16 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 Class 5 substances (compressed oxygen in cryogenic tank and hydrogen peroxide) are each located in designated areas. The oxygen has a high fire/explosion hazard due to the volume and oxidising nature of the substance, which will accelerate combustion in the event of a fire. The hydrogen peroxide storage location is at the WTP north of the Processing Plant activities. The hydrogen peroxide also has low human health and environmental hazards in the event of a spill or during handling of the substance (i.e. delivery, storage and use). Mercury has a high hazard to human health and the environment and will be contained in small volumes for safe disposal in the electrowinning building of the Processing Plant. The petroleum substances on-site include diesel, LPG, the maintenance oils and greases used to maintain plant equipment and the oil stored within the transformers in the proposed substation. The maintenance oils and greases are located within the workshop areas. Diesel and some of the maintenance oils and greases have chronic human health hazards. Diesel is also highly hazardous to the environment. LPG is highly flammable, while diesel has a lower flammability rating and is considered combustible. These substances will be stored and used in bunded areas equipped with fire-fighting facilities. The distance between the storage locations in relation to OGNZL’s boundary limits the potential for offsite persons to come into contact with any released material in the case of a spill. The relocation of the LPG tanks will place them in an isolated location central to the OGNZL landholding, providing additional separation to off site locations and other hazardous substance storage. The transformer oil is classified as hazardous due to its hazard to human health in the event that it is inhaled in an aerosol form. This substance is a liquid contained within the substation equipment and therefore does not pose a hazard to off site people. The remaining substances with toxic, corrosive or ecotoxic properties include the acids (caustic soda and hydrochloric acid), cyanide (solid state and in solution), ferric chloride, hydrated lime (calcium hydroxide) solution and quick lime (calcium oxide). The quick lime is stored in a silo west of the Processing Plant and has human health hazards due to the corrosive nature of the substance and low ecotoxicity hazards. However, it has a limited pathway to offsite sensitive receptors due to the storage as a powder in silos at a large distance from the boundary of OGNZL owned land. Ferric chloride and hydrated lime solution are stored in tanks at the WTP and caustic soda in bunded tanks west of the electrowinning area. These liquids present a low hazard to human health via ingestion, as well as being corrosive to skin and eyes. The separation of these substances to the boundary limits their potential impact at off site locations. The acids and cyanide have a high hazard rating with regards to human health and the environment. These are stored and used in bunded areas central to the site and are automated with interlock systems and auto re-ordering abilities to reduce human interaction and overfilling. Further controls relevant to these substances are discussed in Section 4. The compressed carbon dioxide in the tanks at the WTP is not classified as hazardous and does not present a hazard to off site receptors. This substance has not been considered further in this assessment. 3.5.3 Development Site – New Class 1 explosives store The volumes, classifications and location of explosives associated with the Development Site are set out inTable 3.2 below.
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