Removal of dissolved- and free-phase benzene pools from ground water usingin situ air sparging

This paper presents the results of a laboratory investigation performed to study the use of air sparging to remediate dissolved-phase and free-phase [ or non-aqueous-phase liquid (NAPL)-phase] benzene pools from ground water. The specific objectives of the study were (1) to assess how air injection r ate affects the mass transfer and transport of dissolved- and NAPL-phase po ols; and (2) to determine the effect of groundwater how on the removal of d issolved- and NAPL-phase pools during the application of air sparging. A to tal of five 2D physical model tests were performed in a homogeneous coarse sand profile subjected to both static ground water and ground-water flow co nditions. Three different air injection rates were used in a static groundw ater condition, and two different air how rates were used in soil profiles subjected to ground-water flow (hydraulic gradient = 0.011). All tests were performed with similar initial dissolved- and NAPL-phase benzene condition s. Injected air traveled within a parabolic zone of influence tin channel m ode) when subjected to both static ground water and ground-water flow condi tions, indicating that ground-water flow (for the ground-water velocities t ested) did not affect the injected air zone of influence. An increase in ai r injection rate led to faster contaminant removal; however, at higher air injection rates, a threshold rate of removal was reached above which furthe r increases in injection rate are a waste of effort. Additionally, air inje cted into the soil profile reduced the hydraulic conductivity within the zo ne of influence. This in turn led to lower ground-water flow rates, allowin g for effective interception and treatment of a migrating NAPL plume. Highe r air injection rates led to further reductions in hydraulic conductivity, allowing for substantial control of the NAPL plume in the downgradient dire ction. Overall, this study showed that air sparging can be used to effectiv ely remediate dissolved- and NAPL-phase benzene.