Modeling water–NAPL–air three-phase capillary behavior in soils

Existing models relating the capillary pressures and the degrees of saturation of NAPL, water, air three-phase are briefly reviewed, and their limitations are discussed. Of particular interest is their inability to describe the intrusion and emission behavior of NAPL precisely, especially when the degree of saturation of NAPL is low. A new variable μ representing the relative magnitude of NAPL pressure to water pressure and air pressure is then defined as a state parameter, and a novel water–NAPL–air three-phase model is proposed, which considers the transition phenomena between water–NAPL–air three-phase and arbitrary two-phase system through the parameter μ. The validity of the proposed model is checked by comparing the calculation results with those obtained by an ordinary model and existing experimental results. The proposed model is shown capable of properly considering the interactions among the water–NAPL–air three-phase, and predicting the actual retention behavior of NAPL in unsaturated ground.