Modeling gas migration through unsaturated soils from waste disposal sites

Abstract

The movement of gases away from waste disposal sites and hazardous waste spills through soils can result in serious safety and health hazards. As in the analogous problem of contaminant transport in groundwater, mathematical models are useful in predicting future gas excursion distances at existing sites and evaluating gas migration control alternatives. This paper presents a mathematical model for simulating the migration of gases from waste disposal sites through the unsaturated zone. The system equations used to represent gas migration through the unsaturated zone are an amalgam of the traditional groundwater flow-contaminant transport equations with the representation of gaseous flows in molar quantities. The model accounts for gas migration due to gas pressure, concentration and velocity gradients. The system equations are solved with the Galerkin finite element technique. The mathematical model successfully reproduced observed historical gas pressure and concentration data at two landfill sites. These two applications tested the mathematical model for both summer and winter flow conditions and under both natural and forced gas potential gradients.