Variation in North American regulatory guidance for heavy metal surface soil contamination at commercial and industrial sites

The health implications and remediation obligations of contaminated soils are significant issues in many urban areas of North America. For commercial and industrial sites, health concerns impact brownfield redevelopment and the conversion of fallow private land into public resources. To help manage health risks, regulatory agencies provide guidance values to identify maximum acceptable levels of contamination. Currently, these guidance values differ by as much as 5 orders of magnitude for some metals. The variability in North American guidance for Cd, Cr, Cu, Ni, Pb, and Zn surface soil contamination at commercial and industrial sites is examined. Ordered column diagrams illustrate the magnitude and dispersion of guidance values. Statistical analysis is used to investigate the significance of variations. Results indicate that commercial and industrial site guidance is more variable than residential site guidance and that even when the values are treated as lognormal random variables, some appear to be "uncharacteristic" outliers. The most significant regional trends are differences between US and Canadian guidance, but individual jurisdiction differences dominate over regional trends. When current guidance values sets were used in Hazard Index analysis applied to 20 sample urban brownfield sites, the results varied by 2 orders of magnitude.