Air Sparging (AS) is a widely used remediation method for removal of volatile contaminants from the groundwater. In AS, air is injected into the groundwater below the contaminant plume (see fig. 1). The injected air serves as a carrier for contaminants as it travels through the porous media towards the surface where it is captured by a vapor extraction system.
Following initiation of air injection, the dynamics of the air injection process has three distinct stages: (1) The initial stage, where channels form and expand in both lateral and vertical directions. This stage ends when channels penetrate the unsaturated zone; (2) a transient stage, in which the airflow region shrinks and some channels collapse. This leads to a reduction of channel span in the lateral direction; (3) a steady-state regime where air channels remain static for as long as other system parameters remain unchanged.
In the 3rd stage only the contaminants in close proximity to the channels are removed, whereas contaminants further away are left untreated, since the dominant transport mechanism is diffusion. Hence, the efficiency of the remediation system declines over time.
Recent studies have reported pronounced advantages to applying AS in a pulsed operation rather than in a continuous operation. When the system is turned off, water flows radially, towards the injection well. Turning the system back on, water is "pushed" outward. This back-forward motion continuously moves contaminant (being transported by water), and improves their chance to be "captured" in the proximity of a newly formed channel.
We propose a revised AS system in which the injection rate is altered right before the system turns into the 3rd, steady state stage, using a large range of injection rates. We hypothesize that using multiple injection rates, a faster and more efficient treatment to contaminants will be achieved due to enhanced mixing allowing contaminants to be removed from areas with lower hydraulic conductivity.
