Dust
Prediction
During the planning of any quarry or processing plant the operator is required to prepare an Environmental Impact Assessment study, which includes an estimate of the potential predicted dust emissions to the surrounding environment. Dust emission, dispersion patterns and impacts are difficult to predict due to the wide range of activities on site that may give rise to dust, the lack of reliable emission factors for these activities, and the influence of local meteorology and topographic features. Computer modelling can provide crude predictions of likely dispersion patterns, and various dust monitoring techniques can provide an understanding of possible levels of dust that may be deposited in and around a site.
Most environmental regulatory authorities require the operator to submit an audit and assessment of the dust emission sources during the projected lifetime of the operation, and to detail the mitigation measures that will be enacted to minimise any off site dust emissions. The predictions require a dust emission estimate for each of the static and mobile fugitive dust sources planned within the mining, and associated materials transport and downstream mineral processing operations. Currently, most estimates are based on the US EPA dust emission estimates AP-42 L0300, although the US NSSGA L0299 have also published data which is available to purchase. These dust emission estimate models are then included as source input data to a suitable plume dispersion model such as UK-ADMS (Atmospheric Dispersion Modelling System).
A description of the various types of air pollution models which are available is given in the ALSF Review L00??L0089, while a comprehensive review of the dust dispersion models relevant to quarries and other surface mines is also available 453.
Two recent MIST sponsored research projects, L0076 L0078 have conducted a series of preliminary dust dispersion measurement and modelling studies at a major UK limestone quarry. They used ADMS which is approved for use by the UK Environmental Agency and is typically employed in assessments supporting Pollution Prevention and Control (PPC) applications, to determine suitable discharge conditions such as stack height, requirements for pollution control systems and for safety planning. The aim of these studies was to develop a modelling strategy to simulate dust dispersion from blasting events and haul roads applicable to UK hard rock aggregate quarries 455.
These models are still of limited application to surface mining operations as they are unable to adequately model terrain with slopes greater than one in three. They therefore do not take into account the additional fall out and impaction experienced by dusts due to secondary in-pit meteorology (air recirculation movements) and so they over predict the dust emissions. A series of field experimental studies were conducted by the EPA in the US to estimate the retention of the dust emitted within shallow coal strip mines and quarries. They concluded that between 30 – 50% of Total Suspended Particulate (TSP) matter and 5% of PM10 matter were retained within the pit due to additional dust drop out.
However, the second MIST project L078 was able to adapt the ADMS modelling software to replicate the dust emission, dispersion and deposition observed in the field during blasting and haulage operations on a large limestone quarry. It still requires detailed and accurate on-site meteorological records in order to provide satisfactory results.
Other research projects summarised in the ALSF Review on Dust L0089 (Part 3: Section 3) have looked at emission and dispersion from various quarry activities, in order to better understand the processes involved and therefore provide better predictive models.
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