Tier 2 - Risk Characterisation
At this tier, Risk Characterisation should involve at
least some quantification of the potential risk to receptors from the contaminant/s of
concern. You should relate the on-site contaminant concentrations to the
modified criteria and decide on the likelihood of an adverse effect
Depending on the level of data collection you have undertaken for the preceding tasks,
it may be appropriate to determine population-level responses by sensitive species.
Quotient or continuous exposure-response methods may be used to achieve this and a
discussion of the use of these and other methods are provided in the resources.
As with Tier 1, the same questions are asked regarding the
concentration of contaminants compared with the modified criteria
established. Also, you should critically assess the quality and
limitations of the supporting data and the appropriateness of the modified
Tier 3 - Risk Characterisation
A Tier 3 Risk Characterisation should involve modelling
of contaminants, exposure and toxicity to quantify and simulate current and future risks to
populations, communities and/or ecosystems from contaminants. This may also include
estimates of effects associated with a range of control options from no mitigation (i.e. no action) to maximum
control (e.g. complete clean up).
A discussion of the use of these and other methods are provided in the
You may choose to relate the on-site contaminant levels to the criteria modified from
the Tier 2 RA and decide on the likelihood of an adverse effect being generated, while
taking into account the assumptions on which the criteria were derived and the background
concentrations of contaminants.
Again, a full assessment
of the assumptions used in modelling exposure and developing modified
acceptance criteria should be undertaken.