Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 1/24)
Character Range: 943233–946285

4                   Exposure assessment

4.1              Introduction
Exposure assessment involves the estimation of the magnitude, frequency, extent and duration of exposures to contaminants. In the data evaluation stage, the CSM is refined to produce an understanding of the source(s), pathway(s) and exposed population(s) that require assessment at Tier 2. In the exposure assessment stage, the CSM is used to generate a numerical representation of the exposure pathways that can be modelled quantitatively; these are the model input values. The input values are then used to model exposure point concentrations and estimate intakes of contaminants by the exposed populations.

To promote consistency and transparency in making exposure assessment assumptions, enHealth has established a framework for exposure assessment, set out in enHealth (2012a). This section follows the framework, adding details specific to contaminated land assessment.

Exposure assessment modelling methods have largely been developed for use in contaminated land risk assessment by the US EPA, and in the following section there are many references to US EPA guidance documents. These documents are extensive, well referenced and provide model algorithms and guidance on their use. Adoption of the modelling methodology in this Schedule does not imply endorsement of the US guidance; rather the US methods should be adapted to meet Australian policy objectives and environmental circumstances.

In the following sections, the derivation of model input values generally using point estimates (that is, single value estimates) is discussed. A more complete discussion of the use of probability distributions as input values (for example, the Monte Carlo method) is provided in Section 2.4.4. There may be circumstances where the use of probabilistic methods is appropriate in Tier 2 assessments, and it is not the intention of this Schedule to discourage the use of probabilistic models where their use can be beneficial to the outcome of the assessment.

The key stages of exposure assessment, as applied to contaminated land risk assessment, are to:
    1. determine input values for contaminant concentrations
    2. determine physicochemical properties of contaminants
    3. determine physical input values for pathways
    4. determine input values for exposed populations
    5. estimate exposure concentrations
    6. estimate chemical intake
    7. collect data to test predictions in stages 4 and 5 (where relevant).
Stages 1 to 4 comprise the translation of the CSM into modelling terms as described. Stages 5 and 6 are achieved using a quantitative health risk assessment model. Stage 7 is a test of the model.

4.2              Exposure settings

    4.2.1          Defining model inputs to represent the contaminant source
The data evaluation stage should provide a good understanding of the source. Consideration needs to be given as to how the contaminant concentration will be applied in a Tier 2 human health risk assessment; that is, what values will be