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Odour assessment
using odour source modelling
Updated February 2006
∗
EPA 373/06: This guideline provides criteria for the management of odour emissions,
particularly for new or expanding developments. It specifically addresses the use of
computer modelling and the determination of appropriate separation distances.
Introduction
The Environment Protection Authority (EPA) expects proponents of developments with odorous
emissions to include best practice odour management. Computer modelling is a useful tool in
assessing the potential odour impact of a proposed development.
Odour criteria in South Australia are based in principle on compliance with the general
environmental duty to avoid environmental nuisance using ‘best available technology economically
achievable’ (BATEA).
The modelling process should not be seen as a substitute for BATEA; best practice principles must
be applied regardless of the outcome of any modelling undertaken. Nor should modelling be the
only method used to assess the potential odour impacts of a development; other tools are:
• complaint history
• previous practical experience with the activity
• consultation outcomes
• community odour diaries and surveys
• assessment of emission control proposals.
To assist the planning process, these guidelines provide consistency in assessing a new
development. When an industry complies with the recommended separation distances, there are
generally few complaints under normal operating conditions, allowing for some plant upset and
equipment or power failure.
∗
Update primarily deals with interpretation of ‘population density’.
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Odour assessment using odour source modelling—February 2006
Modelling assessment should be undertaken by someone with the necessary experience and
appropriate training in the particular model used. More detailed information on the assessment of
odour is available in the references listed.
Legislation
The principal legislation dealing with odour in South Australia is the Environment Protection Act
1993 (the Act). In particular, section 25 imposes the general environmental duty on all persons
undertaking an activity that may emit odour to take all reasonable and practicable measures to
prevent or minimise any resulting environmental harm. In addition, causing an odour may
constitute environmental nuisance, an offence under section 82 of the Act.
Consultation
This guideline was prepared by the EPA with the cooperation of Business SA, the Engineering
Employers Association (SA), the Foundry Council, and a selection of licensees under the Act who
employ processes with the potential to produce odour.
Application of this guide to new or expanding developments
When assessing proposals that may have unacceptable odour impacts at odour sensitive premises,
the EPA will consider the following:
Best available technology economically achievable (BATEA)
If odour impacts associated with the development of a new industrial facility (taken in the widest
possible sense) are likely, the new facility should be designed using best practicable engineering
design, and operated using best practice management systems.
Odour minimisation
The general environmental duty referred to above means that, when preparing the proposal, the
proponents should consider alternative sites, technologies or management systems that may
reduce or eliminate odour impacts on sensitive land uses.
Public expectation
The community expects levels of odour to meet, or better, accepted community standards or
criteria (as given by this guideline). As a regulator, the EPA needs to know:
• why the proposed site was chosen in favour of some alternative site
• what processes exist and why certain technologies were chosen
• what management procedures (including emergency procedures) are in place to minimise odour
emissions
• what impact odour emissions associated with the project will have on the amenity and health
of people in the area.
These issues need to be addressed in submissions to the EPA.
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Odour assessment using odour source modelling—February 2006
Management objectives
The overall objectives in the management of odorous industries or facilities are to:
• minimise odour emissions and their impacts
• ensure that the proposed industry or facility does not expose neighbouring land users to an
unacceptable level of odorous emission
• ensure that the industry continues to operate in such a manner that the odour emissions are
managed within the accepted criteria
• apply principles of ongoing risk evaluation and management, given the evolving understanding
of odours and their potential health effects.
Odour assessment of new industry and facilities
If the EPA believes that a project involves a significant probability of odour impacts, it will require
a quantitative odour assessment at an early stage of the assessment process. The need for such an
assessment will be determined on a case-by-case basis and will depend on the nature of the
project and the sensitivity of the surrounding land use.
As the scope and extent of the odour assessment will vary from project to project, the EPA will
provide specific advice to each proponent. In general, the EPA requires that an odour assessment
be carried out as outlined within this guide, undertaken and certified to the EPA’s satisfaction by a
competent and reputable analyst accepted by the EPA, at the proponent’s expense. This process
requires the analyst to satisfy the EPA that the assessment was done objectively and
independently.
In conjunction with the quantitative odour assessment, the EPA expects the proponent, as part of
an environmental management plan, to recognise and address the public’s perceptions and
concerns about the emitted odours. Community consultation in the decision-making process is
important in the management of odour.
