Influence of Organic Acid Solution Chemistry on Subsurface Transport Properties. 2. Capillary Pressure−Saturation

Abstract

Two-phase flow models of subsurface transport often require the constitutive relationship of capillary pressure as a function of saturation as part of the data input. This part of the study correlates the solution chemistry findings from the previous paper with observed changes in the primary drainage capillary pressure−saturation relationship for a fine- to medium-grained quartz porous medium. The results showed that the solution chemistry was directly reflected in the capillary pressure−saturation relationship. The major factor determining the degree of reduction in capillary pressure was the concentration and speciation of octanoic acid dissolved in the aqueous phase, the same variables reported in part 1 as critical in determining the surface and interfacial tension. Because measurements of the contact angle showed that the system stayed strongly hydrophilic under all conditions, the capillary pressure relationships could be scaled adequately using the appropriate values of surface or interfacial tension only. Since organic acid speciation had opposite effects on capillary pressure in the air−water and o-xylene−water systems, the impact of pH on the movement of a contaminant front will depend on whether the contamination occurs in the vadose zone (air−aqueous phase system) or saturated zone (organic liquid−aqueous phase system).