Offsite Dust Emissions – How to Model Dust Settling Rates

Case Study

Dust exposure of neighbouring residents to grain handling facility.

Victorian residents located within close proximity to a grain handling facility were exposed to dust associated with the operation of the facility including from the many trucks delivering to the site.    After years of complaining to the EPA legal action was initiated against the grain handling facility owner based upon environmental monitoring undertaken by independent monitoring services provider.

The lawyers acting on behalf of the complainants and having been advised by the EPA and a private provider of environmental monitoring services had already commissioned some environmental monitoring base upon a SEPP with a benchmark of 4 g/m2/month above which dust levels were deemed to be an unacceptable nuisance by the time Envirosaphe was involved.    The brief was to develop methods to be able to a mathematical method using existing and future data to be able to determine the likely past exposure levels experienced on the site.

Key issues.

  1. Only SEPP used as basis to assess performance of Grain handling facility is one applicable to quarries and mining.
  2. Based on the SEPP grain handling facility owner not required to commission any modelling of off-site dust exposure or atmospheric monitoring to determine whether acceptable emissions of dust were occurring because of the annual tonnages involved did not meet a threshold even though the rate over a harvest period was high, if applied over a year would require such an assessment.
  3. The implementation of the SEPP deemed by the EPA to apply in the situation of off-site impacts of grain handling operations applies to new, not existing facilities even if existing facilities significantly increased the quantities handled on site.
  4. EPA role in situation of people affected by emissions making a complaint is weighted towards the enterprise generating the emissions being able to continue with minimum restrictions.   Jobs (employment) have a priority over protecting environment of neighbours.
  5. After complaints from local residents the EPA required action of grain handling facility owner to undertake measures to reduce dust generated on site, but there was no requirement for the grain handling facility to demonstrate compliance to any benchmark.   No testing. Not required by SEPP or EPA.   Testing has to be done at complainant’s expense.
  6. Difficulty for anyone adversely affected by emissions to demonstrate any injury from the emissions or unacceptable dust emissions.
  7. Difficulty of determining practical but appropriate monitoring methods, location of monitoring to assess off-site impacts in order to demonstrate nuisance or health impacts by monitoring for dust deposition rates.   Physical limitations of site, proximity to roads.
  8. Inability of endorsed atmospheric emission modelling methods to determine likely off-site dust exposures given they are based upon fixed point emissions and gas behaviour, not multi-point multi-parameter dust emissions with diffuse variable location emissions.   While complex and comprehensive they answer a different question to that of a real world question such as, what levels of environmental contaminants will be experienced off-site at a particular location.
  9. Appropriate modelling methods to determine likely past exposures to dust using atmospheric monitoring and bureau of meteorology data combined with daily truck delivery data and individual truck loads to extrapolate to generate minimum likely and average likely dust deposition rates.

The Model

The Model was based on the understanding that the cumulative dust deposited in excess over background dust depositions over a 30 day period would be the sum of each individual truck delivery and the conditions existing when that delivery was made over that period.

The developed Model was based upon the following formula.

 

 

 

 

M is the dust level above the background dust level over a 30 day period.

N is the number of trucks per day.

W is the wind direction averaged over each working day.

T relates to the types of trucks.

D is the tonnage of grain transported,

S is the effectiveness of dust suppression.

The model is based upon the following understandings and assumptions.

M is the dust level above the background dust level over a 30 day period.

N is the number of trucks per day.

W is the wind direction averaged over each working day.

T relates to the types of trucks.

D is the tonnage of grain transported,

S is the effectiveness of dust suppression.

Existing modelling employed by most consultants and recommended by the EPA do not address the issue of dust settling rates which are cited by the EPA as a way of evaluating dust generation and its impact off site.   Normal modelling is based upon airborne concentrations of contaminants including dusts but there is no simple relationship between the dust settling rates over a given area (units gm/m2) and the average airborne concentrations expressed as milligrammes per cubic metre.   That would mean that no way could be developed to link any monitoring results to the existing modelling methods recommended.   A new approach had to be developed especially if the question asked of the researcher related to previous years of deliveries to the site and the likely off-site effects.

The result of the work was that the independent air sampling company the results which found excessive dust settling levels generated in the 2013/2014 harvest period when dust suppression measures were being implemented.   The modelling did suggest that dust levels prior to dust suppressions would have been higher for a significant number of harvest periods on previous years based upon truck movement data and wind direction and speed data from the Bureau of Meteorology from a weather station closely located to the site in question.    The matter was settled not tested in the courts but an out of court agreement with damages was negotiated.

If you are interested in further information on this investigation please contact Michael Beale at EnvirosapHe.

Note:  Envirosaphe is said as envirosafe.

 

 

 

Posted in Dust Emissions