OIL MOBILITY IN WATER-SATURATED GRANULAR MEDIA AND EMERGENCY ACTION FOR CONTAINMENT

Methodologies are presented to set up emergency action for containing hydrocarbon spills on soil in order to prevent contamination spread to the groundwater while site remediation is accomplished. The mobility of oils in water-saturated granular porous media is first discussed, mainly based on visual observations during lab-scale experiments. Conditions for oil mobility and its flow morphology in such media were defined using two dimensionless numbers: Bond (Bo) and capillary (Ca) number. Several oils were tested: hexane, hexadecane, α- methylnaphthalene and perchloroethylene. Different operating conditions were considered: stagnant water, vertical and horizontal water flow. Application of gelled polymer technology to create a barrier to contaminant transport in soils is then discussed. Xanthan gum aqueous solutions were tested with different crosslinking agents: Xanthan gum is a biopolymer which is neither toxic to humans nor to the ecosystem. Chromium (III) salts, Aluminum (III) salts and gaseous CO2 solutions were used as crosslinking agents. Apparent viscosity of xanthan aqueous solutions was investigated as a function of shear rate. They show low viscosity at high shear rate, making injection in a porous medium easier, and high viscosity at low shear rate making the solution motionless after injection. Gelation time may be instantaneous or may last weeks depending on the crosslinking agent adopted and its concentration. If Al(III) is adopted gel formation occurs at low pH. Therefore, acid must be added to the solution. However, the gelation process is instantaneous. Therefore, the addition of the acid agent must be performed in situ after injection of the xanthan solution. If Cr(III) is the crosslinking agent, gelation occurs in a range from a few hours to weeks depending on the chromium salt adopted. In this case the xanthan and chromium salt solutions can be injected at the same time. Chemical resistance of the gel formed was tested using few hydrocarbons. No attack to the gel structure was observed after more than 6 months.