MODELING OF AIR SPARGING IN A LAYERED SOIL - NUMERICAL AND ANALYTICALAPPROXIMATIONS

Air sparging in an aquifer below a less permeable horizontal layer is modeled using a two-phase flow approach. Supported by numerical simula tions, we show that a steady state situation is reached. For an analys is of the steady state, we distinguish three different flow regimes, w hich occur between the well screen and the unsaturated zone. Just belo w the interface that separates the high and the low permeable layers a regime with almost hydrostatic capillary pressures develops. We use t his observation to derive an ordinary differential equation for the pr essure at the interface, which leads to an approximation of the air fl ow pattern just below and within the low permeable laver. The approxim ation provides an estimate for the radius of influence as a function o f the physical parameters. The agreement between the analytical approx imation and the numerical steady state results is almost perfect when heterogeneity is increased. With a few modifications the analysis appl ies also to a dense non-aqueous phase liquid (DNAPL) spill above a les s permeable layer. Comparison with an illustrative numerical simulatio n shows that the analytical approximation provides a good estimate of the radial spreading of the DNAPL flow on top of and within the low pe rmeable layer.