| Existing Air Quality Effects | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 39 6 Existing Air Quality Effects 6.1 Potential for Dust to Cause Adverse Effects Dust deposition is the settling of dust onto surfaces. The effects of dust deposition can be subjective and are dependent on the sensitivity of the receiving environment. Some people will not be annoyed by dust, others will be annoyed, and some may find it objectionable or offensive. Dust fallout on a road or rural farmland may not be a nuisance even at relatively high deposition rates. Typically, the most common areas of concern from dust deposition arise at residential properties (or similar sensitive locations such as retail premises or schools) and include the visual soiling of clean surfaces, such as cars, window ledges, and household washing and dust deposits on vegetation. The GPG Dust34 notes that the potential for a dust discharge to cause an objectionable or offensive effect depends on the following characteristics of the dust fallout: ● The frequency of dust nuisance events ● The intensity of events, as indicated by dust quantity and the degree of nuisance ● The duration of each dust nuisance event ● The offensiveness of the discharge having regard to the nature of the dust (e.g. colour, odour, stickiness) ● The location of the dust nuisance, having regard to the sensitivity of the receiving environment. These are known as the FIDOL factors and are also used in odour assessment to consider whether an odour discharge has caused an offensive or objectionable effect. Essentially, whether a dust discharge leading to dust deposition causes an offensive or objectionable effect depends on how frequent it is and how much dust is deposited. Dust deposition is typically measured over a period of about 30 days using a dust gauge. However, this does not mean that dust deposition occurs gradually and evenly over that 30-day period. Dust concentrations in the ambient air downwind of a dust discharge vary with the rate of dust emission and the wind conditions. Therefore, the rate of dust deposition varies as well. It is possible that the majority of the dust deposition measured in a 30-day period by a dust gauge occurs during a small number of short, relatively high-rate deposition events, or it may occur at a relatively constant rate throughout the month. Short term events of relatively high-rate dust fallout are more likely to be noticed by residents as deposits on surfaces, cars and washing. TSP monitoring measures particles that are suspended in the air. Most monitoring equipment collects particles that vary in size between 0.1µm and about 100µm. The finer fractions can travel large distances downwind before they reach ground level. The larger fractions of TSP can have nuisance effects but the perception of potential for TSP to cause health effects is usually the cause of most concern for nearby residents. 34 Ministry for the Environment: “Good Practice Guide for Assessing and Managing Dust” 2016.
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