Characterization Of Air-Sparging For Groundwater Using ERT & Modeling Techniques

Air sparging(AS) has become a popular approach toward remediating groundwater contaminated with volatile organic compounds(VOCs) and chlorinated solvents. Its advantages of low-cost, high-efficiency and high-operability have been fully demonstrated in lots of researches. However, the related mechanism of the composite function besides physics, chemistry, biology in the AS processes is not yet clear. System design has remained largely empirical during air sparging field application. Little was known about the material removal mechanism of air sparging. The AS performance and ultimately contaminant removal are highly dependent on the pattern and type of subsurface air flow during the AS process. Traditional methods of monitoring the zone of influence(ZOI) depend on the monitoring wells including drilling, sampling for dissolved oxygen and groundwater leveling and so on. The disadvantages of high-cost, large staff demand and slow response, at the same time, brings the destructive disturbances to the field. So the electrical resistivity tomography(ERT) as a non-intrusive monitoring method can effectively understand the AS and related processes. Meanwhile, numerical models based on the theory of multiphase fluid mechanics for the axisymmetric subsurface airflow was developed in the study.Therefore, this paper presents the results of a laboratory experimental study which investigated the injected air flow development pattern with ERT by controlling the factors such as the porous medium material sorting, grain sizes and air flow rates. ERT with high sensitivity and accuracy has been proved to be more convenient and effective. A linear relationship holds between the pressure and flow rate of air in the porous medium. Air saturation around the injection port has a symmetric profile distribution in the well-sorted porous medium. The air saturation is bigger in the center; it will gather and select a few preferential passes when air encountered the low permeability areas in the heterogeneous porous media. When the aeration flow is so large that air is liable to lateral drift, local preferential flow is easy to form. At the same time, the ZOI of air flow was mainly affected by air flow and air injection pressure, nothing to do with particle size which normally influences air flow pattern. Moreover, the bubbly flow occurred at the 3 mm media and the channel flow for the 1 mm and 0.5 mm size media which had tortuous and decentralized air flow channels. The chamber flow differed significantly from channelized flow and pervasive/bubbly flow, which occurred at heterogeneous medium. An axisymmetric airflow model was set up based on Darcy Law and the Bessel function transform in combination with experimental conditions and soil-water characteristic curves of the FX and VG models. The models have been validated with experimental simulations which can be in consonance with the experimental data fairly well.