INFLUENCE OF ORGANIC-ACID SOLUTION CHEMISTRY ON SUBSURFACE TRANSPORT-PROPERTIES .2. CAPILLARY PRESSURE-SATURATION

Two-phase flow models of subsurface transport often require the consti tutive relationship of capillary pressure as a function of saturation as part of the data input. This part of the study correlates the solut ion chemistry findings from the previous paper with observed changes i n the primary drainage capillary pressure-saturation relationship for a fine- to medium-grained quartz porous medium. The results showed tha t the solution chemistry was directly reflected in the capillary press ure-saturation relationship. The major factor determining the degree o f reduction in capillary pressure was the concentration and speciation of octanoic acid dissolved in the aqueous phase, the same variables r eported in part 1 as critical in determining the surface and interfaci al 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 appropria te values of surface or interfacial tension only. Since organic acid s peciation had opposite effects on capillary pressure in the air-water and o-xylene-water systems, the impact of pH on the movement of a cont aminant front will depend on whether the contamination occurs in the v adose zone (air-aqueous phase system) or saturated zone (organic liqui d-aqueous phase system).