Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p4
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 4/4)
Character Range: 894027–895570

contaminants and their likely mobility in the environment
    * the physical properties associated with the geology and hydrogeology underlying the site
    * the potential presence of subsurface geology or structures that may act as preferential pathways for vapour migration on and off the site
    * the people who may be exposed to the contaminants
    * the means by which exposure could occur and the frequency of exposure.
Additional information is presented in Schedule B2.

    1.4.3          The tiered approach
The human health risk assessment process for assessment of site contamination is generally undertaken in stages or 'tiers' involving progressively more detailed levels of data collection and analysis. In this guidance, the tiers are referred to as Tier 1, Tier 2 and Tier 3. The approach provides for assessment at a level of complexity that is appropriate for the problem under consideration; the degree of health protection achieved is equal at each tier. As the amount of data and assessment detail increases and the conceptual understanding of site conditions (that is, the CSM) is refined, the level of uncertainty decreases.

A risk assessment progresses from Tier 1 to Tier 2 when uncertainty and risks at Tier 1 may be unacceptable and further assessment is needed. Progression from Tier 2 to Tier 3 is similarly driven. Tier 3 provides more detailed and specific focus on risk-driving factors. It should be noted that the activities within the tiers may vary depending on the scale and complexity of the project.