Chemicals found at a site must be screened against environmental guidelines. To do this screening, the chemical measurement is compared against the CCME Environmental Quality Guidelines for protection of human health should be used. Where CCME human health guidelines are not available, other human health-based guidelines from reliable sources may be used. One source is the U.S. Environmental Protection Agency’s (US EPA) preliminary remediation goals (PRGs). Another is US EPA risk based concentrations (RBCs). When compared against guidelines, Contaminants of Potential Concern (COPC) are identified.
Adjusting US EPA risk based concentrations
For non-carcinogens, PRG’s or RBC's may be adjusted to reflect 20% of the US EPA toxicological reference value (TRV). A TRV is the maximum safe dose a human can be exposed to each day over a life time (mg/kg body weight/day). 20% of the TRV is taken to allow for exposure from other media and pathways.
Screening when a guideline is not available
In the event that a contaminant has no corresponding health-based soil quality guideline, the contaminant should be included as a Chemical of Potential Concern (COPC) for further risk assessment, unless the measured concentrations are consistent with natural or background concentrations.
Before a site is considered contaminated, concentrations of contaminants at the site, particularly natural elements (e.g., metals), should also be compared to background soil and groundwater concentrations (and surface water concentrations, if relevant), if data are available. If it is found that concentrations of contaminants at the site are representative of background levels, then the site may not be contaminated even though measured concentrations are greater than the guidelines. A further discussion of background levels is provided in Appendix A (external link) of the PQRA guidance document (Health Canada 2004).