STANMOD

Criterion	Explanation
General Description	Analytical solution to the subsurface convective-diffusion equation for solute transport
Model Domain	Soil and groundwater
Developer	United States Department of Agriculture (USDA)
Hardware computing requirements	For use on Windows machines
Code language	All computational programs are written in FORTRAN, and the graphical interface is in MS Visual C++.
Original application	A Windows-based software package for simulating solute transport in porous media using analytical solutions of the convection-dispersion equation. The suite of analytical models includes models for one-dimensional and multi-dimensional transport.
Public/proprietary and cost	Public; No cost
Physically or empirically based	Physically based.
Mathematical methods used	STANMOD includes several models: The 3DADE model solves the direct problem (i.e., the concentration is calculated as a function of time and space for specified model parameters), and the indirect (inverse) problem in which the program estimates selected parameters by fitting one of the analytical solutions to specified experimental data. In the N3DADE code, analytical solutions for three-dimensional equilibrium solute transport in the subsurface pertain to selected cases of three-dimensional solute transport during steady, unidirectional water flow in porous media having uniform flow properties. Solute transport terms in the equation are: Solute movement by convection Solute movement by dispersion Solute retardation First-order decay Zero-order production STNAMOD uses the analytical solutions to the one-dimensional convective dispersion equation described in Toride et al (1993).
Input data requirements	User creates input data through the Project Manager module. New projects are given a name and assigned to a Workspace (any existing, accessible subdirectory). Input data requirements include groundwater flow related parameters (hydraulic conductivity, storativity), and solute transport related parameters (dispersitivity, porosity, initial pore water concentration, adsorption-related and decay- and production-related parameters).
Outputs	The post-processing unit consists of simple x-y plots for graphical presentation of the results and a dialog window that displays an ASCII output file.
Pre-processing and post-processing tools	ASCII text outputs can easily be brought into Excel.
Representation of uncertainty	The model does not have built-in uncertainty representation. This can be assessed for each specific case using sensitivity analysis.
Prevalence	Widely used for studying vadose zone flow and transport processes, including for agricultural application. STANMOD has used in the Delta to simulate DOC transport in Twitchell Island cores (Deverel et al. 2017).
Ease of use for public entities	Readily available and easy to use
Ease of obtaining information and availability of technical support	Support for problems with the model code, or suggestions for improvement can be submitted to: U. S. Salinity Laboratory USDA, ARS 450 West Big Springs Road Riverside, CA 92507 E-mail: jsimunek@ussl.ars.usda.gov, rvang@ussl.ars.usda.gov
Source code availability	Source code is not readily available. The executable file is available at: https://www.ars.usda.gov/research/software/download/?softwareid=102&modecode=20-36-05-00
Status of model development	Version 2.0 completed for use in 2000
Challenges for integration	STANMOD is a one-dimensional model that is limited in its ability to simulate transient flow conditions. It was previously used to simulate DOC transport in Delta organic-soil column laboratory experiments.

References

Toride, N., Leu, F.J, and Van Genuchten, M.T., 1993, A comprehensive set of analytical solutions for non-equilibrium solute transport with first order decay and zero-order production. Water Resources Research, 29, 2167-2182.

Deverel, S. J, Leighton, D. A, Lucero, C., and Ingrum, T., 2017, Simulation of Subsidence Mitigation Effects on Island Drain Flow, Seepage, and Organic Carbon Loads on Subsided Islands Sacramento–San Joaquin Delta. San Francisco Estuary and Watershed Science, 15(4). Retrieved from https://escholarship.org/uc/item/4q34019.

Simunek, J., Van Genuchten, M.T., Sejna, M. Toride, N. and Leij, F. J., 1999, The STANMOD Computer Software for Evaluating Solute Transport in Porous Media Using Analytical Solutions of Convection-Dispersion Equation, U. S. Salinity Laboratory, Agricultural Research Service, U. S. Department of Agriculture, Riverside, California.

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