52 Tonkin & Taylor Ltd Hazardous Substances Technical Assessment – Waihi North Project - Waihi Processing Plant, Water Treatment Plant and Development Site Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.1000 vRev0 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 G that was assessed as moderate as follows: Moderate residual risk to the ecosystems from a spill of diesel, through a spill during refuelling or 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 and management provisions including emergency response planning, inspections, spill kits and staff training. All other risks were assessed as low including: Low residual risk to ecosystems from a spill of packaged goods such as maintenance oils and greases during unloading to site. This is managed through physical controls including secondary containment in storage and the tertiary collection ponds to prevent discharges to the environment. Small spills are primarily managed through bunded workshops, staff training and emergency response planning including spill kits at unloading areas. Low residual risk of fire at the diesel, LPG, oxygen and hydrogen peroxide storage areas impacting off site locations. 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 and the site boundary, as well as emergency management measures including fire-fighting facilities and staff emergency response training. Low residual risk to human health or ecosystems from a spill of solid or liquid cyanide, either from a valve failure or tank rupture. This is managed through physical controls including bunding, isolation of the cyanide systems away from the boundary or sensitive activities and automation of the systems handling cyanide, management measures including staff training in task specific procedures and emergency response, provision of spill kits, and as a final emergency control, provision of collection ponds for retention of spills on site in the unlikely event of a bund overflow. Low residual risk to human health or ecosystems from a spill of bulk hazardous liquids (hydrated lime, hydrogen peroxide, hydrochloric acid or caustic soda) from a valve or hose failure or a tank leak. This is managed through physical controls including tank bunding, automated process control systems and management controls including independent certification of storage locations. The consequence of a spill is managed by separation distances from the tanks systems to sensitive activities and the boundary, emergency response planning and staff training. Low residual risk to human health or ecosystems from a spill of mercury at the gold room. This is managed through physical controls including provision of secure, bunded containment for the mercury retort system, and separation of this system from sensitive activities or the boundary, and management controls including minimising inventory of mercury by regularly removing it from site for safe disposal, restricting access to trained and certified handlers, provisions of emergency response procedures and environmental monitoring. Low residual risk to occupants of off-site properties from an unplanned detonation in the proposed Class 1 explosives storage area at the Development Site. The likelihood of this event is minimised through 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 off site locations in Section 7.3.2 and determined to be minor. The consequence to off-site
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