Effects of process control changes on aquifer oxygenation rates during in situ air sparging in homogeneous aquifers

In situ air sparging is used to remediate petroleum fuels and chlorinated solvents present as submerged contaminant source zones and dissolved contaminant plumes, or to provide barriers to dissolved contaminant plume migration. Contaminant removal occurs through a combination of volatilization and aerobic biodegradation: thus, the performance at any given site depends on the contaminant and oxygen mass transfer rates induced by the air injection. It has been hypothesized that these rates are sensitive to changes in process flow conditions and site lithology, but no data is available to identify trends or the magnitude of the changes. In this work, oxygenation rates were measured for a range of air injection rates, ground water now rates, and pulsing frequencies using a laboratory-scale two-dimensional physical model constructed to simulate a homogeneous hydrogeologic setting. Experiments were conducted with water having low chemical and biochemical oxygen demand. Results suggest the following: that there is an optimum air injection rate; advective flow of ground water can be a significant factor when ground water velocities are > 0.3 m/d; and pulsing the air injection had little effect an the oxygenation rate relative to the continuous air injection case.