Obtaining quantitative vapor emissions estimates of polychlorinated biphenyls and other semivolatile organic compounds from contaminated sites

Soils contaminated with polychlorinated biphenyls (PCBs) and other semivolatile organic compounds (SVOs) represent a potentially major, ongoing source of these compounds to the environment, especially during warmer temperatures. A great deal of work has been devoted to understanding the mechanisms that govern the vaporization of SVOCs from soil, but to date, few quantitative estimates have been published regarding emissions from contaminated sites. The present paper describes methods for obtaining quantitative estimates of SVOCs from soils based on flux chamber measurements, modeling, and ambient air measurements. On wet (i.e., H2O) soils, SVOCs at very low chemical loading levels on the adsorption sites (the so-called critical chemical concentration, critical loading, or saturation concentration) will behave, for volatilization purposes, as the pure-liquid substance would. For one soil, the PCB critical concentration was determined to be 775 ppm (95% confidence interval, 5.40E+02). Flux chamber-measured emissions from two contaminated sites were used and compared to model estimated values. The results agree reasonably well and indicate that the modeling approach used provided a conservative upper bound on the emissions. These approaches can be used to develop emissions estimates for SVOC-contaminated sites and inputs to air dispersion models.