Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:2:p7
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 2 (pt 7/9)
Character Range: 912627–915691

Tier 2 criteria are exceeded, but further assessment (or action) is not proposed, the information and logic used to inform the decision should be documented clearly and transparently.

     2.4.1.3         Tier 3
A Tier 3 assessment may be required where exceedence of Tier 2 site-specific risk-based criteria is judged to represent a potentially unacceptable risk to human health. The Tier 3 assessment typically focuses on the risk-driving contaminants in more detail, although studies aimed at reducing the uncertainties inherent in the modelling of exposure pathways are also common at Tier 3. This level of assessment may include statistical methods and mathematical modelling to assess the significance of the site contamination. The collection of additional data, such as soil vapour sampling, ambient air sampling, analysis of dust, biological monitoring and additional site investigations may be needed to support Tier 3 assessments in order to reduce uncertainties.

The tiered approach should provide a process for addressing site contamination methodically, with the level of complexity and cost proportional to the significance of the risk. Increased levels of site-specific data reduce uncertainties inherent in the assessment. It is important to note that for a given site the level of protection of exposed populations should remain the same regardless of the tier of assessment conducted.

    2.4.2          General risk assessment assumptions
Risk assessment is a tool to help risk managers make decisions about contaminated sites. Risk assessment should incorporate an appropriate level of health protection such that sensitive exposed populations are adequately protected. Because of the many uncertainties inherent in risk assessment, it is desirable that quantitative risk assessment methods should overestimate risk to some extent.

Risk assessors should transparently describe the assumptions and uncertainties involved in a risk assessment.

Risk assessors should select exposure model inputs carefully, and consider the reasonableness of the exposure settings when taken together. Some examples of how assumptions may be applied to a model are:
    * using an average (where there is sufficient data and it is relevant to the exposure being assessed) and high-end estimate (e.g. upper 95th percentile or maximum where relevant) of the contaminant concentrations to represent the source
    * choosing an appropriate sensitive exposed population for the CSM, such as young children or pregnant women
    * assuming that the behaviour of the sensitive population results in plausible high-end exposures (e.g. long exposure periods, exposure of large areas of the body, high activity rates)
    * assuming that exposure to the population may occur by several pathways (e.g. a child who plays in contaminated soil also eats vegetables grown in this soil)
    * using fate and transport models (e.g. for vapour intrusion pathways) which provide estimates of the amount of contamination that reaches the exposed populations.
Models should only