32 Tonkin & Taylor Ltd Hazardous Substances Technical Assessment – Waihi North Project - Storage and use of hazardous substances at Willows Road site and the Wharekirauponga Underground Mine Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.1000 vRev0 Vulnerable facility definition (HSW-HS 2017) Conservation (Indigenous Forest) zone Rural zone Buildings of 4 storeys or more with more than 50% of the wall area glazed: Not permitted – height restriction of 6 m (permitted) and 8 m (RD) Not permitted - Only dwellings and buildings accessory to farming permitted. Aa hospital care institution, residential disability care institution, or rest home (as defined in section 58(4) of the Health and Disability Services (Safety) Act 2001), early childhood education and care centre (as defined in section 310 of the Education Act 1989), or school (as established under section 146 of the Education Act 1989): Not permitted. Not permitted - Only dwellings and buildings accessory to farming permitted. Public buildings or structures of historic value: None existing. None existing. Major transport and traffic terminals such as railway stations and airports handling more than 1,800 people in 24 hours: Not permitted. Not permitted. Major public utilities whose service could be disrupted by a blast of 5 kPa: None existing. None existing. Any similar facilities. None existing. None existing. 5.3 Underground explosives storage facility offsets The proposed underground storage facility will consist of seven separate purpose-built chambers, six of which are dedicated to H.E. and one for the I.E. as shown inFigure 4.2. In the event of an unintended detonation, the overpressure would propagate through the mine space and be expelled at the surface vents. In respect to the required controlled zones under r9.27, each surface vent identified in Section 3.2 has been considered. These areas are where the blast overpressure will be vented and where impacts on off-site people or public could be anticipated. The location assessment report by GSS (Appendix B) for the underground storage facility details the minimum offset distances summarised inTable 5.3below. The overpressure value calculated assumes that an entire chamber detonates at once and that the chamber is at maximum capacity, and will therefore be conservatively high. Additionally, the volume of the underground mine used for calculation of the blast pressure has considered the travel path volume to the surface vents only, which will underestimate the total mine volume by excluding some of the available mine space and therefore conservatively increase the predicted pressure at the surface vents. The storage facility has been designed with separation distances between the different chambers, such that the risk of explosion propagation between explosive components is mitigated (See Section 4.2.2.2). Therefore, the scenario considered for the calculation of controlled zones at the surface vents is a detonation at the largest of the chambers, where a maximum of 1,000 kg of Class 1 explosives are proposed to be stored. Full calculation of the blast overpressure can be found in Appendix B. Table 5.3 below sets out the calculated offset distances (to the nearest metre) for each surface connection site and compares them with the requirements of r9.27.
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