Factors Affecting Indoor Air Concentrations of Volatile Organic Compounds at a Site of Subsurface Gasoline Contamination

• Published in: Environmental science & technology Vol. 30; no. 10
• Main Authors: Fischer, M.L., Bentley, A.J., Dunkin, K.A., Hodgson, A.T., Nazaroff, W.W., Sextro, R.G., Daisey, J.M.
• Format: Journal Article
• Language: English
• Published: United States 01.11.1995
• Subjects: 54; AIR; CONTAMINATION; DILUTION; GASOLINE; INDOORS; ORGANIC COMPOUNDS; SOILS; TRANSPORT; VENTILATION; VOLATILE MATTER
• ISSN: 0013-936X; 1520-5851

We report a field study of soil gas transport of volatile organic compounds (VOCs) into a slab-on-grade building found at a site contaminated with gasoline. Although the high VOC concentrations (30-60 g m{sup -3}) measured in the soil gas at depths of 0.7 m below the building suggest a potential for high levels of indoor VOC, the measured indoor air concentrations were lower than those in the soil gas by approximately six orders of magnitude ({approx} 0.03 mg m{sup -3}). This large ratio is explained by (1) the expected dilution of soil gas entering the building via ambient building ventilation (a factor of {approx}1000), and (2) an unexpectedly sharp gradient in soil gas VOC concentration between the depths of 0.1 and 0.7 m (a factor of {approx}1000). Measurements of the soil physical and biological characteristics indicate that a partial physical barrier to vertical transport in combination with microbial degradation provides a likely explanation for this gradient. These factors are likely to be important to varying degrees at other sites.