Dense nonaqueous phase liquids: Flow characterization and remediation

Release of dense nonaqueous phase liquids (DNAPLs) in the subsurface can cause aquifers to become contaminated and hazardous as a source of drinking water. These compounds are denser than water and their viscosity has a wide range of values. The DNAPLs have low solubility in water but are still far in excess of regulatory standards. Fingering of DNAPLs is expected to be different from the fluid displacement studies in petroleum engineering where the displacing fluid is preferentially wetting with respect to the medium. By comparison, DNAPL infiltration is displacement by a nonwetting liquid phase and should be regarded as a pore-scale process. Distribution of DNAPLs in a saturated porous medium is not understood. The aim of the present study is to improve our understanding of the instability phenomena that may accompany the transportation of DNAPLs and the dense plumes of the dissolved contaminants.; An X-ray Computed Tomography scanner was used to nonintrusively measure three-dimensional flow patterns at a resolution of 0.5 x 0.5 x 8 mm 3 per pixel during DNAPL infiltration. We have investigated the effect of density, viscosity and capillarity on the infiltration behavior of DNAPLs. In a low capillary pressure porous medium, complex finger patterns were generated by shielding, spreading and tip-splitting mechanisms. In high capillary pressure system, finger moved downward approximately resembling a cylinder. A nonzero critical velocity was observed for secondary finger development, even for an inherently unstable flow, in a high capillary pressure system.; The DNAPL remediation was conducted using a biodegradable (Glucopon) surfactant. Effect of surfactant concentration, flow rate and capillarity of the medium on the remediation process of tetrachloroethylene has been investigated. Mobilization of residual PCE was detected near the injection well for a high permeability system. Mobilization resulted in redistribution of PCE in the saturated porous media away from the injection well. For high permeability system, displacement is stable for high surfactant concentration and the displacement front becomes sharper with increasing surfactant flow rate. Displacement of the PCE from the saturated porous medium using surfactant was observed to be unstable for low permeability system. Also, macro-emulsion formation was detected for all combination of injection velocity and surfactant concentration.