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• RESULTS OF MODELING SOIL CONTAMINATION USING LATEST SOIL BORING DATA FOR FORMER REGAL STATION 604, 1.448 N. EL DORADO STREET AND HARDING WAY, STOCKTON, CALIFORNIA. VLEACH The model used to predict the fate of the soil contamination was VLEACH. VLEACH is a numeric model for simulation of vertical water and chemical movement in the vadose zone The following process are simulated: advection, sorption, vapor-phase diffusion and three-phase equilibrium. VLEACH is available from the Center for Subsurface Modeling Support, Robert S. Kerr Environmental Research Laboratory, US EPA, P.O. Box 1198, Ada, OK 74820, send one pre-formatted to the above address with a return disk mailer. VLEACH allows the simulation of a single contaminate in multiple soil polygons . The polygons represent a volume of soil from the surface to ground water over which the soil properties are the same and the contaminate concentration is constant through the horizontal extent of the polygon. The contaminate concentration can be entered in up to one foot vertical intervals. VLEACH requires the following contaminate properties be know or estimated for the contaminate compound fate to be simulated: • Koc The soil-water pardon coefficient, which indicates the relative tendency of a compound to remain dissolved in water or to absorb onto the organic carbon in soil . kh = The Henry' s laws constant, which indicates the partitioning of the compound between the vapor and water phases AS = Aqueous Solubility, how soluble the compound is in water. Da = The free air diffusion coefficient, which indicates how fast the compound will move in air. Compound Koc Kh AS Da ml/g - - mg/1 m'/day n-octane 6800 . 0 140 . 0 . 66 0 . 6 Benzene 97 . 0 0 . 22 1780 . 0 0 . 78 Toluene 140 0 0 30 500 . 0 0 . 72 Ethylbenzene 622 0 0 . 40 150 . 0 0 65 Xylene 522 . 0 0 4 156 . 0 0 . 66 Oxygen 0 75 9 . 06 1 54