33 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 The cyanide management plan12 outlines the cyanide processes within the Processing Plant, transport of cyanide to the mine, handling and storage requirements, monitoring sensors and testing undertaken, site water management and protection measures for workers, equipment and the environment. Where cyanide is used in the Processing Plant, the control systems are automated where possible, to enable automatic dosing and mixing and minimise worker contact. Interlocked control systems are in place to prevent tank overflows and avoid uncontrolled releases. Possible overflow locations are identified and bunded to provide secondary containment control in the event of a spill. Rainfall is directed away from the bunded areas to prevent effective reduction in bund capacity. As an additional layer of protection, if there was a bund failure, any release would be contained within engineered ponds on-site. OGNZL keep bags of ferrous sulphate on site to be used to precipitate cyanide out of solution and detoxify any cyanide spills. This can be dosed to the secondary or tertiary containment as part of the emergency response measures. A site-specific cyanide emergency procedure is provided as Appendix M of the WEMP which outlines the hazards, symptoms of poisoning, PPE required, medical and first aid requirements, and instructions for response to small and large spill instructions and fires.OGNZL has a solid cyanide mixing and tank transfer procedure13 in place for trained employees and contractors. The procedure requires two persons to be present at all times and both persons must be wearing a cyanide monitor prior to opening the storage shed and during operations. The procedure outlines the required personal protective equipment (PPE) which include respirators, chemical suits, chemical resistant rubber boots in addition to standard minimum site PPE. A pre-start checklist is provided prior to starting works including windsock operational condition and safety equipment operation. 4.11.2 Corrosive liquid delivery, storage and use Corrosive liquids on-site include the hydrochloric acid and caustic soda used in the Processing Plant. As specified in the HSMP the hydrochloric acid and caustic soda are isolated and contained in separate bunds, each with splash guards for pumps, tanks and pipes. Both the hydrochloric acid and caustic soda systems are engineered to maximise automated controls and instrumentation to avoid human contact. Automated processes include automated re-ordering to prevent overfilling of tanks. Each tank is certified as a compliant stationary container system under the HSW-HS by an independent certifier. The delivery point to both tanks is secured with a unique key and lock system to prevent delivery errors. 4.11.3 Quicklime dust control The quicklime silo is fitted with overfill protections such as high-level sensors. The silo has a dust collection system with fabric filters to remove lime particulate from the displaced air released during filling. 12 OGNZL, November 2017, Standard operating procedure Waihi Cyanide Management Plan, WAI-451-PLN-002 13 OGNZL, January 2020 (updated), Solid cyanide mixing and tank transfers (automated) procedure, WAI-451-PRO-006
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