FACTORS AFFECTING INDOOR AIR CONCENTRATIONS OF VOLATILE ORGANIC-COMPOUNDS AT A SITE OF SUBSURFACE GASOLINE CONTAMINATION

We report a field study of soil-gas transport of volatile organic comp ounds (VOCs) into a building at a site contaminated with gasoline. Hig h VOC concentrations (30-60 g m(-3)) were measured in soil gas 0.7 m b elow the building. Measured indoor air concentrations were similar to 10(6) lower due to a sharp gradient in soil-gas VOC concentrations bet ween 0.1 and 0.7 m (a factor of similar to 10(3)) and the dilution of soil gas entering the building by wind-driven building ventilation (a factor of similar to 10(3)), Measurements of soil physical and biologi cal characteristics indicate that a partial physical barrier to vertic al transport in combination with microbial degradation can explain the gradient. While these factors are likely to be important to varying d egrees at other sites contaminated with VOC, we conclude that (1) the results of this study cannot be directly applied to estimate indoor ai r quality at other sites without the risk of incurring significant err ors and instead that (2) future attempts to estimate VOC transport int o buildings should be made with careful attention to the identificatio n and separation of physical and biotic effects.