Contaminant Transport in the Soil Matrix
Research Team: Yoram Cohen (PI), Jordi Grifoll (Research Scholar), Robert van de Water
(Graduate Student).
This project focuses on the development of a theoretical model for the transport of chemical
contaminants in the unsaturated soil matrix under the action of rainfall, soil drying, and diurnal
temperature cycling. In the first phase of the project a theoretical analysis which allows the
determination of the significance of a multiphase versus a pseudo-single phase transport analysis of
chemical transport was developed. A multiphase soil transport (MST) model was developed to
investigate the movement of organic chemicals in the soil vadose zone. The MST model incorporates
a soil moisture transport model coupled with a mass transfer model. In the MST approach
climatological rainfall and soil drying data for the location of interest are used for the desired
simulation period. In the first phase of the study it was found that, for the Los Angeles area,
contaminant flux predictions that incorporates the effect of rainfall vary significantly throughout the
year (by up to two orders of magnitude). The rate of volatilization was also found to be a function
of the period during which the chemical is introduced to the soil matrix, a phenomenon which is
linked to the yearly distribution of rainfall. For example, benzene which is introduced into the soil
matrix in January is expected to volatilize from the soil at a rate lower by about a factor of three
relative to benzene which is introduced into the soil in July.