THE IMAGING OF WETTING FRONT INSTABILITIES IN POROUS MEDIA USING NEUTRON RADIOSCOPY

The remediation of soil contaminated with organic substances such as gasoline products is a subject of growing concern. One method often employed is flooding the soil with water or a water-surfactant mixture to wash the contaminant down to the water table. The organics are then pumped out of the subsurface with the ground water for treatment. This procedure has produced only limited results. It has been speculated that this lack of success is due in part to what is known as wetting front instability. Wetting front instability can occur during infiltration of a liquid into porous media, particularly when a fine soil layer is overlying a coarse layer. Instability of the wetting front implies that the interface between the advancing fluid and the portion of the porous media still at initial conditions does not advance as a flat front, but rather it breaks up into finger-like flow paths. Through the use of neutron radioscopy and three-dimensional, computer reconstruction, three dimensional infiltration experiments, with water and organic liquids infiltrating into layered porous media, were conducted in an attempt to evaluate the influences of initial moisture content, and type of infiltrating fluid on the formation of fingers. Experimental data was also evaluated for the purpose of calibrating dimensionless relations for predicting finger properties such as finger diameter and propagation velocity