SECTION 4 Groundwater Effects Assessment – Willows Farm Access Tunnel 23 4.3 Groundwater Effects Assessment 4.3.1 Groundwater Inflows Groundwater inflows for the Willows Farm access tunnel have been adopted from the groundwater inflow assessment included in Attachment B. This assessment indicates that the decline would generate in the order of 500 m3/d groundwater from the rockmass during construction. 4.3.2 Groundwater Availability The Willows Farm access tunnel sits just outside of the Waihi Basin aquifer management area as identified by the Waikato Regional Council (WRC, 2012), but for the purpose of this assessment has been included in the availability calculations to remain conservative. The availability of groundwater has been determined as shown in Table 4. Table 4 Waihi Basin Groundwater Availability Management Limit a 6,000,000 m3/year Existing Allocated 4,155,000 m3/year Available b 1,845,000 m3/year Other WNP Takes (GOP, TSF3) c 521,950 m3/year WUG Access Tunnel d 1,095,000 m3/year Willows Farm Decline e 182,500 m3/year Total WNP Takes 1,799,450 m3/year Remaining 45,550 m3/year a - Combined shallow and deep limits b – WRC advised 23/11/2021 c – Based on GOP take of 1,100 m3/d and TSF3 take of 330 m3/d for 365 days d- based on 3,000 m3/d for 365 days e- based on 500 m3/d for 365 days On the basis of this assessment, there is sufficient groundwater available for the proposed take. 4.3.3 Potential for Effects on Springs and Streams The potential for effects of the tunnel construction on springs and stream flow have been undertaken using numerical modelling in SEEP/W (R2 2019). This entailed constructing a model section that replicates the hydrogeologic conditions perpendicular to the access tunnel across Willows Farm assuming three scenarios; • Assuming high permeability conditions replicating preferential flow along a fracture zone (K = 1 x 10-5 m/s) • Assuming typical rockmass being fresh andesite (K = 2.5 x 10-8 m/s) • Assuming typical rockmass being fresh weathered tuff (K = 1.0 x 10-7 m/s)
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