SESOIL Soil Input

Parameters

The soil input file contains information on physical properties of the soil. These properties are used by the SESOIL hydrologic and pollutant cycle sub- models. Values for these parameters are typically obtained as part of the site investigation or can be estimated based on soil type. Intrinsic Permeability Permeability is a measure of the rate at which water can flow through the soil. SESOIL uses intrinsic permeability in cm 2 . Permeability in cm/sec can be converted to intrinsic permeability by multiplying by 1.0E-5 cm-sec. Soil permeabilities are typically based on laboratory analysis. Depending on specific site conditions it can be based on groundwater permeability measurements. At other locations it may be established based on soil type. Permeability in the soil input file is applied to the entire soil column. Varying permeabilities with depth can be entered in the SESOIL application input tab. Organic Carbon Content The organic carbon content is defined as the percent of organic carbon of the soil. This is one of the most important site-specific parameters and care should be taken as to which analytical method should be used. The soil input file contains the percent organic carbon content of the uppermost soil layer. Values for organic carbon content in the lower layers can be established in the SESOIL application tab. Soil Bulk Density Bulk density is the amount of mass per unit volume of dry soil in g/cm 3 . SESOIL uses this soil input value for the entire column and there are no provisions for varying bulk densities with depth. Effective Porosity Effective porosity is the fraction of interconnected pore space to the total volume of the soil. This parameter is difficult to measure and is typically estimated based on soil type. Default values can be found in the SEVIEW User’s Guide and help documentation. Porosity in the soil input file is applied to the entire soil column and there are no provisions for varying values with depth. Soil Pore Disconnectedness Index It seems that all vadose zone models have at least one unusual input parameter. The soil pore disconnectedness index is perhaps the most unusual of all of the SESOIL input parameters. This parameter deals with wetting and drying fronts in the soil column associated with precipitation events. As such the soil pore disconnectedness index can have a strong influence on the movement of soil moisture and thus the fate of contaminants. Cation Exchange Capacity The cation exchange capacity is a measure of the number of positively charged cations that can be adsorbed to a given volume of soil. It is typically reported in milliequivalents per 100 grams of soil. SESOIL uses the cation exchange capacity along with the chemical valence to simulate the sorption of metals to soil. Information entered in the soil input file is used to establish the cation exchange capacity of the uppermost soil layer. Relative values for lower soil layers can be established in the SESOIL application tab. The cation exchange capacity is only active in SESOIL if a non-zero value is entered for the chemical valance in the chemical input file. Freundlich Exponent The Freundlich exponent deals with how soil sorption varies with increasing contaminant load. At low concentrations sorption is linear. However, as contaminant load is increased sorption decreases, eventually the soil becomes saturated. The Freundlich exponent is used to define how chemical sorption will respond as load is increased. Given that most residual contaminant concentrations are significantly below soil saturation limits, sorption is assumed to be linear (i.e. the Freundlich exponent is 1.0). The Freundlich exponent value in the SESOIL soil input file is applied to the upper most soil layer. Relative values for the Freundlich exponent in lower layers are entered in the SESOIL application input tab.