EGL Ref: 9049 23 June 2022 Page 26 File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. around 2017 and has slowed around 2020. This indicates some form of hydraulic link to dewatering of the Martha vein system. EGL recommends that the area expected to exceed the Zone 5 trigger limits is redefined as Zone 6. Proposed adjustments are shown on Figure 66 and Figure 69. In this area, tilt greater than 1:1,000 occurs. No private structures are affected. This tilt is currently reviewed at six-month intervals. Continuing this review is prudent to make sure that the tilts do not extend to the privately owned dwellings in Boyd and Barry Road, with continued dewatering for Martha Underground and with the development of the Wharekirauponga Access Tunnel proposed. Boyd Road and Barry Road are in settlement monitoring Zone 4. The settlement trigger level is 160 mm. Settlements in the area, away from the effects of Favona Underground, are typically 90 to 110 mm. The settlements in November are 56 to 69 % of the trigger level, with 73 % of the currently proposed drawdown in the Waihi vein systems undertaken. Keeping the Zone 4 settlement trigger level in this area is recommended. Additional settlement monitoring points are recommended along Boyd Road to provide monitoring of any progression of tilts away from the Favona Underground. 6.1.4. Wharekirauponga Access Tunnel east of Waihi East Calculations of potential seepage and settlement have been undertaken for a representative profile east of the Waihi Township where the Wharekirauponga Access Tunnel will be developed. This area covers settlement Zones 1, 3, and 4. The assessment was undertaken to estimate the potential additional settlement and tilt that could be expected. The modelling provided estimates of settlements due to dewatering to RL940m, approximately the expected low point of the tunnel. In the model the tunnel is in the fresh andesite with a 50 m thick weathered andesite directly overtop which provides notable hydraulic separation from the younger volcanics. Two different situations were considered: 1. With the tunnel causing local depressurisation around the tunnel in the andesite rock mass 2. With the tunnel causing local depressurisation in multiple veins The setup of these models is similar to the previous modelling done for Waihi East as part of Project Martha, however, they assume that there is no previous depressurisation of groundwater in this area. Settlement monitoring indicates there is some depressurisation in this area already, however it is not known to what extent. For the same conditions, the modelled groundwater depressurisation is likely to be greater than actual, and therefore the modelled settlements may be higher than actual, for this reason. The average modelled settlements for the depressurisation around the tunnel in the general andesite rockmass is negligible at 8 mm.
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