45 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 The qualitative risk analysis serves as a screening assessment to identify events where the residual risk may be significant and require further quantitative assessment. Where risks are identified that can be managed and are acceptable in terms of a qualitative assessment, no further evaluation is considered necessary. The assessment has been based on information from OGNZL from their own and similar mining operations elsewhere, and professional judgement. There is one residual risk associated with the proposed activities as identified inAppendix K Table 4 that was assessed as moderate as follows: Moderate residual risk to the ecosystems from a spill of diesel, through a spill during tank refilling or equipment refuelling and low risk from a tank leak, which is managed through physical controls including tank bunding, automatic shut-offs on fuel nozzles, refuelling pad drainage to API separators, maintenance programmes, and management provisions including emergency response planning, spill kits and staff training. All other residual risks were assessed as low, including: Low residual risk of fire impacting offsite locations at the oxygen or acetylene storage at the workshop in the SFA, or for the diesel and ANE storage areas at either the SFA or in the WUG. The likelihood of a fire at these storage areas is minimised through prevention measures such as access restrictions, exclusion of ignition sources and segregation of incompatible or reactive substances. The consequence of a fire is minimised by the separation distances to buildings, combustibles and the site boundary at the surface, as well as emergency management measures including fire-fighting facilities and staff emergency response training. Low residual risk to ecosystems from a spill of packaged goods such as maintenance oils or gasser during unloading to site. This is managed through physical controls including the sealed unloading areas to prevent discharges to the environment and tertiary containment provided by the settling ponds. Small spills are primarily managed through staff training and emergency response planning including spill kits at unloading areas. Low residual risk to occupants of off-site properties from an unplanned detonation in the proposed Class 1 explosives storage area at the Willows Road tunnel portal entrance site or the underground Class 1 explosives store in the WUG. The likelihood of this event is minimised through site design, restricted access by externally certified handlers only, storage in certified magazine units with security monitoring systems and lightning strike protection, availability of fire protection systems and emergency response management measures. The consequence of this event is evaluated quantitatively using the calculated overpressure level at offsite locations in Section 7.3.2.1 and determined to be minor. The consequence of a detonation at the surface Class 1 magazine area to offsite people is limited through provision of a large separation distance to incompatible substances and the boundary. In the WUG, the consequence of a detonation is limited by the depth underground that the storage chambers will be located and the remote location of the exhaust vent at the surface.
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