| Introduction | WNP Processing Plant Air Discharge Assessment | 4397169-66885702-113 | 16/06/2022 | 1 Sensitivity: General 1 Introduction 1.1 Overview Oceana Gold (New Zealand) Limited (OGNZL) operates an open cut and underground gold mining operation at Waihi in the Waikato Region. Ongoing exploration and mine optimisation have identified further mineral resources that can be economically recovered. These new activities are referred to as the Waihi North Project (WNP). OGNZL currently holds a resource consent (consent number AUTH124859.01.04) which permits the discharge to air of contaminants from the existing Processing Plant subject to consent conditions. However, there are features of the proposed WNP which will have an impact on the emissions from this Plant. These include: ● The ore processing capacity will increase from 1.25 million tonnes per annum (MTPA) to 2.25 MTPA ● The mercury content of the ore extracted from the new Gladstone Open Pit (GOP) mine is on average expected to be approximately 3.27ppm, or approximately 11 times higher than the average mercury content of the ore, which is currently processed, of 0.3 ppm ● The mercury content of the ore extracted from the new Wharekirauponga Underground (WUG) mine will is expected approximately 0.6 ppm, or approximately 2 times higher than the average mercury content of the ore which is currently processed. Overall, emissions of mercury and other trace metals from the Processing Plant would be expected to increase because of the WNP and therefore make a greater contribution to ambient air quality concentrations beyond the site boundary. OGNZL has commissioned Beca Ltd (Beca) to undertake a technical assessment of the effects of the discharges from the Processing Plant as a result of the proposed WNP. 1.2 Scope of Report This report provides an assessment of the proposed discharge of contaminants (metals) in emissions to air from the Processing Plant. The primary contaminant of concern is mercury which is emitted during smelting and the carbon regeneration processes. The effects that plant emissions will have on air quality, as a result of the proposed WNP, have been assessed using atmospheric dispersion modelling methods. The CALPUFF air dispersion model has been used to predict the maximum ground level concentrations of contaminants and the potential impacts have been assessed by comparing the predicted contaminant concentrations against relevant air quality criteria. Discharges from the Processing Plant’s electrowinning stack, combined oven/furnace stack and carbon regeneration stack have been included in the model. Specifically, this report includes the following: ● A description of the nature of the discharges to air from the Processing Plant ● A summary of the dispersion modelling methodology ● A summary of relevant air quality criteria ● A summary of the results of the assessment of effects on air quality ● Conclusion and recommendations. 1.3 Limitations This report has been prepared by Beca for OGNZL. Beca has relied upon the information provided by OGNZL in completing this document. Unless otherwise stated, Beca has not sought to independently verify
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