EGL Ref: 9049 23 June 2022 Page 5 File: WAI-985-000-REP-LC-0050-Rev0.docx This report shall only be read in its entirety. units around the Waihi township area are generally less prone to ground settlement effects due to their greater depth, lower permeability, and lower compressibility. Martha Open Pit intersects both the younger volcanics and older andesites. The underground mines are within the andesites. Dewatering caused by mining of the deeper andesite units causes settlement at the surface, however at Trio and Correnso Underground, due to their depth, tilt has generally not been an issue. Favona Underground is in an upper unit of the andesite with an overlay of hydrothermal breccia and tuff, and a thinner thickness of younger volcanics over the andesite. This area has experienced higher tilt, however there are no structures in this area for which the effects are consequential. 2.3. Historic mining operations Historical mining in Waihi occurred from 1880 to the 1950s (Ref. 21). This included deep underground workings around the main gold bearing veins. The workings and dewatered reached approximately 660 m below the Waihi township. This would have caused settlement and consolidation of the ground. Settlement from historical mining was not surveyed. After historical mining, partial rebound of the ground surface would have occurred. As a result of the historical consolidation of the ground in the areas of historical dewatering, settlement effects are reduced compared to areas of primary or first dewatering of the ground. 2.4. Modern mining operations In 1988 open pit mining of Martha Hill began to form Martha Open Pit (Figure 2). This involved large scale excavation of both overburden soil and rock, and ore. Martha Hill was an area of extensive historic underground mining and some surface mining. Re-dewatering of these areas has caused ground settlement, albeit of a lesser magnitude than historical mining, due to pre-consolidation of the soil and rock. In late 2004 construction began on the decline (access tunnel) for the Favona Underground (Figure 2), with the extraction of ore in 2006 (Ref. 23). Favona Underground is 1.5 km southeast of Martha Open Pit. Before developing the Favona Underground the area already had some settlement from Martha Open Pit dewatering (Ref. 9). Favona Underground was extended to the south to include the Moonlight section of the vein system just to the west of the Processing Plant. Ore production from Favona Underground including the Moonlight development (Figure 2) was completed in 2014 (Ref. 22). Concurrently Trio Underground was developed to the west 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 and was close to complete in 2021. Correnso Underground was the first modern underground undertaken directly under private residential and commercial property not owned by the mining company. Martha Underground development and underground bores were drilled for dewatering, beginning in July 2020. Martha Underground is currently being developed.
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