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IS SESOIL Fate and Trans ort Input Parameters <br /> Smith Environmental used the computer program SESOIL to simulate the fate and transport of <br /> l 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 grouped into five sections weather, initial soil concentration; <br /> soil profile; soil properties; and, chemical parameters <br /> 5.3.1 Weather <br /> SESOIL was suppled 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 /> Ir For each chemical of interest, benzene, toluene, xylenes and ethylbenzene, the highest <br /> 1 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 /> 1 - 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 Prof le <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 /> Ithe 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 /> Laver Thickness Description <br /> 1 3' Clean surface soil <br /> 2 5' Impacted soil layer <br /> 3 20' Silt and Clay <br /> t_ <br /> 4 10' Silt and Sand <br /> A fat clay exists from approximately 7 feet to 9 feet below grade in the area of interest <br /> (according to soil boring SB2) This very low permeability layer directly below the impacted <br /> area acts as-a natural barrier-to-contaminant-migration" -The-SESOIL model conservatively _ <br /> ignores this natural bamer <br /> I <br /> w\9436$lrgmrts\smd doc b <br /> SMTN <br /> I � <br />