What is a
Why is it important?
What is risk management?
of risk assessment
What are RA tiers?
The main outcome of this step is to set the overall purpose and
objectives of the Risk Assessment and determine the likely data
requirements. This includes:
- Setting the boundaries of the Risk Assessment (what will and will
not be considered), and
- Identifying what information needs to be collected, analysed or
What are the objectives of the site ERA?
The objectives of the assessment will depend on the state of knowledge regarding the
- If no previous studies or sampling have been undertaken, the objectives may relate to
establishing whether contamination is present, at what concentrations and in what media.
- If there has been a previous study undertaken which shows that a contaminant is present
in soils at high concentrations on the site but does not show the extent of contamination,
the objectives of the investigation may be to determine the extent of on site
contamination and determine whether contamination has extended off site to surrounding
land, water courses or groundwater.
- If previous Level/s of ERA have been undertaken, the site investigation objectives may
focus on filling relevant information gaps.
The objectives of a Risk Assessment will also vary depending on the
nature of the site and the Tier at which the Risk Assessment is being
undertaken. For example, the objectives for a Tier 1 Assessment may be
simply to compare the concentration of a contaminant in a discharge at a
site with a corresponding aquatic guideline value that is protective of
all aquatic freshwater species if the Site Characterisation indicates that
a complete pathway is possible. If the concentration in the discharge is
below the guideline value, we could conclude that the risk to aquatic
fauna is minimal or acceptable.
As the Risk Assessment Tier becomes more sophisticated, the objectives
could refer to the review and establishment of ecotoxicological threshold
criteria for a specific receptor species through a specific pathway. For
example, the establishment of end points for reproductive dysfunction in a
species of gull that ingests a contaminant that bioaccumulates through its
When specifying objective, you may wish to consider defining your
information requirements. These may include planning for a preliminary or
comprehensive site investigation, reviewing appropriate guidelines and
establishing appropriate guideline values for Tier 1 assessment, or
establishing possible pathways, e.g. determining the depth to groundwater
or groundwater flow direction.
Other considerations include:
What will be the level of effort applied to this level of
site investigations? What are the logistical boundaries and constraints to this
It is prudent to take account of the practical considerations of the site investigation
to ensure that all parties are informed of the boundaries of the exercise. Whether the
constraints are related to financial, time or resourcing issues, they should be factored
into the design and methodology early in the process. It may also be apparent due to the
characteristics of the site (e.g. size, likelihood of contamination, priority, etc.) that
the level of effort assigned to the site investigation should be greater or lesser
relative to the effort assigned to other sites.
What are the spatial and temporal boundaries for this
Tier of RA?
You will need to determine the appropriate time scale and spatial scale over which this
investigation will be carried out. While a Tier 1 investigation may only require a
one-off sampling event of on-site soils, a Tier 3 investigation may require a
multiple-event sampling of benthic macroinvertebrates in the nearby stream covering each
of the four seasons of the year.
In most cases some general information about
the site should be available from the Initiation
stage. This should include current and past land uses, consent information,
and site records. Further information is generally necessary to undertake a full
site characterisation, including:
- land use and land-use history:
- identify existing and past land uses on site
- identify nearby existing and past land uses
- document any gaps in these records
- identify what chemicals or materials were used at the site (types,
quantities, processes, storage, and disposal).
- identify and document any incidents of chemical releases and
possible release mechanisms
- identify potential or possible contaminants of
- identify other contaminant sources (e.g. nearby factory, natural
contaminant source), and
- broadly define the surrounding environment and
- potential ecological values
- buildings or heritage sites
- sensitive land uses (e.g. school) or human receptors,
- cultural sites.
Using this information, you should draw preliminary conclusions on the
following key factors:
- contaminants of concern
- potential receptors, and
- main pathways (contaminants release, transport and fate mechanisms).
Any assumptions used in completing the site characterisation, and any
information gaps should be clearly documented.
An example checklist is provided to help you to undertake a
A completed example is also provided
for the XYZ Enterprises example
that shows how key
conclusions can be obtained from this information.
In order to clarify the potential problems and information gaps for the site, it may be
advisable to develop a conceptual model in the form of a flow diagram or site map.
A conceptual model is a representation, either written or illustrative, of the
predicted relationships between ecological values and contaminants. Examples of a
conceptual model diagram for XYZ
Enterprises is shown, but you may choose to undertake this process using a different
diagrammatic approach. Examples of other conceptual models are shown in USEPA 1998 Appendix C.
The construction of a simple site model is a useful tool to help
characterise a site. A large number of site
visualisation and characterisation models or software packages have
been developed in recent years. These models may assist you in fully
identifying the problem at the site of concern.