AN EXPERIMENTAL-STUDY OF COMPLETE DISSOLUTION OF A NONAQUEOUS PHASE LIQUID IN SATURATED POROUS-MEDIA

The attenuation of gamma radiation was utilized to measure changing re sidual trichloroethylene (TCE) saturation in an otherwise water-satura ted porous medium as clean water was flushed through the medium. A fro nt over which dissolution actively occurred was observed. Once develop ed, this front varied in length from approximate to 11 mm to approxima te to 21 mm, lengthening as it moved through the porous medium. Gamma attenuation measurements and analyses of effluent water samples indica te that there was minimal if any transport of TCE as colloidal droplet s. Even as trapped TCE ganglia decreased in size due to dissolution, t here is no evidence that they became mobile and advected downgradient. An extraction of the porous medium at the completion of one experimen t indicated that less than 0.002% of the original TCE mass remained, s uggesting that minimal amounts of separate phase TCE remained trapped within the medium after flushing with 290 pore volumes. Mass transfer rate coefficients were computed and are shown to be a function of Darc y flux, TCE volumetric content, and distance into the region of residu al TCE.