Effect of spreading coefficient on the distribution of light non-aqueous phase liquid in the subsurface

We perform a series of three-phase gravity drainage experiments in columns containing two different sands and for three different light non-aqueous phase liquids (LNAPLs) — hexane, iso-octane and n-decane. The fluid system is chosen to have different values of the equilibrium spreading coefficient, which measures the tendency for LNAPL to spread on water. The final configuration of air, water and LNAPL in capillary/gravity equilibrium is measured using gas chromatography. We find that the saturation of LNAPL in the top part of the column for the hexane system could be as low as 0.1%, but that it increases with increasing soil heterogeneity and with decreasing spreading coefficient. We also measure the air/water distributions in capillary/gravity equilibrium to obtain the capillary pressure curve for each sand. Using a modified Leverett J function scaling, we predict the distribution of continuous LNAPL, water and air from a single capillary pressure curve and compare with our experimental results. The predictions match the measurements in the regions where the NAPL saturation is greater than 10%.