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in the physical parameters of the site. The simulation data apply to the entire site, brit can be modified.or changed between simulations. The following is a list of the data entered for each polygon;, i • Thnestep -total time of simulation, profile and output intervals in years. • Area—area of polygons)in square feet. • Vertical cell dimension—height of cell within the polygon in feet. • ..Initial contarnimant concentration—contamination'in µg/kg and is specified.for each cell. • Recharge pate—velocity of water movement through-the vaddse zone.(ftlyear);in the vadose zone.,the hydraulic-conductivity of the soil'is an increasing ftinction of i the water content of the soil. Hense,the groundwater recharge rate should be �r equal to or lower than the hydraulic conductivity of the soil within.the modeled area. The parameter is difficult to estimate'and can vary over time. The parameter has a strong effect on calculated data and is recommended that'a range-of values be employed. • Dry bulk density- mass of dry soil relative to the bulk volume of soil(g/cm3). The parameter ranges based on the soil types and.can-have'a major erect the calculated data. • Effective porosity—the volume of void space within the soil that is potentially fillable with water(%).. The parameter,ranges based`on the soil types and has a riiinor effect on the calculated data: - • Volumetric water content—.water content of the soil in percent total volume. This parameter is assumed'constant in time and space, However,this rarely occurs -in nature. The value can neither exceed the porosity of the.soil nor be lower than the irreducible soil water.content. • Soil organic carbon content—fraction of organic material in the soil. The �¢7 parameter defines the amount of potential absorptive sites for the contaminant in the solid phase. The value can be determined from laboratory analyses or is documented in some soil descriptions of the,Soil Conservation Service. Generic e values based on soil of different textures are in published data. • Concentration of recharge water--contaminant concentration(mg(L): If the recharge..water is derived from precipitation the value will typically be set to zero. 4