LABORATORY AND MODEL SIMULATIONS OF A LNAPL SPILL IN A VARIABLY-SATURATED SAND .1. LABORATORY EXPERIMENT AND IMAGE-ANALYSIS TECHNIQUES

A two-dimensional, multiphase flow experiment was conducted in the lab oratory. The saturation distribution of a lighter than water non-aqueo us-phase liquid (LNAPL) as it migrated through a variably-saturated sa nd medium was determined using image analysis techniques. The pressure s in the water and LNAPL phases were measured using hydrophilic and hy drophobic porous cups connected to a series of pressure transducers an d a data acquisition system, The LNAPL inflow and water outflow were a lso recorded. A series of capillary pressure-saturation experiments we re conducted for each two-phase system. The capillary pressures record ed by the pressure transducers were used to calculate the phase satura tions based on a fully hysteretic capillary pressure-saturation algori thm. The static equilibrium capillary pressure-saturation relationship s proved to be invalid immediately ahead of the LNAPL front. The capil lary pressure-saturation relationship appeared to be dynamic for short periods of time as the LNAPL front arrived at each transducer locatio n. The presence of an entrapped air phase as the LNAPL migrated throug h the unsaturated zone clearly affected the migration of the LNAPL and the maximum LNAPL saturation reached in the sand medium.