Pilot scale experimental and numerical study of LNAPL pump and treat and transport in subsurface soil

Light nonaqueous-phase liquids (LNAPLs) are major organic contaminants in subsurface environment that accumulate above the water table after spills. Understanding their migration in the subsurface is crucial for effective remediation. This study investigates LNAPL transfer in sand tank experiments and simulations, focusing on spill, redistribution due to water table fluctuations, and pumping-based remediation. Experiments were performed in a large 3D sand-filled tank (5.2 × 3.6 × 3.6 m³) equipped with injection, pumping, and piezometric wells, as well as time domain reflectrometer (TDR) probes to monitor phase distribution and permittivity changes. The experimental results revealed key LNAPL migration patterns: an initial localized hump formed above the water table after a spill, which later spread into a flatter layer. Water table fluctuations caused residual LNAPL entrapment in the middle zone. Pumping created cones of depression near wells, while TDR probes detected permittivity changes linked to saturation shifts during water table cycles. To simulate multiphase flow, we used the continuity equation together with generalized Darcy's law, and applied the Stone I model to account for three-phase flow behavior. Experimental data, especially from piezometric wells, validated the numerical model, which effectively captured water-LNAPL and LNAPL-air interfaces. A mixing model for relative permittivity was also integrated, successfully reproducing TDR-observed trends across different tank regions. Overall, this work demonstrates that combining large-scale experiments with validated three-phase numerical simulations provides a reliable framework for predicting LNAPL behavior and optimizing remediation strategies at contaminated sites.