The chemical input file contains information describing the chemical and physical properties of the contaminant released or applied to the soil column. This information includes water solubility, air diffusion coefficient, Henry’s Law constant, organic carbon adsorption coefficient, soil partition coefficient, molecular weight, valence of the compound, acid, base and neutral hydrolysis rate constants, liquid and solid phase biodegradation rates, ligand stability constant, moles ligand per mole compound, and the molecular weight of the ligand. A copy of the chemical input screen tab and a description of the input parameters are presented below.
The following parameter descriptions are provided as a guideline for each of the chemical parameters used in SESOIL.
The following descriptions also apply to the chemical database. The chemical
database is opened by clicking on the command displayed
in the SESOIL chemical input screen tab. A copy of the chemical database screen is presented below.
As you can see this window looks very much like the input screen with the addition of the chemical, CAS number and formula fields. To copy the data to the SESOIL chemical input file move to the desired chemical and click on the
command and close the database window. If you do not want to update the SESOIL chemical file simply close the window.
Parameter Description of the Chemical Data Set / Chemical Name SESOIL Variable TITLE
Description Description used to identify the chemical data set. Limited to a maximum of 48 characters in length.
Parameter Water Solubility
Units (mg/L)
SESOIL Variable SL
Description The solubility of the compound in water at 25 C. Source of Data Chemical reference literature.
SESOIL requires a water solubility value for the chemical. If the water solubility is unknown and migration to groundwater is the concern, then an estimated value that is somewhat high should be used. This will ensure that the estimates of chemical of chemical leaching are conservative.
Parameter Air Diffusion Coefficient
Units cm2/sec
SESOIL Variable DA
Description The diffusion coefficient in air, used by SESOIL to calculate volatilization.
Source of Data Chemical reference literature, or air diffusion coefficient can be estimated using the following relationship:
DA
DA
MWT
MWT
'
'
where:
Parameter Description
DA Air diffusion coefficient of the current compound, DA' A diffusion coefficient for a reference compound, MWT' Molecular weight of the reference compound, and
MWT Molecular weight of the current compound.
The diffusion coefficient (0.083 cm2/sec) and molecular weight
(131.5 g/mole) for trichloroethylene can be used as the reference compound.
Parameter Henry’s Law Constant
Units M3-atm/mol
SESOIL Variable H
Description Dimensional form of Henry's Law constant (m3-atm/mole), used in Equations (A7), (A11), and (A13) in Appendix A.
Source of Data Chemical reference literature.
Parameter Organic Carbon Adsorption Coefficient, Koc
Units (g/g)/( g/ml) SESOIL Variable KOC
Description The adsorption coefficient of the compound on organic carbon. If the adsorption coefficient on the soil Kd, is used, a zero should be entered for organic carbon adsorption coefficient, as it will not be used. Source of Data Chemical reference literature.
Values entered for Koc, soil partition coefficient (K), liquid phase biodegradation
rate, and solid phase biodegradation rate are for the uppermost soil layer and are used as a reference point for the other layers. The layer-specific ratios can be specified in the application file (see Section 6.7).
Parameter Distribution Coefficient, Kd
Units (g/g)/( g/ml) SESOIL Variable K
Description The distribution coefficient of the compound on soil. If a non-zero value is entered for the soil partition coefficient (Kd), SESOIL will use this value as the adsorption coefficient. If a zero is entered for the distribution coefficient, SESOIL will calculate Kd by multiplying the organic carbon adsorption coefficient (Koc) times the soil organic carbon content, (OC in the soil input file) see Appendix A, Section A2.5.4.
Source of Data Chemical reference literature.
Adsorption in SESOIL can be represented either by the overall distribution coefficient (K), which is often labeled Kd in the literature, or by the organic
carbon:water partitioning coefficient, Koc. If a value for the overall distribution
coefficient is unknown, this parameter should be entered as zero. In this case, SESOIL uses the product of Koc and the organic carbon fraction to produce an
estimated value for the distribution coefficient (K). If the user enters a measured value for the distribution coefficient, SESOIL will not perform the estimation. Values entered for distribution coefficient (K) and organic carbon adsorption coefficient (KOC) apply to the uppermost soil layer; layer-specific ratios are
entered in the application file.
Parameter Molecular Weight
Units g/mol
SESOIL Variable MWT
Description The molecular weight of the compound. Source of Data Chemical reference literature.
Molecular weight is only used if the complexation or cation exchange algorithms are utilized.
Parameter Valence of the Compound
Units g/mol
SESOIL Variable VAL
Description The valence of the compound used to calculate cation exchange with soil. A positive integer number should be entered without a sign.
Source of Data Chemical reference literature.
VAL is used only if the cation exchange algorithm is used.
Parameter Neutral Hydrolysis Rate Constant
Units L/mol/day
SESOIL Variable KNH
Description The neutral hydrolysis rate constant (L/mol/day). Source of Data Chemical reference literature.
Parameter Base Hydrolysis Rate Constant
Units L/mol/day
SESOIL Variable KBH
Description The base hydrolysis rate constant (L/mol/day). Source of Data Chemical reference literature.
Parameter Acid Hydrolysis Rate Constant
Units l/mol/day
SESOIL Variable KAH
Description The acid hydrolysis rate constant (L/mol/day). Source of Data Chemical reference literature.
Parameter Liquid Phase Biodegradation Rate
Units l/day
Description The biodegradation rate of the compound in the liquid phase. Source of Data Chemical reference literature.
Parameter Solid Phase Biodegradation Rate
Units l/day
SESOIL Variable KDES
Description The biodegradation rate of the compound in the solid phase. Source of Data Chemical reference literature.
Parameter Ligand Stability (Dissociation) Constant
Units Dimensionless
SESOIL Variable SK
Description The stability (dissociation) constant of the compound/ligand complex. A zero should be entered if a ligand compound is not used. Source of Data Chemical reference literature.
Parameter Moles Ligand per Mole Compound
Units Dimensionless
SESOIL Variable B
Description The number of moles of ligand per mole of compound complexed. A zero should be entered if a ligand compound is not used.
Source of Data Chemical reference literature. Parameter Water Diffusion Coefficient
Units cm2/sec
SESOIL Variable DW
Description Water diffusion coefficient. Source of Data Chemical-specific.
SEVIEW Link The water diffusion coefficient is not used by SESOIL, however it is passed to AT123D.
Units g/mol SESOIL Variable MWTLIG
Description The molecular weight of the ligand (g/mole). A zero should be entered if a ligand compound is not used.
Source of Data Chemical reference literature.
Additional processes for handling the binding of a contaminant to soil
constituents are included in the cation exchange and complexation options. The molecular weight and valence of the contaminant are used in the cation
exchange calculations. Complexation estimation requires the contaminant's molecular weight, the molecular weight of the ligand participating in the complex, the moles of ligand per mole of contaminant in the complex, and the stability constant of the contaminant/ligand complex.
Cation exchange and complexation are primarily used for metals. Values for these parameters can be set to zero for most other applications.