Protocol for the Derivation of Environmental and Human ... - CCME

Appendix G
Appendix G
Development of a Relationship to Describe Migration of
Contaminated Vapours into Buildings
1.0 Introduction
A study (OAEI 1994) leading to the development of a relationship to describe the migration of
contaminant vapours into buildings was commissioned by Health Canada. The objective of the study
was to develop a simplified relationship between subsurface contaminant concentrations and indoor air
concentrations, arising from the migration of contaminant vapours into buildings. The purpose of the
relationship is to assess, at a screening level, the relative significance of vapour transport and inhalation
as an exposure scenario in the context of the establishment of soil quality guidelines. The results of the
study are presented here.
2.0 Background
2.1 General
Health risk assessment has been used increasingly in the last few years to develop soil and groundwater
remediation guidelines, both on a site-specific basis and as regulatory guidelines. The risk assessment
procedure normally involves four main steps: hazard identification; toxicity assessment; exposure
assessment; and risk characterization. Exposure assessment is the process of determining the point-ofexposure
contaminant concentrations as a function of source concentrations for the relevant exposure
pathways, to estimate intake. The exposure pathways commonly considered include:
• ingestion of groundwater;
• ingestion of soil;
• dermal contact with soil and water;
• inhalation and incidental ingestion of airborne particulates;
• inhalation of vapours from soil and groundwater.
For volatile organic compounds, inhalation of vapours is often a dominant exposure pathway. In spite
of this, the risk-based guidelines that have been developed by regulatory agencies to date are often
based only on the direct pathways of ingestion, dermal contact, and intake of particulates. The Alberta
MUST (Management of Underground Storage Tanks) guidelines, which prescribe guidelines specifically
for petroleum contaminated soil and groundwater, are based primarily on exposure via vapour inhalation
(Alberta Environment, 1991; 1994).
The purpose of the present study is to develop a screening tool that will facilitate the identification of
situations in which the inhalation of vapours originating in contaminated soil and groundwater is a
significant pathway.
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