In response to community concern about the levels of visible black dust in the lower Hunter region, and at the request of the Newcastle Community Consultative Committee on the Environment, the EPA commissioned a study to examine quantity, composition and likely sources of this dust.
The EPA established the Lower Hunter Dust Deposition Project Reference Group (PRG) for the study. It comprised eight members including community, industry and the EPA representatives and technical experts. The PRG met between April 2014 and February 2015.
Lower Hunter Dust Depositions Study
Following a competitive tender process, the EPA in consultation with the PRG, commissioned AECOM to undertake a one-year monitoring program to assess dust composition and deposition rates. Through the PRG, expressions of interest were sought from community to identify dust monitoring locations over a one year period. Twelve representative sites were selected.
Dust samples from the 12 dust deposition gauges were taken and analysed between October 2014 and October 2015. Results of the composition identification analysis identified:
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Soil or rock (primarily aluminosilicate) as the primary source of deposited dust averaging 69% of all samples with a range of 40% to 90%.
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Insect and plant debris accounted for an average of 10% of all samples with a range of 0% to 40%.
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Coal on average formed 10% of total deposited dust with a range of 0% to 25%.
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Rubber dust on average made up 4% of total deposited dust with a range of 0% to 20%.
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Soot accounted for an average of 3% of all samples with a range of 0% to 20%.
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The remainder of the deposit dust was largely comprised of halite (salt), fly ash, alumina, paint and miscellaneous fibres.
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Deposited dust within the study area is comprised of approximately:
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69% soil and rock dust; equating to a deposition rate in in the order of 0.35 to 0.76 g/m2.month;
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17% black particles (coal, soot and rubber); equating to a deposition rate in in the order of 0.09 to 0.19 g/m2.month; and
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14% other material (including insects and vegetation); equating to a deposition rate ranging from 0.07 to 0.15 g/m2.month.
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Annual average dust deposition was found to be below the EPA 4g/m2.month maximum dust deposition criterion for all sites, ranging from 0.5 g/m2.month at the Newcastle monitoring location to 1.1g/m2.month at the Islington location. The highest levels of coal deposition were generally observed around Stockton and Newcastle East, and closer to the rail line around Wickham, Hamilton and Tighes Hill. However, the contribution of coal was highly variable – some samples yielded little coal when downwind of potential sources.
Analysis of soot contributions indicated higher deposition rates around Stockton, when downwind from the industrial areas of Mayfield, Carrington and Kooragang Island and the shipping channels and berths within the harbour, though some variability was present between samples. The rubber dust results did not indicate any significant trends and were attributed to tyre degradation along arterial and local roads.