Multiscale quantification of LNAPL redistribution processes in multiphase systems under groundwater table fluctuation...

The groundwater table fluctuation (GTF) zone serves as the critical mass-transfer interface controlling light non-aqueous phase liquid (LNAPL) migration from the vadose zone into the aquifer, significantly influencing the transport of different LNAPL phases. However, the redistribution behaviors of LNAPL in water-medium-air systems under GTF remain unclear. This research investigated LNAPL redistribution under seasonal and diurnal GTF at a petroleum-contaminated site in northeastern China. LNAPL migration processes under GTF were categorized into dripping and smearing patterns, respectively. Furthermore, a 1D flow chamber packed with porous media was established under three-phase conditions, and LNAPL contents across dissolved-phase, volatile-phase, free-phase, and residual-phase under different patterns were systematically monitored using sampling analysis and light transmission visualization methods. The results demonstrated that LNAPL dissolution and volatilization were simultaneously governed by hydrodynamic conditions and the redistribution of entrapped LNAPL. GTF modified both free-phase LNAPL content and hydrodynamic conditions, thereby controlling the dynamic transformation process from free-phase to residual-phase LNAPL, with maximum transformation rates of 0.17 mL/min and 0.98 mL/min under dripping and smearing patterns, respectively. GTF drove LNAPL volatilization and dissolution, both exhibiting strong cycle dependence. After 6 GTF cycles, the volatilization flux increased by 13.6∼16.0 % and convective transport flux increased by 42.51∼70.60 % in dripping pattern, while in smearing pattern, the volatilization flux increased by 62.50∼88.24 % and convective transport flux decreased by 20.14∼40.26 %. These findings provide crucial theoretical foundations for predicting LNAPL migration pathways in contaminated sites and developing effective remediation strategies.