Determination of specific NAPL–water interfacial areas of residual NAPLs in porous media using the interfacial tracers technique

We present here an application of a new experimental method called the `interfacial tracers techniqueʹ (IFTT), using tracer retardation by adsorption as the basis, to determine the specific NAPL–water interfacial areas (anw, cm2/cm3) in packed columns of sand and glass beads containing residual saturation of non-aqueous phase liquid (NAPLs). Four NAPLs, two types of sand and uniform glass beads, and two interfacial tracers were used in the tracer experiments. The anw values determined for residual NAPLs in sand or glassbead columns were in the range of 60 to 300 (with one exception of 1200) cm2/cm3, and are in agreement with the current understanding of immiscible fluid behavior in porous media. For a given NAPL, the anw value was found to be about twice as large when the porous medium was NAPL wet first, compared to when the medium was first water wet. The interfacial tracer technique will be useful in assessing NAPL morphology, dissolution and mass transfer, and is useful in the characterization and remediation assessment at NAPL-contaminated waste sites.