Adsorption of volatile organic chemicals (VOC's) directly onto the soil minerals at low soilwater contents is an important process. The direct adsorption of VOC vapors can increase the total adsorption capacity of the soil by several orders of magnitude. Vapor sorption can therefore cause high VOC fluxes out of the soil during periods with increasing soil-water contents. Models for predicting VOC sorption, including vapor sorption, as a function of water content and other soil properties are therefore valuable, for example for evaluating VOC volatilization and exposure risk at polluted soil sites. A new model for estimating trichloroethylene (TCE) sorption from BET-N₂ soil surface area and from soil clay content was developed based on TCE sorption data from 22 different porous media. The new TCE sorption model was tested against independent TCE sorption data for two Japanese soils (a sand and a clay loam). The data were measured by a recently developed gas chromatography micro-column (GCMC) method. The VOC sorption model well predicted TCE retardation (sorption) as a function of soil-water content. The new VOC sorption model can be useful, for example when designing soil vapor extraction systems that are used for clean-up of VOC polluted soil sites.

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