MT3D

Criterion	Explanation
General Description	Subsurface simulation of saturated zone solute transport. Uses output from MODFLOW to solve convective-dispersion equation.
Model Domain	Subsurface saturated zone
Developer	U.S. Geological Survey (USGS)
Hardware computing requirements	Used on personal computers running various versions of the Microsoft Windows operating system. It is recommended to have 2 GB of RAM available to hold all required data. If there is insufficient RAM to run the model, then MT3D-USGS will not initiate the beginning of the simulation.
Code language	FORTRAN 90
Original application	MT3D-USGS is an updated release of the groundwater solute transport code MT3DMS. The code now simulates unsaturated-zone transport and transport within streams and lakes, including solute exchange with connected groundwater. Other capabilities include: Routes a solute through dry cells that may occur in the Newton-Raphson formulation of MODFLOW (BTN Package) Simulates interspecies reactions and parent-daughter chain reactions (RCT Package) Simulates solute retardation and decay Simulates dynamic recirculation with or without treatment for combinations of wells Backward compatibility with existing MT3DMS models is assured.
Public/proprietary and cost	Public; No cost
Physically or empirically based	Physically based
Mathematical methods used	MT3D-USGS solves an advection-dispersion-reaction in a groundwater flow system under generalized hydrogeologic conditions. The code implements a corrected formulation of the transient storage term. New improvements in the code include: Partitioning coefficient (Kd) within mobile and immobile domains are separately specified; Concentrations may be prescribed to the top-most active layer; The change in mass storage owing to the change in water volume now appears as its own budget item in the global mass balance summary; Hydrocarbon Spill-Source Package (HSS) mass loading zones are defined using regular and irregular polygons, in addition to the currently supported circular zones; Absolute minimum thickness can be specified, rather than just using the default percent minimum thickness in dry-cell circumstances.
Input data requirements	MT3D-USGS will not work if a flow-transport link file has not first been generated by MODFLOW-2005 (Harbaugh, 2005) or MODFLOW-NWT. The data arrays in MT3D-USGS are dynamically allocated, so models are not limited by hard-coded array limits. The NAME file contains the names of most input and output files used in a model simulation and controls the parts of the model program that are active. This contains variables including the many budget, transport, and reaction packages. Files such as those used for input of concentrations saved in a previous simulation as the initial condition for a continuation run are read in as binary (unformatted) files. Files such as those used to save formatted concentrations at observation points and mass budget summaries, or for input data from files that are separate from the primary package input files, are input as text files.
Outputs	An output listing file is required for every simulation. Output can be saved for the (binary) concentration file, the formatted concentration observation file, the formatted mass budget summary file, and the model configuration file. Optional CTO file (ASCII) contains a well-by-well printout of the mass balance related to the CTS mass budget package.
Pre-processing and post-processing tools	Visual MODFLOW (Waterloo Hydrogeologic), Groundwater Vistas (Rockware), USGS Model Muse and Model Viewer
Representation of uncertainty	The model does not have built-in uncertainty representation. This can be assessed for each specific case using sensitivity analysis.
Prevalence	Several scientific publications have described the use of MT3D. In the Delta, Deverel et al. (2017) used MT3D coupled with MODFLOW to simulate DOC transport on Twitchell Island.
Ease of use for public entities	There are no restrictions for use. Model files can be accessed at: https://water.usgs.gov/ogw/mt3d-usgs/
Ease of obtaining information and availability of technical support	User guides and example problems available. There is limited support for correcting bugs and clarification of how MT3D-USGS is intended to work. Vivek Bedekar (vivekb@sspa.com) S.S. Papadopulos & Associates, Inc. 7944 Wisconsin Avenue Bethesda, MD 20814 Eric Morway (emorway@usgs.gov) U.S. Geological Survey 2730 N. Deer Run Road Carson City, NV 89701
Source code availability	Source code available via https://water.usgs.gov/ogw/mt3d-usgs/
Status of model development	Developed and available for use.
Challenges for Integration	For integration with surface water modeling, temporal and spatial scales and calculations associated with MODFLOW modeling are different that those used for surface water models. See challenges associated with MODFLOW. MT3D used for simulation of DOC transport and loads on Delta islands.

References

Bedekar, V., Morway, E.D., Langevin, C.D., and Tonkin, M., 2016, MT3D-USGS version 1: A U.S. Geological Survey release of MT3DMS updated with new and expanded transport capabilities for use with MODFLOW: U.S. Geological Survey Techniques and Methods 6-A53, 69 p., http://dx.doi.org/10.3133/tm6A53.

Deverel, S. J, Leighton, D. A, Lucero, C., & 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), https://escholarship.org/uc/item/4q340190.

Harbaugh, A.W., 2005, MODFLOW-2005: The U.S. Geological Survey Modular Ground-water Model–the Ground-water Flow Process: U.S. Geological Survey Techniques and Methods 6-A16, p. 253. Available online at http://water.usgs.gov/ogw/modflow/MODFLOW.html.

See https://water.usgs.gov/ogw/mt3d-usgs/ for an overview of MT3D-USGS, as well as various downloads.

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