Effect of Flow Rate Changes and Pulsing on the Treatment of Source Zones by in Situ Air Sparging

Abstract

Laboratory-scale two-dimensional aquifer physical model studies were conducted to qualitatively assess how changes in air injection rate, air injection pulsing, and chemical type affect the rate and extent of removal by in situ air sparging. In this work, the treatment of immiscible-phase source zones in coarse media has been simulated. To provide a basis for comparison, equivalent unsaturated-soil soil vapor extraction-like simulation experiments were also conducted. Results suggest that, (i) initially, removal occurs from within saturated zone air flow channels at rates similar to those observed for soil vapor extraction, (ii) during this initial period, removal rates are proportional to air flow rate and equilibrium chemical vapor concentrations, (iii) while increased air injection rates improve volatilization rates in the short-term, the long-term cumulative removal efficiency may not be affected unless the saturated zone air flow distribution changes significantly with flow rate, (iv) pulsing the air injection can improve the long-term cumulative removal efficiency, and (v) while short-term removal efficiency improves with increasing flow rate and vapor pressure, the long-term removal efficiency appears to improve with increasing solubility.