Assessing the significance of subsurface contaminant vapor migration to enclosed spaces: site-specific alternatives to generic estimates.

摘要

The move toward more structured risk-based corrective action approaches has led to an increased interest in better understanding vapour migration to enclosed spaces. The significance of this pathway is the subject of intense debate, with many believing that existing non-site-specific risk-based screening levels are too conservative. However, little data are available to justify alternate approaches, and so this pathway must be addressed further on a more site-specific basis at many sites. Options for addressing this pathway on a more site-specific basis are presented. These include a more refined use of the existing screening algorithms for layered geological settings, as well as the use of recently updated algorithms that consider biodegradation.Each option has associated with it site-specific data collection and interpretation requirements, and these can vary in complexity of analysis and intensity of data requirements. A vision for a much simpler pathway screening analysis is presented and accompanied by a discussion of the developments necessary to progress toward that goal. This improved approach would determine, based on site characteristics assessed during an initial site assessment (specifically moisture content or measured effective diffusion coefficient and source zone vapour concentration), whether the vapour intrusion pathway needs be addressed further at the site.