Odour measurement
Unfortunately, there are no instrument-based methods that can measure an odour response in the
same way as the human nose. Dynamic olfactometry, as it is known, is the basis of odour
management and is the method approved by the EPA. Dynamic olfactometry is the measurement of
odour by presenting a sample of odorous air to an independent panel, in a range of dilutions, and
seeking responses from the panellists on whether they can detect the odour. The correlations
between the known dilution ratios and the panellists’ responses are then used to calculate the
number of dilutions of the original sample required to achieve the odour threshold. The units for
odour measurement using dynamic olfactometry are ‘odour units’ (OU), which are dimensionless
and are effectively ‘dilutions to threshold’.
The EPA has updated its criteria for odour measurement to the Australian Standard Stationary
Source Emissions—Determination of odour concentration by dynamic olfactometry, AS4323.3:2001,
Standards Australia.
Odour guidelines
Odour complaints occur when individuals consider the odour to be unacceptable and are
sufficiently annoyed by it to take action. As well as an individual’s sensitivity, there are five
factors that influence odour complaints:
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Odour assessment using odour source modelling—February 2006
• frequency of occurrence
• intensity
• duration of exposure
• offensiveness
• location of the odour.
The offensiveness of an odour is very subjective and relates closely to an odour’s hedonic tone—
the degree to which an odour is perceived as pleasant or unpleasant. Such perceptions differ
widely from person to person, and are strongly influenced by previous experience and by emotions
at the time of odour perception.
Odour offensiveness is also related to its character—what the odour smells like. Character allows
one to distinguish between different odours; for example, ammonia gas has a pungent and
irritating smell. The character of an odour may also change with dilution. For these reasons, odour
offensiveness is difficult to quantify; however, the other four factors are quantifiable and can be
built into a regulatory guideline.
Once the data for estimated odour emissions is available for the proposal, dispersion modelling can
be used to predict the area likely to be affected by the odour. There are many dispersion models
available that can predict odour impacts, of which ‘Ausplume’ is generally favoured for regulatory
use. When matched to a post-processor program, Ausplume can provide graphical representations
that are useful in illustrating the impacts associated with a given project.
Ausplume may not be suitable for dispersion modelling in cases where complex terrain may cause
wind channelling, or where slope flows, recirculation or sea breezes may affect dispersion. In
these cases, other models such as the diagnostic model ‘Calpuff’ and prognostic model ‘TAPM’ may
help in making a valid assessment of likely odour dispersion.
The perception of the human nose typically occurs over a time scale of seconds. Ausplume
typically models a one-hour period with adjustments for three minutes. To estimate the effects of
fluctuations in concentrations perceived by the human nose, it is possible to multiply model
predictions by a conversion factor called the ‘peak-to-mean ratio’. This process is discussed in the
NSW draft Odour Policy, with further reference to the scientific work performed to validate the
approach.
Odour emissions
The units of odour measurement, as determined by the Australian standard, are to be used for the
estimates of odour levels. The odour levels must represent full production under normal operation
as well as increased odour emissions from abnormal operation. An estimate of background odour
concentrations may also be required. Industries can have periods of higher emissions due to
maintenance, cleaning, equipment failure, abnormal events and outages. It may be appropriate to
use the higher emission levels to give greater protection from odour nuisance at surrounding
sensitive receptors.
The model and input data
The model to be used generally is Ausplume version 5. Normally at least 12 months of
representative hourly meteorological data is needed. Variation from this minimum shall be
permitted only with the agreement of the EPA.
While the EPA has some meteorological data sets in the Ausplume format that may be suitable,
major developments may need to acquire their own on-site meteorological data over a
representative time period to use in the modelling program. Other factors representative of the
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Odour assessment using odour source modelling—February 2006
surrounding site and associated topography are needed for modelling dispersion of the odour. In
complex terrain that may cause wind channeling, and where slope flows, recirculation or sea
breezes could affect dispersion, other models may be required. It may also be necessary to
consider the peak-to-mean ratios.
Odour criteria
Odour criteria are population dependent—as the population density increases, the increased
possibility of sensitive individuals raises the potential for odour complaints, and more stringent
criteria are necessary. The predicted odour levels (three-minute means) must not exceed the
following odour levels 99.9% of the time at sensitive receptors, not including houses on the
property of the development (see table).
