Mobility of Residual Phase Organics in the Vadose Zone

A model was developed to characterize the transport of volatile or-ganics in variably saturated media. Water phase flow and transport and density dependent gas phase flow and transport were simulated. First order rate expressions using overall rate transfer coefficients were employed to incorporate dissolution and volatilization of immobilized residual organic compounds. Partitioning of solute between the water and gas phases was represented by a similar rate expression based on Henry’s law. The role of the soil gas phase in increasing subsurface contamination from volatile organics, and in dissipating residual amounts of these compounds was illustrated.