Description
Prediction of the transport of volatile mixtures within unsaturated soil can be complicated by the interaction of chemical compounds with variable physical properties. The analysis and design of vapor-extraction remedial systems depends on models which can simulate the chemical and physical factors affecting the removal of vapor-phase chemical mixtures (such as gasoline). Present models fall into two categories: 1) non-dimensional (no transport), multi-compound phase distribution models or 2) multi-dimensional, single-compound transport models. In this thesis, a numerical simulation is presented which couples the steady-state vapor flow equation, the advection-diffusion transport equation, and a multiple-compound, four-phase equilibrium model. The simulation allows spatially variable fields of permeability, surface leakage, and initial contaminant concentrations. The user can specify the location and discharge rates of any number of extraction or injection wells, including zero wells, in which case the simulation will solve transport by diffusion only. The utility of the model is shown by solving the remediation, by vapor extraction, of hypothetical gasoline spills in natural (non-ideal) conditions. The non-ideal conditions include inhomogeneous soil permeability, irregular surface leakage (from fill areas or surface seals), and irregular contaminant distribution. The model is also run in the pure diffusion mode to show the limitations of three-phase (no separate-phase), single-compound vapor flux models in predicting chemical fate and transport.
