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

2.5.4 Airborne Respirable Dust Levels

It is anticipated that this pathway of exposure will generally be insignificant relative to direct ingestion of soil and water, and to dermal absorption. However, exposures corresponding to this pathway should be calculated if deemed appropriate by the assessor. When included, the concentration of a specific contaminant in the respirable airborne dust should be assumed to be equal to the concentration in surface soil (maximum or average, as appropriate).

When this pathway is included, an average airborne concentration of respirable ( 10 µm aerodynamic diameter) particulate matter should be assumed to be 0.76 µg/m³ (based on U.S. EPA, 1992). For situations where significant vehicle traffic on contaminated unpaved surfaces is a concern, such traffic can generate considerably greater suspended dust levels. Dust levels from unpaved roads vary according to climatic conditions, traffic levels, and the texture and nature of the road surface material (Claiborn et al., 1995). A reasonable dust level created by vehicle traffic on unpaved roads is 250 µg/m³ (down-wind side of the road; Claiborn et al., 1995).

2.5.5 Models

Models may be necessary to estimate the concentrations of contaminants of potential concern in groundwater, surface water, indoor or ambient air, produce and vegetation, fish, wild game or other environmental media through which receptors may potentially be exposed. Necessary modelling should be kept to a level of complexity consistent with the "screening" nature of the risk assessment. Estimates of the concentrations of volatile COPCs in indoor air should be derived from the methods presented by Williams et al. (1996) and the CCME (1996 - Appendix G). Likewise, estimating COPC concentrations in groundwater and in surface water may be obtained from the methods described by the CCME (1996). For estimating COPC concentrations in vegetation, methods presented by the CCME (1996 - produce check) or the Oak Ridge National Laboratory (ORNL) (1998) may be used. For estimating COPC concentrations in fish and wildlife, simple bioaccumulation/biomagnification factors may be employed where available on a chemical-by-chemical basis, or more sophisticated modelling may be used, as deemed appropriate by the risk assessor.

Not withstanding the guidance above, other modelling methods may be used as long as they are generally accepted. Any models employed should be fully referenced to permit peer review, including a rationale for the specific model selected.