EGL Ref: 9049 23 June 2022 Page 21 File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. 5.3.3. Correnso Area Two tilt calculations greater than 1:1,000 in the Correnso South area were identified during the May 2020 survey and remain in the November 2021 survey. The tilts are between marks 23C/2.25 and 23C/BANK1 (Figure 49). Both tilts are due to a sharp increase in settlement of mark 23C in the May 2020 survey. The mark is noted by the surveyor as being near a watercourse. The mark may have been influenced by improved drainage nearby or may have been disturbed. The rate of settlement recorded at 23C in subsequent survey events has been similar to nearby marks, indicating that increased settlement at this point, if it were occurring, is not ongoing. 5.3.4. Favona Underground Mine Settlements above the Favona Underground have been greater than originally predicted and tilts have exceeded 1 in 1,000 at five locations. The locations are directly above the underground workings and vein system on farmland owned by OGNZL. No buildings have been affected. The closest dwelling is on OGNZL owned land and is within 30 m of the recorded tilts. The nearest non-OGNZL dwelling is approximately 120 m from any tilts greater than 1:1,000. The original settlement estimates only considered settlements in the younger volcanic deposits (Ref. 3). If allowance is made for settlement in the geologic units that underlie the younger volcanic deposits (i.e. hydrothermal tuff, hydrothermal breccia, andesite and dacite) then the predicted settlements are closer to the measured settlements. 6.0 ASSESSMENT OF GROUND SETTLEMENT EFFECTS – WAIHI NORTH PROJECT 6.1. General Prior to commencement of mining in 1987 and subsequently again in 1997 (Ref. 2), theoretical predictions of the future ground settlements due to mine dewatering were made. Since then, throughout the life of the mine, ground settlements have been measured at six-monthly intervals at hundreds of locations in Waihi township. The large number of settlement observations, spanning some 32 years, provides a reliable database for estimating likely future settlements associated with further dewatering. The monitoring undertaken at Waihi makes it one of the best monitored sites in New Zealand and provides an excellent database for predicting future settlements. Assessment of ground settlement is based on both review of past settlement trends and theoretical calculations (where relevant). Past assessment for Project Martha (Ref. 7) has set the ongoing settlement trigger levels for the seven settlement monitoring zones (refer to Table 1 and Figure 51). Settlement trigger levels are set to drive review of settlements which may be higher than expected, to check that there are no adverse effects occurring. Settlement predictions were based on the observed settlements trends extended for the potential dewatering effects of Project Martha. This approach follows two key steps:
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