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Determination of Limit Values for Deposition of Dust and Regulation of Dust Emissions from Fugitive Sources

Summary and conclusions

The Danish Environmental Protection Agency initiated this project in 2002 with the objective of proposing a national guideline for the deposition of dust around fugitive sources such as stockpiles of particulate matter. This report recommends a guideline based on what is expected to be a representative “trigger level” at which nuisance from visible dust deposition can be expected among the neighbouring communities.

In most cases, dust nuisances can be avoided through properly defined terms of operation. There are at present no general guidelines in Denmark for the management of fugitive sources of dust such as stockpiles. The report describes general terms of operation that can be used in connection with dust management at industrial activities involving stockpiles of particulate matter.

The need for a guideline for dust deposition occurs where problems of dust nuisance persist in spite of the specified operating terms.

The general background of dust deposition and emissions from fugitive sources is described. Determining factors for the emission of dust from e.g. stockpiles are the particle size, the density of the particles, and the moisture of the stockpile. Furthermore, the emission is highly dependent on meteorological parameters such as wind speed and precipitation.

Criteria for a dust deposition guideline
In Denmark, most complaints about nuisance from dust occur due to stockpiles containing particulate matter. The guideline for dust deposition proposed in this project is based on the highest acceptable dust deposition rate, defined as the “trigger level”, where nuisances occur due to the deposition of visible dust on surfaces. Other possible effects of dust deposition - such as effects on health or ecosystems – are not included as criteria in this project. The Danish EPA has not issued guidelines for the deposition of toxic compounds. German guidelines for the deposition of metal compounds are found in annex A.

The proposed guideline is to be used in connection with the regulation and control of dust from fugitive sources. The Danish EPA has issued guidelines for air emissions based on the regulation of the maximum contribution from industrial plants (C-values) /7/. In line with the criteria for C-values, a high priority has been given to criteria for dust deposition based on the maximum acceptable contribution from a given source/industrial plant.

Dust deposition is often classified in two fractions: Dissolved and insoluble matter. Outdoor stockpiles will almost always consist of particles that are insoluble in water. It is recommended that a Danish guideline for dust deposition be based on insoluble dust. A guideline for insoluble dust deposition will cover most situations, where nuisances due to deposition of visible dust on surfaces occur.

It cannot be excluded that nuisances may occur due to deposition of water-soluble particles at certain industrial plants. Water-soluble particles may occur in emissions from point sources, e.g. where bag filters break, or in fugitive emissions from open doors or windows at plants using indoor installations, or where sea water is used for sprinkling. Dust deposition from these sources can normally be reduced sufficiently by remedial actions, and by definition of appropriate terms of operation. If needed, a guideline for the sum of insoluble and soluble dust should be developed, based on the trigger level acceptable for the site in question.

The guideline is proposed on the basis of experience gained with dust deposition in Danish background areas, on the basis of cases where elevated dust deposition has been reported around fugitive sources such as open stockpiles, and on the basis of a review of existing national guidelines for dust deposition.

Experience from background areas and areas around fugitive sources
From measurement campaigns, it is estimated that the normal dust deposition rate in Danish background areas – i.e. outside urban areas and areas with heavy traffic – is 0.02 g/m²/day or less, measured as insoluble dust and as a monthly average.

A series of cases, where dust deposition were measured around open stockpiles, were assessed. Due to the quite high variation in the natural background, attempts were made to correct the total dust deposition for the background found in the area in question. The total dust deposition in the vicinity of the sources was generally between 0.06 g/m²/day – 0,1 g/m²/day, measured by means of bulk samplers. These figures are found in inhabited areas 300 metres or less from the source.

It was possible to calculate the contribution from the stockpiles in a few recent cases where a newly developed wind directional dust deposition sampler was used. The following results are given for insoluble dust. Around coal piles, a contribution of maximum 0.06 g/m²/day was found on a location placed 300 metres from the piles. This contribution was found from monthly measurements over seven months, and by only measuring the dust deposition, when the wind came from the coal piles. The dust deposition measured was corrected for the background level in the area, measured in parallel. During the measurement period, no complaints were received from the neighbouring community near the coal piles. In the same way, the contribution from a gravel pit was calculated to be 0.15 g/m²/day – 0.16 g/m²/day by measurement over a period of three months with a wind directional dust deposition sampler. In this case, complaints were reported from the neighbouring community.

Review of national guidelines for dust deposition
There are national guidelines for dust deposition in a number of countries. In most of these countries, the guideline is based on insoluble dust. The guideline in these countries varies from 0.10 g/m²/day to 0.33 g/m²/day as yearly averages. A few countries such as Germany, Austria and Switzerland, have defined guidelines for the sum of insoluble and soluble dust.

