Centrifuge modeling of air sparging - a study of air flow through saturated porous media

The success of air sparging as a remedial technology for treatment of conta minated aquifers is well documented. However, there is no consensus, to dat e, on the mechanisms that control the flow of injected air through the satu rated ground. Currently, only qualitative results from laboratory experimen ts are available to predict the zone of influence of a sparging well. Given that the patterns of air flow through the soil will ultimately determine t he efficiency of an air sparging treatment, it is important to quantify how sparged air travels through a saturated porous medium. The main objective of this research is to develop a model that describes air transport through saturated porous media. This paper presents results from an ongoing study that employs centrifuge modeling to reproduce in situ air sparging conditio ns. Centrifuge testing is an experimental technique that allows reduced-sca le duplication, in the laboratory, of the stresses and pressure distributio ns encountered in the field. In situ conditions are critical in the develop ment of actual air flow patterns. Experiments are being conducted in a tran sparent porous medium consisting of crushed borosilicate glass submerged in fluids of matching indices of refraction. Air is observed as it flows thro ugh the porous medium at varying gravitational accelerations. Recorded imag es of experiments allow the determination of flow patterns, breakthrough ve locities, and plume shapes as a function of g-level and injection pressure. Results show that air flow patterns vary from fingering, at low g-levels, to pulsing at higher accelerations. Grain and pore size distribution of the porous medium do not exclusively control air flow characteristics, Injecto r geometry has a definite effect on breakthrough velocities and air plume s hapes. Experiments have been conducted to compare the velocity of air Row t hrough the saturated porous medium to that of air in pure liquids. Results show that the velocity of air through the medium is lower than that in the pure fluid, as expected. At high g-levels however, plume breakthrough veloc ities are proportional to the velocity of the air in the pure fluid. (C) 20 00 Elsevier Science B.V. All rights reserved.