5 Tonkin & Taylor Ltd Wharekirauponga Underground Mine – unplanned detonation air quality assessment Oceana Gold New Zealand Limited June 2022 Job No: 1015212.2000 vRev0 2.3 Existing air quality The only anthropogenic air emission sources within this the Coromandel Forest Park are the exploratory drilling activities undertaken by OGNZL, which will represent very minor combustion product sources in the otherwise pristine area. Although there is no ambient monitoring data available, the air quality at this location is expected to be very high quality, consistent with rural locations with few sources of industrial, transport or domestic air emissions. Other surface connections at Willows Road and Waihi are a significant distance from the potential source of the detonation and air quality at these locations is not expected to be impacted. 3 Description of activity and nature of discharges 3.1 Description of explosives storage The proposed underground Class 1 explosives storage facility is to be situated 380 m below the surface, with six separate chambers each holding up to 1,000 kg Net Explosive Quantity (NEQ) of high explosives as detailed in Section 2.2.2 of the HSA. A seventh chamber is dedicated to initiating explosives, containing up to 100,000 units (or 100 kg NEQ). The proposed layout of the storage facility is shown inFigure 3.1below. Figure 3.1: Magazine chamber layout including separation distances and proposed stored quantities’ Source: GSS 2021 The separation distances between the different explosive types have been compared by GSS with those established in accordance with Annex M of theInternational Ammunition Technical Guideline, Quantity and separation distances published by the United Nations Office for Disarmament Affairs (UNODA) in 2015. OGNZL advises that the separation distance between the chambers containing 1,000 kg of Class 1 explosive meet the calculated minimum at which blast propagation between chambers is unlikely. 3.2 Nature of discharges The mine ventilation modelling software package Ventsim has been run by Entech and provides gas yields for detonation of Ammonium Nitrate Fuel Oil (ANFO). Ventsim identifies the following hazardous gases as the main products of combustion: Carbon monoxide (CO), which is a poisonous and flammable gas. Explosives storage facility exit I.E Chamber (up to 100,000 units or 100 kg NEQ) 6 x individual H.E Chambers (up to1,000 kg NEQ each) Explosives storage facility entry 10m
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