EGL Ref: 9049 23 June 2022 Page vii File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. • Avoid intercepting historical workings with the tunnel wherever practicable. • Drilling ahead of the tunnelling operation, to inspect for geological structures or areas of ground that may make notable water inflows into the tunnel. • Mitigation of sustained groundwater inflows through the use of grouting methods. Dewatering and ground settlement monitoring recommendations Monitoring of groundwater levels and ground settlements is required to check settlements are within estimates and there are no unforeseen effects. The dewatering and settlement monitoring plan will be updated for the Waihi North Project. Recommendations in regard to dewatering and ground settlement monitoring are summarised below: • Continued monitoring of dewatering and settlement as required by the expired Mining Licence and resource consent 124860. • The settlement monitoring zones and settlement trigger limits previously proposed for Project Martha are adjusted over the Favona Underground and locally around Gladstone Open Pit and Wharekirauponga Access Tunnel alignment for the Waihi North Project. • The dewatering and settlement monitoring plan needs to be updated for the Waihi North Project. • Groundwater monitoring piezometers provide the best early warning of potential adverse ground settlement effects such as tilt. This was evident in the situation which occurred in Gladstone Road related to borehole CDG008 as described in Section 5.3.3. EGL recommends that additional piezometers are installed along with the new settlement markers in areas where there are residential dwellings or other structures not owned by OGNZL. • Recommended additional settlement monitoring markers and piezometers to measure potential settlement effects are summarised below and in Figure 66 to Figure 69: o Potential dewatering of the Gladstone vein south of GOP ▪ Heath Road – Additional settlement points (Figure 67) ▪ Clarke Street – Additional settlement points (Figure 67) o Additional settlement monitoring points around Gladstone Hill to provide an understanding of the settlement effects close to the pit. o Potential dewatering of the ignimbrite between the Wharekirauponga Access Tunnel decline and Boyd Road and Barry Road. ▪ Boyd Road – Additional settlement points (Figure 68)
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