Federal Contaminated Site Risk Assessment In Canada Part I: Guidence on Human Health Preliminary Quantitive Risk Assessment (PQRA)

2.5 Exposure Assessment

This section should include all exposure equations, chemical-specific characteristics, any necessary assumptions, the concentration (maximum, arithmetic average) used to represent the concentrations of COPCs in applicable media (air, water, soil, vegetation, etc.), and identification of and the results from the application of any methods or models required to estimate concentrations in one environmental medium based on those in another medium. Models may include those that employ measured soil-borne concentrations to estimate concentrations in groundwater, in surface water, in indoor air (volatile contaminants only), in ambient air, in agricultural produce, in vegetation used as country foods, in wildlife or fish that serve as food, etc.

In some cases, assessors may believe that the assumptions and equations presented in this guidance document are inadequate or inappropriate for the site in question. In these cases, the assessor should discuss his/her concerns with the client department and, where deemed appropriate, alternate assumptions and/or equations may be employed. However, it is imperative that the PQRA report contain a clear description of the inadequacies of the guidance presented here as it relates to the issue at hand, and that a convincing rationale (with citations) to support the use of alternate methods or assumptions is provided. For these cases, exposures should be estimated using the prescribed methods and assumptions and employing the assessor's preferred approach so that the impact on risk estimates is obvious and transparent.

2.5.1 Characterization of Potential Receptors

The physical characteristics (required for exposure calculations) for a variety of common receptor groups are presented in Table 3. When considering exposure pathways and circumstances beyond those encompassed by the equations and assumptions outlined in this document, additional receptor characterization assumptions should be drawn from Richardson (1997), if available. Where Canadian data on required receptor characteristics have not been published, alternate sources such as the U.S. EPA Exposure Factors Manual (U.S. EPA, 1997) should be used. Where alternate data sources are consulted, they must be clearly cited and fully referenced.

A table of the specific values employed in the PQRA should be included in the report.