A model for flow induced by steady air venting and air sparging

A numerical model for the axisymmetric subsurface flow during steady air venting and/or sparging from underground wells along the same vertical axis is presented. A common observation that for steady air injection or extraction, motion of the groundwater is negligible is first justified theoretically. Thus in the two-phase problem, only air is moving, while water remains stationary. Nevertheless there can be significant changes in water saturation because the capillary pressure varies nonlinearly with the air saturation. For pure air venting, the effects of upconing of the water table are studied. For pure air sparging, the role of air compressibility ignored by earlier authors is reassessed, and issues of design interest such as the radius of influence and discharge rates are examined. Comparisons with published measurements are discussed. Physical implications of concurrent venting and sparging are also discussed.