Experimental investigation and conceptual model development for multiphase flow in a water-wet porous medium with NAPL-wet soil lenses

The remediation of Brownfield sites impacted by non-aqueous phase liquids (NAPLs) remains a challenge. Many of the multiphase flow simulators and remediation technologies developed have assumed that the soils are water-wet. Yet several studies have suggested that the assumption of water-wet conditions may not be valid for a number of field sites. In addition, the processes that impact the magnitude and distribution of the residual NAPL saturation term are not well defined in water-wet porous media and in water-wet porous media with NAPL-wet soil lenses. Therefore, this research focuses on performing experimental work at the pore scale and the representative elementary volume (REV) scale to gain a better understanding of the NAPL distribution in a water-wet porous medium with NAPL-wet soil lenses. The experimental study included measuring capillary pressure-saturation (Pc-S) relationships in two and three-phase systems, and residual NAPL saturations measured under a large range of experimental conditions.;This research also includes development and validation of a new conceptual model for the residual NAPL saturation term in a water-wet porous medium. The new model assumes that the effective residual NAPL saturation depends on eight parameters; porous medium specific surface area, NAPL entry pressure head in NAPL/water two-phase system, porous medium grain size distribution, porous medium porosity, NAPL film thickness, apparent water saturation, historic maximum apparent NAPL saturation, and the absolute maximum effective residual NAPL saturation in the porous medium. The research also includes development and validation of new conceptual models for the residual NAPL saturation term in a water-wet porous medium with isolated or connected NAPL-wet soil lenses. The model predications were compared to the effective residual NAPL saturations measured under a large range of experimental conditions. In most cases, the models were capable of predicting the measured effective residual NAPL saturations.;The experimental study was followed by development and validation of conceptual models for Pc-S relationships for air/NAPL, air/water, and NAPL/water two-phase systems as well as for an air/NAPL/water three-phase system for a water-wet porous medium with NAPL-wet soil lenses. The approach taken in this research was to consider the water-wet porous medium with NAPL-wet soil lenses as the field scale REV and to derive constitutive relationships for this REV scale based on our knowledge of the constitutive relationships of each soil fraction (i.e., water-wet and NAPL-wet). The experimental results indicated that the Pc-S relationship for an REV with NAPL-wet soil lenses could be constructed based on a volume-weighted summation of the Pc-S relationship for each soil fraction. Special attention is needed to address the isolation of NAPL within the NAPL-wet soil lenses as water imbibes into the system as this may substantially increase the entrapped NAPL saturation.