SECTION 5 Groundwater Effects Assessment – WUG Dual Tunnels 30 Table 6 Hydraulic Conductivity Values Geologic Unit Hydraulic Conductivity (m/s) Storativity Whiritoa Andesite 2.5 x 10-8 0.001 Waipupu Andesite 2.5 x 10-8 0.001 Clay Altered Andesite 5.0 x 10-9 0.0001 Silicified Andesite 1.0 x 10-7 0.001 Fault Zones 1.0 x 10-5 0.01 5.2 Conceptual Groundwater Model The conceptual groundwater model for the dual tunnels is essentially no different to that for Willows Farm. The one main difference is that instead of the tunnel running parallel to the catchment flow, the tunnel crosses beneath the Waiharakeke Stream at around 5,200 m distance. At this location the Stream bed is assumed to coincide with a major mapped fault zone and will act as a preferential pathway for groundwater to move through. The key risk to understand is, therefore, how much baseflow loss will occur in the Waiharakeke Stream when the tunnel passes beneath it. A conceptual groundwater model for the Willows Farm to WUG dual tunnel section is shown in Figure 23. 5.3 Groundwater Effects Assessment 5.3.1 Groundwater Inflows Groundwater inflows for the tunnel have been adopted from the groundwater inflow assessment included in Attachment B. This assessment indicates up to 9,200 m3/d groundwater will be taken from the Otahu catchment. This includes the 4 vent shafts during construction. This volume of water does not consider mine development dewatering volumes as these are included in a separate report by GWS on the groundwater effects at WKP. 5.3.2 Groundwater Availability The dual tunnel section is not within any specific aquifer management area identified by the Waikato Regional Council. For the purpose of this assessment, we have assumed the take to be from the Otahu catchment and an assessment of groundwater availability has been determined as shown in Table 7. This water will be diverted to the treatment plant in Waihi and then diverted to the Ohinemuri River. Table 7 Otahu Catchment Groundwater Availability Deep Aquifer Recharge (10% Rainfall) 15,407,000 m3/year a Availability (35% Recharge) 5,392,450 m3/year Existing Allocated 0 m3/year S14 Takes (10%) 539,245 m3/year b This Proposal (9,200 m3/d x 365 days) 3,358,000 m3/year Allocation Remaining 1,495,205 m3/year a - Deep non-coastal aquifer b - Volume for tunnels only. Excludes exploration or mine development inflows
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