Oil mobility in water-saturated granular media and emergency actions for the containment

Methodologies are presented to arrange emergency actions for containing spills of hydrocarbons on soil in order to avoid that they spread out and eventually reach the aquifer in the mean time that a site remediation activity is accomplished. Firstly a discussion on the mobility of oils in water-saturated granular porous media is presented mainly based on visual observations obtained during lab-scale experiments. Conditions for the oil mobility and the morphology of its motion in water-saturated granular media have been defined using two dimensionless numbers: Bond (Bo) and Capillary (Ca) number. Several oils have been tested: Hexane, Hexadecane, -methylnaphtalene, Perchloroethylene. Different operating conditions were considered: stagnant water, water moving in the vertical direction and water moving in the horizontal direction. Then the application of gelled polymer technology to create a barrier to contaminant transport in soils is 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 function of shear rate. They show low viscosity at high shear rate making the injection in a porous medium easier, and a high viscosity at low shear rate making the solution motionless after the injection. Gelation time may be instantaneous or on the order of weeks depending on the crosslinking agent adopted and its concenstration. 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 the injection of the xanthan solution. If Cr(III) is the crosslinking agent the gelation occurs in a range from 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.