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t <br /> F <br /> Biotic processes controlling contaminant transport are similarly affected by both the subsurface <br /> properties, including the presence of microorganisms, nutrients and oxygen and the contaminant <br /> properties of concentration and biochemical oxygen demand(Borden and Bedient, 1986). <br /> 5_3 SMOIL Fate and Trans ort In ut Parameters <br /> Smith Environmental used the ra computer ram SESOIL <br /> p program to simulate the fate and transport of <br /> the residual soil contamination remaining under the Police Building. The input parameters for <br /> the Stockton Police Facility vertical transport model are summarized in Table 5. The input <br /> parameters discussed below are grou `ped into five sections: weather; initial soil concentration; <br /> soil profile; soil properties; and, chemical parameters. <br /> 5.3.1 Weather <br /> SESOIL was supplied from General Sciences Corporation with a climatic database for the state <br /> of California. A Stockton weather station "Stockton Disposal PL" is selected because it is the <br /> closest available station to the site (Latitude 37.993 and Longitude 121.333 degrees). . <br /> 5.3.2 Initial Soil Concentrations <br /> For each chemical of interest, benzene, toluene, xylenes and eth lbenzene the highest <br /> Y Y g <br /> concentration found near or in the unexcavated impacted area is specified for input. The <br /> vertical concentration distribution in the impacted thickness is also assumed constant. Using <br /> the highest concentration found in a one dimensional model is more conservative than a more <br /> representative three dimensional model: <br /> 5.3.3 Soil Profile <br /> The impacted zone is estimated to extend from a depth of 3 to 8 feet below the ground surface. <br /> The soils beneath the site are comprised of clay and silt from the surface to 'a depth of <br /> approximately 28 feet, then silt and silty sand from approximately 28 feet to the water table. <br /> The subsurface has been explored to a depth of 55 feet. During the period of investigation, <br /> the depth to;groundwater has ranged from 38 feet to 47 feet below grade. SESOIL permits a <br /> maximum of 4 layers in the computer model. Therefore, the following layers were specified: <br /> Layer No. Thickness Description <br /> 1 3' Clean surface sail <br /> 2 5' Impacted soil layer <br /> I 3 20' Silt and Clay <br /> 4 10' Sift and Sand <br /> w:19436ftq)ortshe R.doc 6 <br /> SKTH <br /> I <br />