11 Tonkin & Taylor Ltd Wharekirauponga Underground Mine – unplanned detonation air quality assessment Oceana Gold (New Zealand) Limited June 2022 Job No: 1015212.2000 vRev0 5 Model results 5.1 Introduction The GLCs predicted using dispersion modelling have been used to assess the effects of contaminants by comparing predicted off-site concentrations, added to background concentrations, against relevant assessment criteria. Background concentrations of NO2 and CO are based on published background levels for non-urban areas, detailed in Section 5.2 below. 5.2 Background concentration Ambient background concentrations are added to the modelled GLCs to present the total ambient concentrations for each contaminant. Representative 24-hour background levels are provided for rural areas in Waka Kotahi’s background air quality map4 and Auckland Council’s Use of Background Air Quality Data in Resource Consent Applications Guideline Document5(GD 2014/01), as recommended in the GPG Industry guidance. In practice, background concentrations in the forest area will better than expected of a rural area. Accordingly, we consider that these default background concentrations are likely to significantly overstate existing air quality in a pristine forested location. Table 5.1: Applicable background concentrations Contaminant Averaging period Background concentration (µg/m3) Source CO 1-hour 5,000 Auckland Council for rural areas NO2 1-hour 37 Waka Kotahi for rural areas There is not expected to be an appreciable background level of NH3 in the forest reserve. 5.3 Assessment criteria Assessment criteria have been adopted based on the hierarchy set out in relevant Ministry for the Environment’s good practice guidance (GPG Industry6), and include values from the National Environmental Standards for Air Quality (NESAQ) and the New Zealand Ambient Air Quality Guidelines (AAQG). The relevant human health assessment criteria for emissions of CO, NO2 and NH3 are summarised in Table 5.2 below. Comparison with these concentrations is made to identify potential impacts on human health at proximity to the discharge location. Table 5.2: Criteria for ambient air quality Contaminant Averaging period Concentration (µg/m3) Reference CO 1-hour 30,000 NZ AAQG 4 Waka Kotahi. https://www.nzta.govt.nz/roads-and-rail/highways-information-portal/technical-disciplines/air-qualityclimate/planning-and-assessment/background-air-quality. Retrieved 11 April 2022. 5 Auckland Council. 2014. Use of Background Air Quality Data in Resource Consent Applications. Auckland. 6 Ministry for the Environment. 2016. Good Practice Guide for Assessing Discharges to Air from Industry. Wellington: Ministry for the Environment.
RkJQdWJsaXNoZXIy MjE2NDg3