to limit the potential groundwater inflow, with incidental seepage anticipated from the intact andesites managed through conventional mine water management, and larger potential inflows from fault zones grouted and sealed ahead of their interception in the tunnel face. 3.2. POTENTIAL GROUNDWATER EFFECTS The assessment of groundwater effects from both the access tunnel development and the WUG underground operations and the mitigation of these through engineered solutions is a prerequisite for the project to proceed. Groundwater interacts with the surface water system both maintaining springs feeding the headwaters of the Wharekirauponga Stream and summer baseflow along its course. Conversely, groundwater recharge is derived seasonally during high-stream flow conditions. Generally, springs are related to the intersection of veins at the surface that brings groundwater from depth. The Waihi Basin aquifer is designated an Aquifer Management Area (AMA) by Waikato Regional Council within the Waikato Regional Plan. The Waihi Basin AMA is sub-divided into the shallow aquifer system (0.5 to 30m depth) and the deep system (>30m). The proposed take for mine dewatering is from the Waihi Basin deep aquifer system. The granting of resource consent for the WUG operation is dependent on an assessment of groundwater and surface water effects. The impact of both access tunnelling, and mine construction and operation on spring flow, stream baseflow and groundwater recharge, will require management and effective avoidance through underground engineered mitigation. Uncontrolled tunnel inflows are likely to be significant where the alignment crosses the regional structures. The most significant of these is the Waihi Fault 1.8km north of the plant portal, containing wide brecciated and shear zones and weak tunnelling conditions (Figure 3-2). Figure 3-2:Tunnel Alignment Showing Hydrogeological Significant Features (Golder, 2021)
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