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RISKPRO'S SESOIL for Windows User's Guide where ' Jw,z = infiltration rate at depth z, which will be,the boundary between two major layers (cm/s) G = groundwater runoff (recharge) (cm/s) ' I = infiltration at surface (cm/s) d, = depth of soil column below depth z (cm) d = depth of soil column from surface to groundwater table (cm) ' KZ = intrinsic permeability defined by Eq (3) (cm2) k, = the vertically-averaged permeability for layer i (cm2), is computed using Eq (3), except d in the numerator of Eq (3) is the sum of the layer depths above depth z and the summation in the denominator is from layer 1 to layer i - The user is allowed two options for loading of a pollutant (1) a spill loading where all the ' pollutant mass is entered at the soil surface in the first time step of the month when the loading takes place, or (2) a steady application where the pollutant load is distributed evenly for each time step during the month at which the loading is specified Option (1) allows loading at the ' soil surface only (layer 1; sublayer 1), whereas option (2) will allow loading in one or more of the four major layers If sublayers are specified, the loading will always be entered into the fir (top) sublayer of the-major layer Thus, while pollutant can be loaded in each of the four major ' layers, pollutant can not be loaded into each sublayer of a major layer to get a specific initial concentration distribution for the major layer However, the new SESOIL model-allows the - initial concentrations to be specified for any sublayer of the major layers This new featu"A significantly improves the current version of SESOIL - r The initial concentration is optional When the initial concentration is selected, SESOIL i coriverts the initial concentration intora-total pollutant mass first. Then it applies the total mass _ to the first time step-of the month in which the initial mass (loading) takes place, at the sublayer ' where the initial concentration is specified If there is a spill loading or if the pollutant is entered as a steady application in layer 1 (sublayer ' 1), then the depth of the pollutant front is calculated using Eq (I1) starting from the surface If a steady loading is specified in layers 2, 3, and/or 4, then the depth of the pollutant front is assumed to begin at the middle of the lowest layer at which the pollutant is loaded (sublayer 1 ' of that layer if sublayers are included) and Eq (11) is used to compute the depth of the pollutant front from that point -If initial concentrations are specified, the depth of the pollutant front is assumed to begin at the middle of the lower layer where the total mass is applied, regardless of ' the type of the pollutant load. If both the pollutant loading and the initial concentration are used, the pollutant depth will start from whichever has the larger initial depth Table 3 2 summarizes the pollutant loading and initial concentration characteristics used in SESOIL Once the initial ' pollutant front is determined, Eq (11) is used to compute the depth of the pollutant front downward. Subsequently, the pollutant is not allowed to enter a layer (sublayer) until the depth ' Page 22 ' 1