An experimental investigation of the capillary pressure - saturation relation in two- and three-fluid porous media

Attempts to model the separate phase transport of contaminants in the subsurface have been hindered by a scarcity of constitutive data, especially for the three-fluid case. The research reported here has developed and tested laboratory techniques for examining the variation of capillary pressures with fluid saturations in porous media containing up to three fluids.;As a first step, a technique was developed which permits the application of dual-gamma attenuation to measurements of the saturations of three immiscible fluids in a porous solid whose bulk density is independent of changes in fluid content. The potential of this technique for use in laboratory studies relevant to contaminant transport problems was demonstrated in an experimental application in which the fluid contents of air, water and trichloroethylene or tetrachloroethylene in sand samples were measured. Theoretical analysis indicates that the technique is useful for multiply halogenated hydrocarbons in general. The dual-gamma technique may also be applied to transient systems.;A standard technique for measuring suction in air-water soil column experiments was adapted for use in systems containing more than one liquid. Pairs of tensiometer probes (hydrophilic and hydrophobic) were used to maintain hydraulic contact between (aqueous and nonaqueous) liquids within the medium and external pressure sensors. Naturally hydrophilic ceramic probes were siliconized to produce hydrophobicity.;A set of two-fluid (air-water, air-PCE and PCE-water) and three-fluid (air-PCE-water) capillary pressure - saturation drainage curves were generated using dual-gamma attenuation and tensiometer pairs. Standard two-fluid models (Brooks-Corey and van Genuchten models) for the capillary pressure - saturation relation were fit to two-fluid data sets. Data from three-fluid tests were analyzed to produce two relations: gas-PCE capillary head versus total liquid saturation and PCE-water capillary head versus water saturation. The assumption of equivalence between two-fluid and three-fluid relationships was tested. Agreement between two- and three-fluid cases was found to be good for the PCE-water case, questionable for the air-PCE case.