Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:8:p6
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 8 (pt 6/7)
Character Range: 3051774–3054725

upper bound (holding all other at their medians), and then computing the outcomes for each combination of values (US EPA 1992). It can be used to test the effects of both uncertainty and variability in input values.
Site means the parcel of land being assessed for contamination.
Site-specific target levels are risk-based concentration values derived using Tier 2 or Tier 3 exposure modelling. May be used as criteria for further assessment or as clean-up levels.
Source is the contaminant that is considered to represent a potential risk requiring assessment.
Subchronic exposure is contact between a chemical substance (agent) and a target of intermediate duration between acute and chronic. Different bodies vary on their definitions of the duration of 'subchronic' exposure, since it varies with species. US EPA uses up to 10% of an organism's lifetime; however, between 36 months is often used when discussing subchronic exposure to people.
Susceptibility refers to intrinsic biological factors that can increase the health risk of an individual at a given exposure level; examples of susceptibility factors include genetic factors, late-age and early-life, prior or existing disease.
Threshold is the dose or exposure concentration of a chemical substance below which a stated effect is not observed or expected to occur.
Tier 1 evaluation is a risk-based analysis comparing site data with generic published screening criteria for various land 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 evaluation 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 evaluation is a further step from a Tier 2 evaluation 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 or material 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 analysis is a methodology that takes into account domain