Multi-phase flow modeling of soil contamination and soil remediation.

In this thesis multi-phase flow models are used to study the flow behavior of liquid contaminants in aquifers and of gases that are injected below the groundwater table for remediation purposes. Considered problems are redistribution of a lens of light nonaqueous phase liquid<TT>(LNAPL)</TT>on a horizontal water table with emphasis on the effect of<TT>NAPL</TT>entrapment by water and its removal through a well with appropriate multi-phase seepage conditions at the well boundary. In addition, air injection into groundwater (air sparging) in a homogeneous soil and in a layered soil are modeled. Accurate but very time-consuming numerical simulations for the various problems are performed. For further analysis appropriate reductions are made. Assuming vertical equilibrium and vertical averaging of the flow equations reduce the geometrical dimensionality of the<TT>LNAPL</TT>lens problems and of the problem of air sparging in a layered soil. The air sparging problems are analyzed at steady state, which eliminates the time dependence. Sparging in a homogeneous soil admits further reduction by neglecting capillary forces in vertical direction. For all problems the resulting equations are of nonlinear diffusion type, that can be cast into the porous medium equation. For the various problems similarity solutions to the porous medium equation exist, that show good agreement with numerical results. These analytical solutions give the main features of the spreading velocity of an<TT>LNAPL</TT>lens and the amount of<TT>NAPL</TT>that becomes trapped, of the<TT>LNAPL</TT>removal rate and the extension of the remaining<TT>NAPL</TT>in case of extraction, and of the air sparging radius of influence in a homogeneous and in a layered soil