Mechanism study of the air migration and flowrate distribution in an aquifer with lenses of different permeabilities during air sparging remediation.

The poor performance of air sparging (AS) remediation in heterogeneous porous media is receiving increasing attention. However, understanding of the air migration and flowrate distribution mechanisms in heterogeneous aquifers is still lacking. In this study, for experimental purposes, a heterogeneous aquifer with lenses of different permeabilities was designed in the laboratory. The effects of the double interface between a lens and the background media on the air migration were visually observed for the first time, and four types of double interfaces and their related air flowrate distributions were identified. These were bimodal distribution (∆P ≤ -1.1 kPa, i.e., the air entry suction difference between the background media and the lens), fingered distribution for a low-permeability lens (-1.1 <∆P ≤ -0.3 kPa), Gaussian distribution (-0.3 <∆P < 0.4 kPa), and fingered distribution for a high-permeability lens (∆P ≥ 0.4 kPa). The experimental results indicated that double interface characteristics and air injection rates affected air accumulation behavior. A mathematical model was established to simulate the experimental data of the air flowrate distribution, and it could well describe the air flowrate distribution patterns in heterogeneous aquifers. These findings are significant for improving our understanding of the mechanisms of air migration and flowrate distribution in heterogeneous aquifers, leading to a better design and prediction of the AS remediation required for heterogeneous aquifer pollution.