46 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 8 Assessment of effects 8.1 Introduction The following assessment identifies and assesses the actual and potential effects of the proposed hazardous substances storage and use as part of the development and operation of the Willows Road tunnel portal entrance site and the WUG. This assessment also outlines the measures that OGNZL proposes to avoid, remedy or mitigate any potential adverse effects on the environment. 8.2 Hazardous substances In accordance with the Objectives and Policies of the HDP, the assessment has particular regard to the following aspects: Adoption of a low-risk approach and avoiding as far as practicable the risks associated with the production, storage, use, conveyance and disposal of hazardous substances; Ensuring that hazardous substances are used, handled and conveyed through the district in such a way to avoid adverse environmental and health effects; Discouraging the production of hazardous waste, and avoiding unsafe discharge or disposal of hazardous waste to the environment; and Recognition of industry and operator codes of practice. 8.2.1 Effects on people and property The Willow Rd site is situated in the Rural zone, with the mining tunnel extending into the Conservation (Indigenous Forest) zone under the HDP. The risks to people and property are from a fire at the bulk stores of hazardous substances, including the explosives magazines and oxidising agents stored at the surface near the portal and underground in the mine. Class 1 explosive substances are proposed to be stored in six H.E. magazines and one I.E. magazine at the surface. The same number of individual storage chambers are proposed for the underground store. Each magazine or underground chamber will be separated by an offset distance that mitigates the risk of inter-magazine propagation per industry standard AS 2187.1, Table 3.2.3.1. When considering the consequence of an unintended detonation at the explosive storage areas, overpressure zones have been conservatively estimated by GSS for one H.E. magazine and the I.E. magazine, equivalent to an individual magazine of 1,310 kg NEQ for the surface facility and 1,100 kg NEQ for the underground facility. These overpressure zones enable a quantitative consequence analysis for the impact of an unintended initiation. As discussed in Section 5.2 for the surface magazine, there are areas of neighbouring rural and conservation land that fall within the 2 kPa blast overpressure radius of the magazine. While there are currently no dwellings in the area of overlap, there are no restrictions on dwellings being established in future on the rural property. Under the HSW-HS regulations, there are no restrictions on buildings with fewer than 4 storeys in the 2 kPa – 9 kPa radius area unless they are being used for hospitals, early childcare centres or vulnerable facilities of similar scale. Small areas to the north of the Willows Road site in the Conservation (Indigenous Forest) zone also fall within the 2 kPa blast overpressure radius of the surface magazine compound. There are no residential units or public walking tracks in this area, however it is feasible that a person could be present at this location. In the event of a detonation in the underground explosives storage facility, overpressure is expected to exhaust at five surface vent locations identified in Section 5.3. All surface vent locations are located on either OGNZL owned land or within the legal road reserve with suitable public access
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