Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p6
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 6/9)
Character Range: 934227–937147

such as a layer of imported fill material, or a layer of clay that preferentially adsorbs a contaminant. If the distribution or depth of the contamination is not characterised correctly, the risk can be overestimated or underestimated. The risk of exposure to contaminant vapours derived from soil or groundwater contamination is often driven by the soil type and porosity, the depth of the contamination and the presence of organic carbon in the soil profile. Therefore, by understanding which soil stratum is impacted, key parameters such as soil type, soil depth and Foc can be obtained from the appropriate zone, and a more accurate assessment of the risk can be made.

    3.4.3          Refining the exposure pathways
Site investigation data may either introduce or rule out exposure pathways in the CSM. For example, establishing the groundwater flow direction with improved certainty might show that a pathway to a potentially exposed population does not exist because that exposed population proves to be located upgradient of the source. Detailed guidance is available in Schedule B2.

Guidance on physical hazards such as inhalation of asbestos fibres, risk of fire or explosion from flammable gases and risk of exposure to asphyxiating atmospheres (for example, methane, carbon dioxide, carbon monoxide) is beyond the scope of this Schedule. Guidance on the assessment of asbestos is provided in Schedules B1 and B2. Appropriate guidance should be followed for the assessment of physical hazards.

Exposure pathway assessment should lead to a clear conclusion on which pathways are considered viable and which are not, with reasoning and appropriate evidence. Where viable pathways cannot be assessed in the risk assessment process, appropriate controls for mitigating the risk should be provided and documented.

    3.4.4          Tier 1 screening
Tier 1 screening involves comparison of site analytical results with appropriate screening criteria. In Australia, appropriate HILs (including interim HILs for vapour and, where applicable, HSLs for petroleum hydrocarbons and assessment criteria for asbestos) and GILs are used for Tier 1 screening to provide a rapid assessment of whether the site contamination may be of concern with respect to human health. Should contaminant concentrations at a site occur at levels that are below the Tier 1 levels, this implies that for the majority of the people in the population there is no significant health risk from contamination and that remedial action may not be required to protect human health.

For contaminants where HILs are not available, the methodology set out in Schedule B7 could be adopted to derive HIL-equivalent screening criteria. Sources of toxicity reference values should be considered in the same way as has been done for those chemicals with HILs (same hierarchy and other considerations). Exposure scenarios should be used as laid out in