Bench-Scale Investigation on Vibrorecovery of NAPL Ganglia from Sands

Light non-aqueous-phase liquid (LNAPL) pools at the interface of unsaturated and saturated zones fluctuate with ground-water table and create a “smear zone” occupied by ganglia or blobs. These ganglia dissolve slowly and constitute a long-term threat to ground-water resources. Prior investigations reported in this journal indicated that vibrations, when induced locally in an LNAPL-contaminated porous medium, cause momentary particle rearrangement and provide necessary conditions for mobilization of these ganglia. These investigations were laboratory scale involving shaking table and sand columns. This paper reports on a bench-scale investigation of the implementation of vibrorecovery. A probe-type vibrator was used to create vibrations in a polyvinyl chloride tank filled with Soltrol-contaminated sand. The vibrator was housed in a well chamber wherein the NAPL ganglia, mobilized using controlled flow gradients, were collected before being pumped out. The flow domain around the vibrator was delineated using a dye tracer, and the density variations in the vibrated soil were determined. The design of the prototype vibrator was adequate in creating a zone of reduced LNAPL residual saturations in the flow domain.