Predictive models and airflow distribution associated with the zone of influence (ZOI) during air sparging...

Laboratory two-dimensional airflow visualisation model tests were conducted to assess the effect of particle size and air injection pressure on airflow patterns, physical characteristics of the zone of influence (ZOI) and the airflow rate distribution within the ZOI. The results indicate that the pattern transitions from chamber flow to channelized flow and then to bubbly flow occurred at effective particle sizes (D10) in the ranges 0.22-0.42 mm and 1.42-2.1mm, respectively. The ZOI is shaped like a conical frustum, and there exists a "stable ZOI" for each type of porous medium in channelised and bubbly flow during sparging tests. A formula for calculating the size of the ZOI radius was established based on the conical frustum-shaped results and the "stable ZOI", and comparing the calculated results with field data demonstrated that the formula has application value, except in large-scale heterogeneous aquifers. The distribution of the airflow rate within the ZOI, which is quite uneven, varies from the maximum rate (which occurred just above the sparger) to zero with the increase of the lateral distance from the sparger. Moreover, the airflow distribution can be fitted using a unified dimensionless Gaussian function under different sparging pressures for a given porous medium. All of the results described above provide valuable information for the design and theoretical modelling of air sparging for groundwater remediation.