The importance of fluid entrapment, saturation hysteresis and residual saturations on the distribution of a lighter-than-water non-aqueous phase liquid in a variably saturated sand medium

A two-dimensional, multiphase flow experiment was conducted in the laboratory and numerically modelled using a finite difference multiphase flow code. Heptane, a lighter-than-water non-aqueous phase liquid (LNAPL), was spilled on a variably saturated sand medium. After the spill was completed, the LNAPL was allowed to distribute itself above the capillary fringe. The water pressure at the base of the experimental box was subsequently raised and lowered on two separate occasions to simulate fluctuating water table conditions. The water and LNAPL pressures were measured using hydrophillic and hydrophobic porous cups connected to pressure transducers and a data acquisition system. The laboratory spill was modelled using a hysteretic and non-hysteretic multiphase flow code. A comparison of the experimental data to the model results illustrates the effects and importance of fluid entrapment and saturation hysteresis.