Hilbert Libres1, Andrew Martin1, and Kyle Gilchrist2
1 Trinity Consultants Australia
2 Air Quality Support
Abstract – The operator of a manufacturing facility with discharges to air and water has found elevated heavy metals concentrations in adjacent waterways. The regulator raised concerns about deposition from air emissions and used some calculations based on overseas data to suggest that the anticipated concentrations of air emissions would cause high concentrations in waterways. Trinity Consultants Australia undertook modelling of dry and wet deposition to the catchments and calculation of runoff concentrations to provide a site-specific estimation of anticipated concentrations in water. In addition to the site itself, four different catchments were identified and downstream concentrations predicted for each. Wet deposition was found to be far higher than dry deposition. The model predictions were lower than most measured water concentration results but demonstrated that the highest measured results were unlikely due to current site emissions. On-site surface swab measurements also assisted interpretation of results. Model predictions of deposition have high cumulative uncertainties propagated from, for example, emission rates, dispersion, particle sizing, deposition parameters, and rainfall (for wet deposition). Additional uncertainties in the catchment modelling include the use of rainfall to calculate dilution, and uncertainties in the flow direction across some industrial sites. Fugitive emissions are generally difficult to quantify and may lead to substantial deposition close to the site. Contamination entering waterways from historical ground contamination have also not been included in this assessment. However, the results are useful in providing order of magnitude estimations of absolute concentrations and more accurate estimates of relative impacts of the different sources and onto different catchments.
Presented at the The Clean Air Society of Australia and New Zealand (CASANZ) 28th International Clean Air and Environment Conference and the Asia-Pacific Odour Conference in Cairns, Queensland, on 31 August to 2 September 2026.