| Potential Effects of Project on Environment | WNP Wharekirauponga Underground Mine - Assessment of Effects of Discharges to Air | 4397169-66885702-23 | | 47 7.7.3 Respirable crystalline silica There may be some potential for variation in crystalline silica content in rock mined from the WUG Mine and therefore its potential to increase the respirable crystalline silica (RCS) content of airborne particulate matter in the Willows Road area. Mechanical crushing is not proposed at the Willows Road site but some minor amounts of finer dust, that may contain RCS, may still be generated at the rock stacks and during materials handling and from vehicle movements on unpaved WRS roads. Topsoil material which will be stored closer to existing dwellings on Willows Road will not be a significant source of RCS. RCS has not been measured in ore to be mined at the WUG site. However, silica concentrations (24-hour average) around the Waihi site, based on OGNZL monitoring until the end of 2014 and continuous monitoring by Waikato Regional Council (WRC), between 2008 and 2011, were well within health-based guidelines28. Respirable silica concentrations did not exceed the OEHHA annual average guideline level of 3 µg/m3 and monitoring was subsequently ceased as the WRC considered that ambient air quality within the Waihi Airshed (and notably downwind of the Martha Pit) did not pose any significant potential health risks. The monitoring also indicates that 24-hour average concentrations were also typically less than the annual average guideline level. Monitoring work carried out at Yaldhurst near Christchurch29 by Mote Ltd provides useful information on the assessment of the likely effects of RCS from the discharge of dust at Willows Road. The ambient air concentration of RSC was measured at six locations in the vicinity of seven operational quarries for a period of 4 months. The monitoring site were located between 50m and 650m from the quarries. Monitoring also occurred at two background sites Unlike the Willows Road project, quarry operations include mechanical crushing of aggregate which is a potential source of dust that may contain RCS. Therefore, the results at Yaldhurst would represent a worse case than would be expected at Willows Road. The concentrations of RCS were compared with the California Office of Environmental Health Hazard Assessment (OEHHA) guideline of 3µg/m3 (annual average). This guideline is recommended for assessing the long-term effects of RCS exposure. The study showed that only two of twenty samples recorded RCS above the level of detection and that the average concentration of these sample was 0.4 µg/m3 (only 13% of the OEHHA guideline value). The two results above the limit of detection occurred at the 50m downwind site. The Mote study demonstrated that the RCS concentrations downwind of an operating quarry using mechanical aggregate crushing equipment can be elevated above background concentrations but are well below the recognised health guideline value. The study highlighted the need for effective dust control to be carried out, especially when extraction and crushing operations occur within 100m of downwind dwellings. The Canterbury Medical Officer reviewing the study results noted: “Overall, the results show there is no serious public health risk to Yaldhurst residents from airborne dust. Nuisance dust levels will not cause long term health effects, but we know it can cause irritation and symptoms of concern in some people”. 28 From Waihi Gold Annual Monitoring Report 2014 29 Mote Ltd (2018) Yaldhurst Air Quality Monitoring Summary Report 22 December 2017 – 21 April 2018, report prepared for Environment Canterbury
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