Density-driven flow of gas in the unsaturated zone due to the evaporation of volatile organic compounds

A theoretical investigation of factors affecting the gas phase transport of evaporating organic liquids in the unsaturated zone is presented. Estimates of density‐driven advective gas flow using a simple analytic expression indicate that significant advective gas flow will result from the evaporation of volatile liquids in soils having a high permeability. Numerical simulations using a two‐dimensional cylindrical geometry and including the effects of phase partitioning between the solid, gas, water, and organic liquid phases show that mass transfer due to density‐driven flow may dominate the gas phase transport of some organic chemical vapors in the unsaturated zone.