dimensional, compartmental, dynamic transport
equilibrium concentration of chemical spe-
and fate model. The model simulates daily
cies over a series of monthly or yearly steps.
changes in chemical concentrations on a spill
3. Pollutant transport takes place in the unsatu-
site's soil and vegetation, as well as losses of
rated soil zone.
chemicals attributable to volatilization, surface
SESOIL input parameters
runoffsoil erosion and leaching to groundwater.
SESOIL has options for annual or monthly sim-
Vertical And Lateral Organic Redistribution
ulations. The annual simulations need annual cli-
(VALOR), a two-dimensional numerical model
matic data and monthly simulations require
for immiscible multiphase fluid flow in subsur-
monthly input data. The annual simulation op-
face systems, was developed by Abriola et al.
tion is not available in the new RISKPRO system;
(1992). VALOR solves only flow (pressure) equa-
therefore, it is not included in this report with the
tions for different phases of air, water and organic
exception of the hydrological cycle, which imple-
liquids; however, MOFAT solves both flow and
ments the annual algorithm. The monthly input
mass transport (concentration) equations.
data are grouped into four types: climate data,
soil data, chemical data and initial chemical dis-
SESOIL EVALUATION
tribution in the soil. The user must supply 57 in-
put variables to run the model (Ladwig et al.
SESOIL processes
1993): 12 monthly input values are required for 33
SESOIL simulates the major processes that can
of the parameters. In the execution file, 8 addi-
affect pollutant transport in the unsaturated
tional parameters are required. The washload in-
zone, including moisture movement, volatiliza-
put file was not used at the Fort Greely site; there-
tion and vapor phase diffusion, adsorption, and
fore, a discussion of the sediment module is not
chemical as well as biological degradation (Lad-
included. Details of input variables for the four
wig et al. 1993). The hydrological cycle compo-
categories are as follows.
nent is based on the theory of Eagelson (1978) that
uses a statistical approach to water balance calcu-
Climate data
lations for estimating one-dimensional soil-water
1. Average monthly temperature.
movement. Parameters considered in the hydro-
2. Average monthly fraction of cloud cover.
logic cycle are rainfall, surface runoff, infiltration,
3. Average monthly relative humidity.
soil-water content, evapotranspiration and
4. Average monthly shortwave albedo.
groundwater runoff. The sediment cycle relates
5. Monthly precipitation depth.
to sediment washload as a result of rainstorms
6. Mean storm duration.
(i.e., soil erosion from surface runoff). To incorpo-
7. Number of storms.
rate the effect of washload, the sediment module
8. Latitude.
uses a combined statistical and deterministic ap-
9. Mean length of rain period.
proach. The pollutant fate cycle includes convec-
10. Average daily evapotranspiration rate.
tive transport, volatilization, adsorptiondesorp-
Soil data
tion, chemical degradationdecay, biological
1. Description of soil type.
transformation, hydrolysis, photolysis, oxidation
2. Soil bulk density.
and complexation with metals. This module uses
3. Intrinsic permeability.
a deterministic approach with analytical equa-
4. Disconnectedness index.
tions describing chemical and biological process-
5. Effective soil porosity.
es that affect contaminant transport. Details of
6. Organic carbon content.
these cycles, along with the transport equations,
7. Freundlich exponent.
are given in the New SESOIL User's Guide (Hatrick
8. Cation exchange capacity.
et al. 1993).
Chemical data
1. Description of the compound.
SESOIL assumptions
The SESOIL model is based on three assump-
2. Solubility in water.
tions:
3. Diffusion coefficient in air.
1. Pollutant concentrations in all phases and in
4. Henry's Law constant.
all compartments of the soil system are at
5. Adsorption coefficient on organic carbon.
equilibrium at all times.
6. Overall adsorption coefficient.
2. The law of mass conservation determines the
7. Molecular weight of the compound.
3
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