SECTION 3 Groundwater Effects Assessment – WUG Access Tunnel 12 At some point along the tunnel decline, fully saturated conditions will be encountered. As the tunnel is driven, groundwater will be intercepted and the adjacent rockmass will be depressurised. Dewatering to the ground surface will not take place due to the relatively low permeability of the andesite and the perched shallow groundwater system which has substantially greater storage and rainfall recharge. 3.4 Groundwater Effects Assessment 3.4.1 Groundwater Inflows Groundwater inflows for the tunnel have been adopted from the groundwater inflow assessment included in Attachment B. This assessment indicates up to 3,000 m3/d groundwater will be taken from the Waihi Basin catchment during construction and returned to that catchment after treatment. 3.4.2 Groundwater Availability The WUG access tunnel is located within the Waihi Basin aquifer management area as identified by the Waikato Regional Council (WRC, 2012). This catchment is further subdivided into the Waihi Basin shallow aquifer system (0.5 to 30 m depth) and the Waihi Basin deep aquifer system (>30 m depth), however the resources are managed as one. The availability of groundwater for the Waihi Basin is shown in Table 2. Table 2 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 Total WNP Takes 1,616,950 m3/year Remaining 228,050 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 On the basis of this assessment, there is sufficient groundwater available for the proposed take. 3.4.3 Potential for Effects on Springs and Streams Groundwater modelling has been undertaken to assess the effects of the tunnel on the near surface environment. The modelling has indicated that once the tunnel is 20 to 30 m below the ground surface, depressurisation effects are limited to the rockmass surrounding the tunnel with no connection with the surface or shallow groundwater system expected. Given that the tunnel decline is already dewatered to a depth of approximately 70 m below the ground surface, and the tunnel will continue to be driven at a depth greater than that, no
RkJQdWJsaXNoZXIy MjE2NDg3