| Discharges to Air and Associated Mitigation Methods | Waihi North Project Air Discharge Assessment - Waihi Surface Facilities | 4396626-1331619777-99 | 16/06/2022 | 22 Exposed surfaces such as those on stockpiles, noise bunds, and TSFs are all potential sources of dust unless they are appropriately controlled. The primary means of controlling dust from sources such as these is by revegetation wherever practical and keeping surfaces damp. Minimising the quantity of fine particles on the surfaces exposed to wind also reduces dust potential. The methods used by OGNZL to minimise the generation of dust from exposed surfaces and which will continue to be used for the WNP include the following: ● Keep operational areas around the pits, stockpiles, Processing Plant and haul roads damp using water tanker vehicles when required ● Use screens and fences to prevent wind-blow in dust prone areas ● Vegetate the outer walls of the noise bunds, TSFs and NRS as soon as practicable. Historically, the surfaces of the TSFs have not been a source of dust at Waihi and this is expected to continue to be the case. During normal operation of the TSFs, sections of the tailings are rested while other sections continue to receive fresh tailings from the Processing Plant. The fresh tailings are wet and the placement of them on the surface of the impoundments suppresses the release of dust. Due to the relatively high rainfall at Waihi, the sections of the impoundments that are allowed to rest do not tend to dry out sufficiently to become subject to wind erosion. Crushing and screening plant Crushing and screening of rock has the potential to generate dust if it is not controlled. The most effective means of controlling dust generated from these activities is the use of water to keep the materials damp. To control the dust, OGNZL will use the following mitigation measures on the new crushing plant and on the existing equipment: ● Water sprays on the new modular crushing plant at the Processing Plant will be used to control dust ● Use irrigation sprays on crushers and conveyor transfer points to control the moisture content of materials ● Minimise drop heights from the loading of raw materials into the feed hoppers and from stacking of stockpiles. Drilling Drilling rock surfaces has the potential to generate dust. The blast hole drilling rigs are fitted with dust collectors and bag filters, which are maintained in good condition in accordance with the manufacturer’s recommendations. The exploration drills use fluid lubrication and produce negligible quantities of dust. Application of limestone to potentially acid forming rock To neutralise the formation of acid from overburden, OGNZL spreads crushed limestone on the surface of the rock stacks and active construction areas on the TSF embankments when necessary. Limestone includes a proportion of fine powder that can be easily carried in the wind. To minimise the spread of limestone onto neighbouring properties, OGNZL will not apply limestone when winds are strong and blowing towards neighbouring properties.
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