EGL Ref: 9049 23 June 2022 Page 11 File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. 4.2. Martha Open Pit, Favona, Trio and Correnso Underground Dewatering 19892021 Dewatering of the Martha Open Pit occurred progressively. Dewatering was achieved by installing pumps into the main shafts associated with historical underground mining beneath the pit. A record of the mine dewatering level over the life of the mine is shown in Figure 4. Reference reduced levels (RL) for key mine and geological features are also shown on Figure 4. Monitoring of dewatering levels was undertaken from shafts in the bottom of Martha Open Pit until 4 May 2015, when the slip occurred on the North Wall of the pit. Dewatering levels since 2015 are based on pumping levels in Correnso Underground and underground bores for MUG development. The dewatering has been carried out at different rates during the period and sometimes the water level has been held near constant (refer to Figure 4). Records at Martha Open Pit begin with the groundwater at approximately RL1110m in 1989. The average rate of drawdown in the pit from 1989 to 1998 was about 16 m per year. Between 1998 and 2000 the groundwater level at the pit was at approximately RL970m. In 2000 and 2001 it was drawn down 30 m to RL940m. Between 2001 and 2003 the groundwater level at the pit was maintained between RL940m - RL960m. It was then lowered progressively 70m from RL960m to about RL890m from about May 2003 to December 2006, at an average rate of approximately 20 m per year. Groundwater levels beneath Martha Open Pit were held close to RL 890m until June 2009. Concurrently from 2004 the Favona Decline was developed, with the decline reaching near full depth early 2008 (see indicative depth of decline construction on Figure 4). The development of the decline is notable as the Favona vein system was understood to not be hydraulically connected to the Martha vein system and had not been dewatered historically. The decline for Favona was developed from the existing Favona Portal in Gladstone Hill (see Figure 3). Martha Open Pit was dewatered a further 15 m to RL875m between June 2009 and December 2010 at an average rate of drawdown of approximately 10 m per year. The rate of dewatering was then increased to about 70 m per year from December 2010 to November 2011, with the water level was reduced from RL875m to RL807. It was slowly lowered to about RL790m from November 2011 to May 2015. Concurrently Trio Underground was developed under Union Hill from 2010 (Ref. 23), with ore production beginning in 2012 and finishing in 2014 (Ref. 22). Correnso Underground development began in 2014. This was the first modern underground mine in Waihi undertaken under private residential and commercial property not owned by the mining company. In 2015 there was the slip on the north wall of Martha Open Pit which prevented access to the dewatering pumps which were located in the pit in the old mine shafts. After this the dewatering was undertaken from the Correnso Underground. Slow dewatering continued to approximately November 2017, after which the dewatering rate was increased and the level was lowered at a rate of approximately 55 m per year to RL705m by Jan 2019. The level of the sump in Correnso (Gladstone Sump) remains at RL705m. Correnso Underground was close to complete in 2021 with the majority of the stopes mined and backfilled. Dewatering for Martha Underground commenced in July 2020 from two underground bores drilled below the RL800m exploration drives
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