THE IMPORTANCE OF FLUID ENTRAPMENT, SATURATION HYSTERESIS AND RESIDUAL SATURATIONS ON THE DISTRIBUTION OF A LIGHTER-THAN-WATER NONAQUEOUS PHASE LIQUID IN A VARIABLY SATURATED SAND MEDIUM

A two-dimensional, multiphase flow experiment was conducted in the lab oratory and numerically modelled using a finite difference multiphase flow code. Heptane, a lighter-than-water non-aqueous phase liquid (LNA PL), was spilled on a variably saturated sand medium. After the spilt was completed, the LNAPL was allowed to distribute itself above the ca pillary fringe. The water pressure at the base of the experimental box was subsequently raised and lowered on two separate occasions to simu late fluctuating water table conditions. The water and LNAPL pressures were measured using hydrophillic and hydrophobic porous cups connecte d to pressure transducers and a data acquisition system. The laborator y 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 saturat ion hysteresis. (C) 1997 Elsevier Science B.V.