The effects of water table fluctuation on diesel fuel redistribution in unsaturated soil are investigated in the laboratory by one-dimensional column test. The simplified image analysis method is used to assess the saturation distributions of water and diesel in the flow domain under transient condition. The experiments are undertaken on two homogeneous sands to study the effects of different particle sizes. The two-phase experimental data illustrate soil-liquid characteristic curves (SLCCs) of water/air and diesel/air systems. The SLCCs of diesel/water systems can be predicted by scaling procedure. A descending order of matric suction at a given saturation of wetting phase is in the order of air/water, diesel/water and air/diesel systems. Coarser particle size gives smaller entry pressure, residual matric suction and residual degree of saturation. The three-phase (air/water/diesel) experimental data illustrate that, during imbibition stages, air and diesel are entrapped below water table with the entrapped air saturations of 18-24% and entrapped diesel saturations of 6-10% for fine sand. Coarser particle size yields smaller entrapped diesel saturations and larger entrapped air saturations. The residual diesel saturations during drainage stages and entrapped diesel saturations during imbibition stages do not show any systematic difference as these stages are repeated. During imbibition stages, 37-47% of the total amount of diesel fuel is entrapped under the water table. Also, there is no systematic difference in the amount of diesel fuel entrapped under the water table when imbibition stages are repeated.

The correct understanding of the dynamic behavior of Light Non-Aqueous Phase Liquids (LNAPLs) under fluctuating groundwater conditions, difficult to test with conventional methods, is important for the adequate remediation of contaminated soils. In this study, we verified the suitability of the Simplified Image Analysis Method (SIAM) as a tool to assess the saturation distribution of water and Non-Aqueous Phase Liquids (NAPLs) in granular soils, by testing its basic assumption, the existence of a linear relationship between water saturation (Sw), NAPL saturation (So) and optical density (Di), for nine different NAPLs. We then utilized SIAM to study the dynamic behavior of four different LNAPLs that were infiltrated to 1D columns filled with Toyoura sand, and later subjected to two cycles of drainage-imbibition of the water table. It was found that, under similar conditions, the depth of LNAPL infiltration was linearly correlated to the viscosity of the contaminants (R2 = 0.84), the difference between the depth of the mobile fraction after both drainage and imbibition stages was linearly correlated to the interfacial tension values (R2 = 0.79), and the viscosity was logarithmically correlated to the residual saturation ratios for all different NAPLs (R2 = 0.95), correlations that can help us understand and predict the behavior of different contaminants when spilled in the ground.