Model for Long-Term Pollutant Fate and Migration

SESOIL is a seasonal compartment model which simulates long-term pollutant fate and migration in the unsaturated soil zone. The model describes the following components of a user-specified soil column which extends from the ground surface to the ground-water table.

SESOIL estimates all of the above components on a monthly basis for up to 999 years of simulation time. It can be used to estimate the average concentrations in ground water. The soil column may be composed of up to four layers, each layer having different soil properties which affect the pollutant fate. In addition, each soil layer may be subdivided into a maximum of 10 sublayers in order to provide enhanced resolution of pollutant fate and migration in the soil column. The following pollutant fate processes are accounted for: Volatilization, Adsorption, Cation Exchange, Biodegradation, Hydrolysis and Complexation.

SESOIL can be used as a screening tool in performing exposure assessments. EPA uses the model to predict the behavior of pollutants in soil compartments for analyzing and prioritizing chemical exposures.

SESOIL accepts time-varying pollutant loading. For example, it is able to simulate chemical releases to soil from a variety of sources such as landfill disposal, accidental leaks, agricultural applications, leaking underground storage tanks, or deposition from the atmosphere. Other potential applications include long-term leaching studies from waste disposal sites, pesticide and sediment transport on watersheds, studies of hydrologic cycles and water balances of soil compartments. SESOIL can also be used to estimate the effects of various site management/ design strategies on pollutant distributions and concentrations in the environment.



The Climate Database consists of 3,225 weather stations throughout the continental U.S. is available for purchase by state and the entire U.S. The data originally came from the National Climatic Data Center (NCDC) of the National Oceanographic and Atmospheric Administration (NOAA). It consists of all the monthly statistical parameters required by SESOIL (rainfall information from hourly precipitation stations and evaporation-related information from monthly state climatic division means) accessed by latitude/longitude coordinates of the U.S. An additional variable, ALBEDO, which represents the monthly shortwave albedo of the land surface is also incorporated into the data.
The Zip Code Database contains the zip codes and the corresponding latitude/longitude coordinates for all of the U.S.
The SOILS-5 Database provides soil information required by SESOIL for over 14,000 soil series across the U.S. and comes from the USDA Soil Conservation Service's (SCS) Soils-5 database. Single variables, i.e., bulk density of the soil, effective porosity, and layer-dependent variables, i.e., thickness, intrinsic permeability, are retrieved from the database. Included with SESOIL are eight measured property files for the most commonly-modeled chemicals - Benzene, 1,1,1-Trichloroethylene, Trichloroethylene, Naphthalene, Ethylbenzene Toluene, Hexachlorobenzene, and Tetrachloroethylene.
SESOIL creates an output file which contains monthly results for hydrologic cycle components, pollutant mass distribution, and pollutant concentration distribution for each layer or sublayer. SESOIL also generates a SESOIL-AT123D link file which contains pollutant mass-to-ground-water leachate quantities entering the aquifer from the unsaturated zone. This file can be used as input to the AT123D ground-water model in RISKPRO. Within RISKPRO, line graphs of "concentration vs time" at any specified depth within the unsaturated zone may be created from SESOIL results. " Pollutant-front-depth vs. time" may also be created.

TABLE 1 Input Parameters for SESOIL

CLIMATE Evapotranspiration-Monthly
Air temperature
Cloud cover fraction
Relative humidity
Short wave albedo
Rainfall Statistics-Monthly
Mean storm duration
Rainfall depth
Number of storms per month
Length of rainy season within month
All climatic parameters can be obtained from the RISKPRO Climate Database
SOILBulk density of the soil
Intrinsic permeability
Soil disconnectedness index
Effective porosity
Organic carbon content
Cation exchange coefficient
Freundlich equation exponent
All soil parameters except Freundlich exponent can be obtained from the RISKPRO Soils Database
Solubility in water
Diffusion coefficient in air
Henry's Law Constant
Adsorption coefficient on organic carbon
Adsorption coefficient in soil
Molecular weight; Valence
Hydrolysis rates (neutral, base, acid)
Biodegradation rates (liquid and soil phases)
Ligand (optional)
Ligand stability constant
Moles. ligand per mole. compound
Molecular weight of ligand
Common Chemical Files are available for:

1,1,1,- Trichloroethylene
APPLICATION Compartment Specifications
Number of soil layers and number of sublayers for each layer
Application area and latitude of site
Layer-Dependent Soil Properties
Biodegradation rate ratios for lower layers
Organic carbon content ratios for lower layers
Cation exchange coefficient ratios for lower layers
Pollutant Loading
Instantaneous or continuous
Initial pollutant concentration for any sublayer
Monthly loading rates and miscellaneous parameters
Pollutant loading for the major layer
Pollutant transformed/removed for the major layer
Pollutant concentration in rain
Ligand input mass
Volatilization index
Surface runoff participation index
Groundwater Parameters
Saturated hydraulic conductivity, horizontal gradient, thickness, and width.
Layer-dependent parameters can be obtained from the RISKPRO Soil Database
Intrinsic permeability
Organic carbon content
WASHLOAD (Optional)Washload area
Percent of silt, sand, and clay
Slope length; Average land slope
Soil erodibility factor and soil loss ratio
Contouring factor and Manning's coefficient
Erodibility factor can be obtained from the RISKPRO Soils Database


PC 486/Pentium running Microsoft Windows.

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