R.B. Mapa and T.H. Illangasekare

Department of Civil, Environmental and Architectural Engineering, University of Colorado at Boulder, Boulder, CO, 80309-0428, 303-492-6754


Many numerical models developed to describe the two phase flow of hazardous organic liquids in the subsurface requires the capillary pressure saturation relationship as an input parameter. Due to the lack of data, a variety of techniques are used in multiflow flow models for estimation of capillary pressure saturation relationship for the liquids and conditions prevailing at hazardous waste sites. Furthermore these estimations are limited mostly to drainage curves neglecting the hysteresis effect. This paper present a new and rapid method to obtain the capillary pressure saturation relationship using a flexible wall permiameter and a continuous flow pump. The advantages of this method include eliminating artificially large pores between the sample container and porous medium, achieving complete initial saturation as the sample can be tested at elevated pressures, and obtaining complete drainage and imbibition curves in 4 to 5 days.

The porous medium used was a crushed and sieved industrial silica sand with a mean grain size of 0.41 cm. The drainage and imbibition capillary pressure saturation relationships were first obtained for a water/air system. Water was withdrawn at a rate of 1 cc/h using a continuous flow pump from the initially saturated sample through the bottom porous plate. At the same time the non-wetting fluid (air) was allowed to enter from the top of the sample. The differential pressure between the non-wetting phase at the top and the wetting phase at the bottom was recorded at 100 second intervals using a pressure transducer and a data acquisition system. At residual saturation the direction of the pump was reversed to obtain the imbibition curve. The porosity of the sample and the pump rate was used to calculate the saturation corresponding to pressure measurements. The same sample was then tested for a water/p-xylene system. P-xylene was allowed to enter from the top of sample as the non-wetting fluid, instead of air, while water was withdrawn from the bottom of the sample. The drainage and imbibition capillary pressure relationships for the water/air and water/p-xylene systems will be presented.


capillary pressure saturation relationship, porous medium, two phase systems

This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.