With a few exceptions, the guidelines are defined as the total amount of dust deposited, i.e. correction for the background level is not required. However, New Zealand has in 2001 issued recommended “trigger levels”, based on the maximum amount of dust deposited above the background deposition /15/. The recommended guideline in New Zealand is 0.133 g/m²/day as a maximum increase above the background deposition. Corresponding to this, the Environmental Authorities in New South Wales in Australia has suggested a maximum contribution to the background dust deposition around stockpiles of organic matter such as dust from untreated wood /46/.

Proposed guideline
It is concluded that the guideline of 0.133 g/m²/day for insoluble dust as recently recommended in New Zealand can be used under Danish conditions. This guideline describes the highest acceptable contribution to the background level from a given industrial source of dust. The guideline in New Zealand corresponds well to what is expected to be a representative trigger level for the perception of nuisance from dust deposition, i.e. the accumulation of visible dust on surfaces.

The Danish guideline is proposed on the basis of the monthly deposition above the background level of deposition, and it is suggested that the guideline is controlled by means of wind directional sampling. It is recommended that the control period and the averaging time of the method for control is defined when more knowledge has been obtained on the consequence of using the wind directional sampler. It is recommended that this knowledge is obtained by more long-term measurement campaigns at specific industrial plants. By wind directional sampling, dust deposition is only collected when the wind is coming from the source, and therefore the actual averaging time can vary from month to month.

It is emphasized that in this study the control of the C-value, i.e. the maximum contribution of air pollution from industrial sources to the ground level concentration, is performed in ambient air. According to the Danish EPA’s Guidelines for air emission regulation /7/, C-values are normally enforced by monitoring the emission from the source, and by subsequently using dispersion modelling to calculate the concentration at ground level. In the case of dust deposition from fugitive emission sources, it is difficult and mostly impossible to perform sufficiently accurate emission measurements. That the dust deposition is only measured during winds from the source is found to be in line with the principles of the Danish EPA’s guidelines for air emission regulation.

As the measured, averaged dust deposition per day will express the total deposition during winds from the source in the month in which the measurement was performed, the varying averaging times are not considered to constitute a problem in relation to monitoring of the contribution from the source.

For installations and facilities with fugitive emissions such as stockpiles, it is recommended that the environmental authorities define a limit value for dust deposition along with the defined terms of operation. A future limit value can be enforced, in case persistent complaints of dust nuisances are made in the neighbouring community.

Environmental authorities should introduce site-specific guidelines, if necessary. Site-specific guidelines might be developed for types of dust that cause nuisances at a lower trigger level, i.e. dust consisting of highly visible particles.

It is emphasized that the guidelines should not generally be monitored around fugitive sources of dust. The guideline is recommended as a tool for environmental authorities and industries in cases where complaints of dust nuisance are made, and where there is a need to assess whether more efficient dust management plans should be implemented.

Recommendation of monitoring method
In relation to the control of a guideline for dust deposition, principles of available monitoring methods are described in the report. Several bulk sampling methods are available. Bulk sampling methods sample dust deposition in the entire measurement period and during all wind directions. Bulk sampling is suitable for assessment of the general dust deposition in an area, but to determine the contribution from a specific source, wind directional sampling is recommended. Wind directional sampling methods include methods that sample dust during specific wind directions, and, thus, may measure the amount of dust that deposit during winds from a given source.

dk-TEKNIK ENERGY & ENVIRONMENT has in a series of projects used a newly developed wind directional sampler /27/, and this sampler is concluded to be suitable for the measurement of the total dust deposition from a given source. By means of a parallel measurement of the background level of dust deposition, the contribution from the source can be determined by correcting for the dust deposition caused by the background sources in that area. The background level can be measured by means of a bulk sampler in an area that is not affected by the source, i.e. normally at least 1000 metres from the source. The report describes examples where the wind directional sampler has been used to determine the contribution of dust deposition from stockpiles such as coal piles and gravel pits.

Regulation of fugitive dust emissions
The report describes the practice used in Denmark for regulation of fugitive dust emissions.

It is recommended that the terms of operation specified in environmental approvals generally follow the following principles:

• Requirements for equipment and machinery with a view to physical improvements, e.g. enclosure, wind shields, sprinkling, ventilation including cleaning of the exhaust air in cyclones and bag filters etc.
• Requirements for the performance of work, e.g. continuous watering of stockpiles and driving areas, cleaning and maintenance of equipment
• Requirements for instruction of employees
• Requirements for inspection and monitoring

The report gives a review of options for reducing fugitive emissions of dust by means of terms of operation, including transportation, driving on paved and unpaved areas, design and handling of stockpiles, use of conveyors and handling of materials, use of wind screens, minimization of dust emissions from stationary equipment and machinery, watering and use of suppressants to prevent dust from becoming airborne.

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