| Existing Air Quality Effects | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 44 Figure 6-3 Monthly average deposited dust monitoring rate (g//m2/30-days) (January 2000 – December 2020) The MfE GPG Dust notes36 that “general dust deposition levels in New Zealand range from about 1 – 4 g/m2/30 days. Background concentrations are usually less than 1 g/m2/30 days but there are also areas (such as Central Otago) where the natural dust levels can be up to 10 times this amount”. The dust levels measured in the vicinity of the site are within the range of typical dust levels measured in New Zealand, and on average generally representative of general background levels. A statistical analysis of the monthly deposited dust rates recorded at each of the sites was conducted using a pairwise Wilcox Rank Sum test37. The test compares the deposition rate recorded at each monitoring site against all the other sites in a pair-wise manner38. The test was used to assess whether there was a statistical difference between the distribution (and median) of the deposition rates recorded at each of the different sites. The methodology and results for this analysis are provided in Appendix D. Sites 6.60 (Torrens, Town End) and 6.59 (Torrens, Alexander) are both located in rural areas and are not downwind of the mining operation in the prevailing wind conditions. Dust levels measured at these sites are considered to be representative of background levels. No significant statistical difference was detected 36 Ministry for the Environment “Good Practice Guide for Assessing and Managing Dust” 2016 37 The Wilcox Rank Sum test is a non-parametric test. The test was used because the distribution of the site deposition rates was determined to be non-normal, therefore parametric tests such as the T-test are not considered appropriate. 38 The Bonferroni method was used to adjust the predicted p-value to account for the change in the probability of a significant difference being detected due to the number of statistical tests which are performed during this procedure. 0.0 2.0 4.0 6.0 8.0 10.0 12.0 Monthlt Average Deposition Rate (g/m2/30-days) 6.59 (Torrens opp Alex) 6.60 (Torrens Town End) 6.61 Leaches (Grey Street) 6.63 (Met Station) 6.66 (College) 6.7 (Smith) 6.71 (Morrison) 6.72 (Baxters Road) North Wall Collapse Trigger Level (4 g/m2/30-Days)
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