Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:10:p6
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 10 (pt 6/7)
Character Range: 1136540–1139439

is not observed or expected to occur.
Tier 1 assessment is a risk-based analysis comparing site data with generic published screening criteria for various property uses (for example, residential, commercial and industrial). This tier has the lowest data requirement, generic exposure assumptions, and applies the most conservative criteria.
Tier 2 assessment is a site-specific assessment in which risks to potentially exposed populations are assessed using site-specific data on pathways, land uses and the characteristics of the exposed populations. A Tier 2 evaluation usually involves the use of a quantitative exposure model. A Tier 2 evaluation is more complex than a Tier 1 evaluation and requires more site-specific information. As a result, a health protective effect will be achieved with a lower level of conservatism.
Tier 3 assessment is a further step from a Tier 2 assessment and looks in more detail at specific risk-driving factors. This often involves additional data collection, and may incorporate more sophisticated modelling techniques.
Tolerable daily intake (TDI) is analogous to acceptable daily intake. The term 'tolerable' is used for substances that are not deliberately added, such as contaminants in food and water.
Toxicity is the inherent property of a chemical substance to cause an adverse biological effect.
Toxicity reference value (TRV) is a measure of tolerable intake or acceptable risk. The TRV may be associated with either a threshold (i.e. ADI, TDI, TC or reference dose) or non-threshold (i.e. slope factor or unit risk) dose-response relationship.
Uncertainty is a lack of, or incomplete, information or knowledge.
Unit risk is an expression of the incremental risk associated with increase in exposure by a single unit of exposure measure. It may also be expressed as the plausible upper bound estimate of the probability of a response from a chemical over a lifetime. It is derived from the slope of the linearised doseresponse relationship and usually expressed in units of concentration for a specified medium (e.g. incremental risk per μg/m3 in air).
Uptake is the amount of contaminant that enters the body through a barrier such as the skin, lungs or gut lining. Uptake is generally less than intake because not all the contaminant that enters the lungs or gut, or contacts the skin, is absorbed.
Vadose zone is the portion of the sub-surface between the water table and the ground surface, also termed the unsaturated zone. Soil pore space in the vadose zone is only partially occupied by water, which is held in place by capillary forces and adhesion to soil particles.
Variability describes true differences in attributes or values due to diversity or heterogeneity.
Vulnerability refers to human populations at higher risk due to environmental factors; examples of vulnerability factors include poverty, malnutrition, poor sanitation, climate