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i <br /> RISKPRO'S SESOIL for Windows User's Guide <br /> Originally, only the advective velocity was used in SESOIL to determine the depth the pollutant <br /> reached dunng a time step. The depth (D) was calculated as <br /> D = JWtC (10) <br /> e <br /> where- <br /> Jw = water velocity (cm/s) <br /> t. = advection time (s) <br /> 0 = soil water content (cm3/cm3) <br /> This approach allows all chemicals to reach the groundwater at the same time, regardless of their <br /> Ichemical sorption characteristics. To account for retardation, SESOIL now uses the following <br /> equation to calculate the depth reached by a chemical with a linear equilibrium partitioning <br /> between its vapor, liquid, and adsorbed phases (Jury et al , 1984)- <br /> D = JW tc <br /> + + fa H (11) <br /> 9 PbKd R (T+273) <br /> SESOIL calculates the flux Ja, for each layer using the infiltration rate and groundwater runoff <br /> (recharge) rate computed by the hydrologic cycle, and the depths and permeabilities input by the <br /> user. Note that a different permeability can be input for each of the four major soil layers. <br /> I While the hydrologic cycle will use the weighted mean average of layer permeabiliries according <br /> to Eq (3), the pollutant cycle does take into account the separate permeability for each layer in <br /> computing J,,, at the layer boundaries according to the following equation <br /> JwIZ _ [G+(I--G)(a1)] (kt ) (12) <br /> d Kz <br /> Page 21 <br />