McAlary, T.A., P. Dollar, P. de Haven, R. Moss, G. Wilkinson, J. Llewellyn, and D. Crump, 2002, "Assessment of Subsurface Vapor Transport Through Triassic Sandstone and Quarry Fill into Indoor Air in Weston Village," Runcorn Platform Presentation, Indoor Air 2002, Monterey, CA, July 1-5, 2002.
Subsurface vapour intrusion into indoor air by volatile organic compounds (VOCs) associated with contaminated land is a potential exposure pathway of increasing interest. This paper describes a comprehensive case study of this pathway, including: indoor air quality (IAQ) monitoring at 0.003 parts-per-billion (ppb) quantitation limit (QL), a detailed geologic characterization, extensive subsurface vapour sampling and analysis, pneumatic testing at the laboratory and field scales, building pressure and ventilation studies, a comprehensive statistical analysis of the vapour attenuation coefficient (“alpha factor”), and a comparison to the USEPA spreadsheet version Johnson and Ettinger (1991) model. The results show that the vapour concentrations in indoor air are dramatically influenced by the gas permeability and structure of the subsurface geologic materials. Properties built on the sandstone bedrock had IAQ that was barely distinguishable from outdoor air quality (OAQ); whereas, properties built on poorly consolidated quarry spoil backfill typically had IAQ 2 to 3 orders of magnitude more concentrated than OAQ.