Abstract: After entering underground, light non-aqueous phase liquid (LNAPL) will firstly migrate vertically in unsaturated zone, and then form a saturated lens above the water table when reaching the capillary zone. Precisely predicting the lens thickness in the capillary fringe is of great significance for the restoration of polluted aquifer. The authors measured the initial drainage curve and initial wetting curve of the water-oil phase through laboratory experiment, and then fitted the entry pressure with the saturation-pressure curve. According to the relationship between the drainage entry and wetting entry pressures when the lens become stable, a method to predict the thickness of the lens was established. A case study of medium sand and coarse sand shows that the predicted thickness of the lenses are 4.61 and 1.29 cm,respectively;while by laboratory experiments, the measured lens thickness are 5.30, 1.50 cm, respectively. The relative errors between the predicted and measured results are 13.0%, 14.0%, respectively. We can hardly get the absolute drainage or wetting curves in laboratory, therefore the lens thickness predicted is smaller than measured in laboratory.

Key words: light non-aqueous phase liquid, lens, saturation-pressure curve