Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 3/4)
Character Range: 891371–894306

health screening levels (HSLs) are defined as 'the concentration of a contaminant above which further appropriate investigation and evaluation will be required'. They are defined for specific land uses and will not necessarily be protective for other land uses. There are a number of assumptions (for example, relating to site geology or the nature of exposure) built into the HILs and HSLs, and careful review should be undertaken to determine whether these assumptions are applicable on a given site. The absence of an HIL for a specific contaminant does not indicate that no potential risk is posed; rather that a site-specific risk assessment may be required.

The HILs are presented in Schedule B7. HSLs have been developed separately by CRC CARE (Friebel & Nadebaum 2011) and may be adopted where applicable (for further information refer to Schedule B1). Levels marginally in excess of the HILs and HSLs (where applicable) do not imply unacceptability or that a health risk is likely to be present. Similarly, levels less than the HILs may not imply acceptability or that a health risk does not exist for a sensitive sub-population (for example, people with pre-existing illness and people with pica (relatively common in some groups with severe or profound intellectual disability)). These issues would need to be addressed in site-specific assessment. Subject to an appropriate investigation and assessment process, a decision not to take further action or to take further action may be justifiable.

HILs and HSLs (where applicable) are not intended to be clean-up levels. The decision on whether clean-up is required and if so, to what extent, should be based on site-specific assessment. Health risk assessment is one aspect of making such a decision though other considerations such as practicality, timescale, effectiveness, cost and durability are also important.

    1.4.2          Conceptual site model
A conceptual site model (CSM) is a representation of site-related information regarding contaminant sources, receptors and the exposure pathways between those sources and receptors. The development of a CSM is an essential part of all site assessments and provides the framework for identifying how the site became contaminated and how potential receptors may be exposed to contamination either in the present or in the future.

In order to commence a risk assessment, it is necessary to develop a preliminary CSM. Factors to be considered include:
    * the typical and maximum concentrations of contaminants on-site
    * the vertical and horizontal distribution of the contaminants
    * the physical and chemical properties of the 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