Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p5
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 5/24)
Character Range: 954083–957223

to real people should be selected for modelling.
    * Consistency— Schedule B7 provides behavioural and exposure duration assumptions for four standard exposure scenarios. Where site-specific assessments are essentially considering the same exposed populations in similar circumstances to the standard scenarios, the Schedule B7 behavioural assumptions should be adopted. This promotes consistency between site-specific risk assessments. Where the exposed population differs from the standard scenarios, amendments to behavioural assumptions can be made and should be clearly justified. Note that amending the commercial/industrial and public open space scenarios may be a common requirement, since activities within these land uses are prone to be variable.
    * Exposure via food and drink—the standard scenarios described in Schedule B7 provide limited consideration of exposure via food and drink because most Australians do not source a significant proportion of their food or water from their own property. However these sources may need to be considered in a site-specific assessment.
    * Allocation of background exposure (where it may contribute towards exposure to threshold contaminants)—related to the above point is the extent to which the exposed population is exposed to the contaminants under consideration as part of their daily lives. As well as presence in food and drink, contaminants may be present in the air, in consumer products, in household goods and in building materials. It is therefore necessary to consider the extent to which the risk assessment will allow for this exposure. At a screening level, simple (but appropriately justified) assumptions may be adopted. In more detail, background exposure can be considered on a site-specific basis depending on the site location and land use, as well as considering the contaminants individually.
It is recommended that in designing the exposure assessment, worst-case scenarios (particularly those where many 'high-end' assumptions are compounded) should generally be avoided. The sensitivity and uncertainty of the assumptions adopted in the exposure assessment should be considered.

4.3              Exposure point concentrations
An exposure point concentration is the estimate of the concentration of the source contaminant in the medium that the population is exposed to, at the location where exposure is predicted to occur.

It is preferred that, where possible, exposure concentrations are derived from direct measurements in the relevant media (soil, bore water, indoor air, fruit and vegetables and eggs).

However, under some circumstances it is not practical to measure concentrations directly, and in these cases exposure point concentrations are typically estimated using computer models.

The most commonly used exposure point estimation methods are:
    * vapour intrusion modelling used to estimate vapour concentrations in ambient air from measured soil vapour, soil, groundwater and non-aqueous phase product data
    * particulate modelling used to estimate the concentrations of dust generated from surface soil
    * groundwater fate and