An MT3DMS model can be created in GMS using one of two methods: assigning and editing values directly to the cells of a grid (the grid approach), or by constructing a high level representation of the model using feature objects in the Map module and allowing GMS to automatically assign the values to the cells (the conceptual model approach). For sites with complex source/sink terms and boundary conditions, the conceptual model approach is often the most effective. The conceptual model approach utilizes feature objects in the Map module.
In order to use the conceptual model approach to build an MT3DMS model, the same conceptual model must be used for both the MODFLOW flow model and the MT3DMS transport model. This ensures that there is a proper linkage between the sources/sinks in the conceptual model and the sources/sinks in the grid model.
The following steps are used in setting up a conceptual model and converting the conceptual model to a numerical model:
Construct a MODFLOW conceptual model, create a grid, and convert the conceptual model data to the MODFLOW data defined at the grid cells.
Run the MODFLOW simulation to save the MT3DMS head and flow file.
Return to the Map module. Edit the properties of the Conceptual model to include transport. Assign concentrations to the sources/sinks in the conceptual model where necessary. Also define polygonal zones describing layer data including porosity, longitudinal dispersivity, sorption constants, rate constants, and bulk density.
Select the Map -> MT3DMS command to automatically assign the MT3DMS data to the appropriate cells in the grid.
Related Links:
MT3DMS Interface
Building an MT3DMS Simulation