8 Boffa Miskell Ltd | Waihi North Project | Terrestrial Ecology Values and Effects of the WUG | 22 June 2022 Coromandel Forest Park Background Coromandel Forest Park (CFP) is administered by DOC and adjoins the north western boundary of the Willows Road Farm. The primary project elements associated with the CFP land will be located underground and comprise a dual decline tunnel, mine excavations and stopes underground drill platforms. Above ground elements within the road reserve (paper road) or conservation estate include up to four vent raises. The existing helicopter pads, accommodation hut and a pump site will continue to be used to service the drilling and mining operation. Vent Raises Vent raises will be constructed from the bottom up using the Alimak method (i.e. constructed from within the tunnel). This method minimises footprint size and level of disturbance on the surface (within CFP). Geotechnical considerations may require additional reinforcement of the vent raise collar, but the surface footprint will be limited to 12 x 12 m. Vent raises will be constructed at different stages of the mine life in response to resource extensions and mining schedules, and vent raises may be converted between intake and return (or vice-versa). Once operating, steam plumes may be visible from return air raise (RAR) discharges under certain climatic conditions (typically during winter and in periods of higher relative humidity). Once mining is complete surface infrastructure will be removed and vent raise areas will rehabilitated. Water Management Incidental, minor quantities of water emanating from the ground and/or from normal tunnelling operations will be drained to sumps within the tunnel. Suitable water will be diverted for recycling underground for mine equipment and surface dust suppression. The balance of water will be pumped to the Waihi processing plant for treatment and discharge. Where significant quantities of water are encountered in tunnelling, the ground in the immediate vicinity will be shotcreted and/or grouted to provide an effective seal to prevent any significant and/or sustained drainage of local groundwater. Current hydrogeological data from the tunnel route is limited, however geology of the area is well understood. It is predicted that the dewatering volume will increase incrementally as the tunnel is developed until completion. Prior to commencement of the first stoping operation, drilling and grouting will be undertaken if required in the upper development drives to ensure no water is lost from surface water bodies when mine dewatering commences. Current data, modelling and expert analysis indicates that the surface water is in contact with the vein system but only at shallow depths and not highly interconnected. Hence such grouting is expected to be highly effective in preventing surface water loss through mining and dewatering. Where necessary, grouting will continue well ahead of mining throughout the mine life. Mining at shallower depths will be or limited and monitored to ensure no risk of surface water drainage. Ongoing work is underway to understand the groundwater system to design appropriate measures to avoid effects on surface water bodies.
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