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• Upper boundary condition for vapor--contaminant concentration (mg/L) in the <br /> atmosphere above the soil surface. If the upper boundary of the polygon is <br /> considered impermeable to gas diffusion a negative value is entered. <br /> Lower boundary condition for vapor—contaminant concentration (mg/L)in the <br /> groundwater at the base of the vadose zone. If the lower boundary of the polygon <br /> is considered impermeable to gas diffusion a negative value is entered. <br /> Simulation data will include multiple polygons, time step and the total length of time in the <br /> simulation data. The input parameters are bated on the characteristics of the particular <br /> contaminant. 'The following is a list of input data: <br /> • Organic carbon distribution coefficient(K,,,)—describes the partitioning of the <br /> contaminant with organic carbon in ml/g. The data is obtained through published <br /> reference manuals or obtained from the manufacturer of the compound. <br /> • Henry's constant (X�)—empirically derived constant that describes the liquid-gas <br /> partitioning of the contaminant. It is a function of the solubility and partial vapor <br /> pressure of the contaminant at a given temperature. VLEACH uses the <br /> dimensionless form of Henry's constant. The data is obtained through published <br /> reference manuals or an estimate can be calculated using thefollowing formula: <br /> (Vgpor Pressure—mm Hg) (Molecular weight- moles (40._6.5 <br /> 760 (Solubility—mg/L) <br /> • Nater solubility---water solubility of contaminant in mg/L. <br /> • Free air diffusion coefficient—describes the transfer of the contaminant due to <br /> Brownian motion in the air phase in mZ/day. The data is obtained through <br /> published reference manuals. <br /> 3.3 Other Modeling Considerations <br /> The model was developed to estimate the impact due to the mobilization and migration of <br /> a sorbed organic contaminant. 'However,the model relies heavily on specific properties <br /> inherent to the specified contaminant and the data for any particular compound are not <br /> always readily available. In addition, contaminants_ are often a mixture of compounds or <br /> chemicals whose concentration and properties can also vary. <br /> 3.4 Output Data . <br /> VLEACH output provides information regarding the input parameters,the physical nature <br /> of the vapor, liquid and solid contaminant mass balances in the soil, groundwater impacts <br /> from the contaminant, and the concentration profile of the contaminant within the soil <br /> profile. This information appears in tabular format. The output can also be presented in a <br /> 5 <br /> S <br />