Number of people
Odour units
(3-minute average, 99.9%)
2000 or more
2
350 or more
4
60 or more
6
12 or more
8
Single residence (less than 12)
10
In making an odour assessment, the number of people in a defined area or cluster must be
determined. Differing situations may require the use of more than one criterion so good judgement
may be needed to determine the best criteria to use. For an area or cluster, the potential growth
of the area and the boundaries of the associated zones as detailed in the appropriate development
plans must be considered. Where sensitive receptors exist, adjacent to each other, over a series of
planning zones, they would normally be considered as one single area for the purpose of this
guideline.
Some examples:
• If an odour source is in an area with a rural residence to the north and a town of 500 people to
the south, then the appropriate criterion is 10 odour units for the single residence and 4 odour
units for the town and adjoining houses.
• If a rural odour source has 4 individual houses nearby, one in each direction, then the
appropriate criterion is 10 odour units at each house as they are each considered single
residences.
• If a cluster of houses with a population of 70 people is near an odour source, the appropriate
criterion is 6 odour units. If there is a discreet zone of 2000 or more people, the appropriate
criterion is 2 odour units. If there is a single residence at the edge of the zone, the appropriate
criterion for this house is also 2 odour units.
Accurate odour modelling is highly dependent on the quality of the meteorological and emission
data used. Consequently, it is strongly advised that proponents of any new development use the
best data available, and allow substantial margin for error in their odour modelling.
As a general guide, if the predicted odour levels illustrated in the modelling are half the
acceptable level published in this guide, then the proponent can reasonably expect that the final
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Odour assessment using odour source modelling—February 2006
development will remain within acceptable odour levels in most circumstances. If the predicted
odour levels illustrated in the modelling are double the acceptable levels in this guide, then the
whole concept of the development would probably need to be re-examined. Predicted odour levels
between half and double the published acceptable levels would warrant a general re-examination
of the proposed odour control systems and of the modelling itself.
Draft separation distance guidelines under development
The EPA has issued a consultation Draft Guidelines for Separation Distances
1
, August 2000. This
document defines and recommends separation distances for a range of industries. Generally, the
distances do not depend on the size or throughput of the industry but are based on experience
with typical sized facilities using current best available technology, including odour control
equipment.
The separation distances would help protect nearby sensitive receptors from a range of air quality
issues, including odour, but are not designed as a substitute for good odour control using BATEA
principles. There may still be a requirement to use modelling as a tool to assess the potential
odour impacts, particularly if there are site-specific circumstances (local topography, sensitivity of
the receiving environment, size of proposed operation).
For some industries, such as piggeries and cattle feedlots, there are no defined separation
distances, but there are industry-specific guidelines developed to address the range of sizes in
feedlots and the management techniques likely to be in use.
Presentation of results
In presenting odour source modelling, sufficient information must be provided to allow a full
understanding of the results and how they were derived. Reference should be made to the EPA
Guideline Air pollution modelling—presentation of results (EPA 578/05, February 2005).
Further reading
• CSIRO Marine & Atmosphere Research 2005, TAPM; <www.dar.csiro.au/res/aq/tapm>
• Earth Tech Atmospheric Studies Group, Calpuff; <www.src.com/calpuff/calpuff1.htm>
• NSW EPA 2001, Draft policy: Assessment and management of odour from stationary sources in
NSW; <www.epa.nsw.gov.au/air/odour.htm>
• NZ Ministry for the Environment 2003, Good Practice Guide for Assessing and Managing Odour
in New Zealand; <www.mfe.govt.nz/publications/air/odour-guidelines-jun03/index.html>
• SA Environment Protection Authority 2000, Draft Guidelines for Separation Distances;
<www.epa.sa.gov.au/pub.html>
• SA Environment Protection Authority 2005, EPA Guideline Air pollution modelling—presentation
of results (EPA 578/05); <www.epa.sa.gov.au/pub.html>
1
<www.epa.sa.gov.au/pub.html>
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Odour assessment using odour source modelling—February 2006
Currency of these guidelines
These guidelines offer advice to assist with compliance with the general environmental duty and
specific environmental policies. They are subject to amendment and persons relying on the
information should check with the EPA to ensure that it is current at any given time.