13 Tonkin & Taylor Ltd Wharekirauponga Underground Mine – unplanned detonation air quality assessment Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.2000 vRev0 Table 5.3: Evaluation of GLCs against assessment criteria Contaminant Assessment criteria (µg/m3) Highest GLC (µg/m3) Predicted location Background concentration (µg/m3) Cumulative GLC (µg/m3) IAQM impact descriptor CO 30,000 459 (1.5 % of criterion) 130 m NE of vent 5,000 (16.7% of criterion) 5,459 (18.2% of criterion) Negligible NOX (as NO2) 200 59.9 (30% of criterion) 130 m NE of vent 37 (19% of criterion) 96.9 (48% of criterion) Moderate NH3 21,000 19.5 (0.09% of criterion) 130 m NE of vent 0 (0% of criterion) 19.5 (0.09% of criterion) Negligible 5.5 Scaling results for other explosive types The modelled emission rates were developed for a detonation of 1,000 kg NEQ of ANFO in the WUG explosives store. There are three explosive types expected to be stored in these chambers: ANFO, boosters and packaged explosive. The packaged explosive is an ANFO based explosive for which the ANFO detonation scenario can be considered representative. However, the boosters have a Trinitrotoluene (TNT) base (containing up to 80% TNT content). Therefore, we have also included consideration of the impact on air quality from a detonation of 1,000 kg NEQ of TNT based explosives. Explosives manufacturer Orica has provided the detonation product breakdown for the boosters, which indicates that where 1,007 m3 of gas is produced in a detonation of 1,000 kg NEQ, only 672 m3 of gas would be expected for the same mass of booster (Table 5.4). Table 5.4: Products of combustion by explosion type Gaseous product Yield m3 per kg NEQ at 0°C, 1 atmosphere ANFO Booster CH4 methane 4.614 0.159 CO carbon monoxide 38.0 67.6 CO2 carbon dioxide 92.724 250.3 H2 hydrogen 0.069 1.9 NH3 ammonia 1.0 58.7 H2O water 604.2 178.7 N2 nitrogen 263.2 114.8 NO nitric oxide 1.5 0.381 NO2 nitrogen dioxide 1.5 - O2 oxygen - 0.008 Total volume of gas produced (m3) 1007 672 The comparative yields for the contaminants of interest in the model are presented inTable 5.5 below. A yield of NO2 was not provided for the TNT booster product, so consideration of the comparative yield of nitrogen gas was also included in the comparison below to approximate the yield of NO2.
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