ADVECTIVE-DISPERSIVE TRANSPORT OF DENSE ORGANIC VAPORS IN THE UNSATURATED ZONE .2. SENSITIVITY ANALYSIS

In the migration of dense organic vapors in the unsaturated zone, advection due to density gradients can play an important or even dominant role under certain conditions. Advective transport can distribute contaminants over a wide area within the unsaturated zone, thus increasing the potential for groundwater contamination. The controls on gas phase advective‐dispersive transport from a residual source of a generic organic compound are investigated using a numerical model. A sensitivity analysis reveals that, for compounds with high vapor pressures and molecular weights, in high permeability environments (coarse sands or gravels), the mass transported by density‐dependent advection may greatly exceed that transported by diffusion alone. If density‐dependent advection is the dominant transport mechanism, the extent of the contaminated area is increased if the ground surface is open to the atmosphere, rather than covered. The opposite is true for a diffusion‐controlled system. For either case an open ground surface contributes to a more rapid depletion of the residual liquid source. The advective mass flux caused by the release of vapor due to vaporization at the source is seen to be of minor importance. Copyright 1990 by the American Geophysical Union.