Analysis of oil lens removal by extraction through a seepage face

Removal of LNAPL (oil) from an aquifer is described using a multi-phase flow model. At the well boundary seepage face conditions are imposed. These conditions are implemented in a numerical model and withdrawal in a two-dimensional domain is simulated for two different geometries of the oil lens and for varied values of the physical parameters. Assuming vertical equilibrium, the oil flow equation is reduced by vertical integration. The well boundary condition is approximated by imposing zero oil lens thickness. Similarity solutions of the reduced equations for the two geometries show good agreement with the numerical results in most cases

Modelingof air sparging in a layered soil : numerical and analytical approximations

Air sparging in an aquifer below a less permeable horizontal layer is modeled using a two-phase flow approach. Supported by numerical simulations we show that a steady state situation is reached. For an analysis of the steady state we distinguish three different flow regimes, which occur between the well screen and the unsaturated zone. Just below the interface, that separates the high and the low permeable layers, a regime with almost hydrostatic capillary pressures develops. We use this observation to derive an ordinary differential equation for the pressure at the interface, which leads to an approximation of the air flow pattern just below and within the low permeable layer. The approximation provides an estimate for the radius of influence as a function of the physical parameters. The agreement between the analytical approximation and the numerical steady state results is almost perfect when heterogeneity is increased. With a few modifications the analysis applies also to a DNAPL spill above a less permeable layer. Comparison with an illustrative numerical simulation shows that the analytical approximation provides a good estimate of the radial spreading of the DNAPL flow on top of and within the low permeable layer

Three-phase flow analysis of dense nonaqueous phase liquid infiltration in horizontally layered porous media

We considered dense nonaqueous phase liquid (DNAPL) infiltration into a water-unsaturated porous medium that consists of two horizontal layers, of which the top layer has a lower intrinsic permeability than the bottom layer. DNAPL is the intermediate-wetting fluid with respect to the wetting water and the nonwetting air. The layer interface forms a barrier to DNAPL flow, which causes the DNAPL to spread out horizontally just above the interface. An analytical approximation has been developed to estimate the DNAPL pressure and saturation and the horizontal extension of the DNAPL above the layer interface at steady state for low water saturations. The analytical approximation shows that the DNAPL infiltration is determined by five dimensionless numbers: the heterogeneity factor ¿, the capillary pressure parameter ¿, the gravity number N g , the ratio of the capillary and gravity numbers N c /N g , and the critical DNAPL pressure P o c . Its predictions were compared with the results of a numerical three-phase flow simulator for a number of parameter combinations. For most of these combinations the analytical approximation predicts the DNAPL pressure and saturation profiles at the interface adequately. Using the analytical approximation, we carried out a sensitivity study with respect to the maximum horizontal extension of the plume. The extension of the plumes appears to be highly sensitive to variation of the dimensionless numbers P o c , ¿ and

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(LNAPL)on a horizontal water table with emphasis on the effect ofNAPLentrapment 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 theLNAPLlens 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 anLNAPLlens and the amount ofNAPLthat becomes trapped, of theLNAPLremoval rate and the extension of the remainingNAPLin case of extraction, and of the air sparging radius of influence in a homogeneous and in a layered soil