AN UPDATED MODEL OF INDUCED AIR-FLOW IN THE UNSATURATED ZONE

Simulation of induced movement of air in the unsaturated zone provides a method to determine permeability and to design vapor extraction rem ediation systems. A previously published solution to the airflow equat ion for the case in which the unsaturated zone is separated from the a tmosphere by a layer of lower permeability (such as a clay layer) has been superseded. The new solution simulates airflow through the layer of lower permeability more rigorously by defining the leakage in terms of the upper boundary condition rather than by adding a leakage term to the governing airflow equation. This note presents the derivation o f the new solution. Formulas for steady state pressure, specific disch arge, and mass flow in the domain are obtained for the new model and f or the case in which the unsaturated zone is in direct contact with th e atmosphere.