A Comparison of Various Vapour Models to Actual Indoor Air Results to Determine Which Model(s) Most Accurately Predict Indoor Air Contaminant Concentrations. A. Denning and G. Clyde, Jacques Whitford Environment Limited
The soil-to-indoor air pathway is an important pathway for consideration in risk assessments at hydrocarbon release sites. In this study, actual site petroleum hydrocarbon vapour data will be compared to various predictive vapour transport models to determine which models most accurately predict ambient air concentrations. The models that will be examined include both Johnson and Ettinger (1991) and the Risk-Based Corrective Action (RBCA) Toolkit spreadsheet model. The RBCA Toolkit is currently approved for use in Atlantic Canada by the provincial regulators, and the Johnson and Ettinger model is widely used elsewhere for modelling the soil to indoor air pathway. The case study is based on a commercial/industrial site in Nova Scotia, Canada, where a petroleum hydrocarbon oil spill occurred on-site in 1999. Gasoline, fuel oil and lube oil range hydrocarbons were identified beneath the on-site building, including elevated levels of BTEX and some free product. Subsurface soil hydrocarbon concentrations, contaminant vapours beneath the floor slab and contaminant vapours in the ambient indoor air have been measured at the site. Site data will thus be assessed using the predictive vapour models and then compared to the actual ambient air contaminant concentrations to determine which model (if any) most accurately reflects the actual site concentrations.
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