BTN: Basic Transport Package Pane

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The BTN: Basic Transport pane is is on the MODFLOW Packages and Programs dialog box under MT3DMS or MT3D-USGS. It is used to specify some of the data for the BTN package in MT3DMS or MT3D-USGS. Some other data for the BTN package are specified in the the MODFLOW Time and MODFLOW Output Control dialog boxes. The BTN package is required in all MT3DMS and MT3D-USGS models.

The comments can be used to record any information. The first two lines will be the heading for the simulation and will be printed in the MT3DMS output file.

MUNIT is the name of unit for mass, such as LB or KG. Note that this names is used for identification purposes only and does not affect the model outcome.

CINACT is the value for indicating an inactive concentration cell (MT3DMS_Active = False). Even if inactive cells are not anticipated in the model, a value for CINACT still must be submitted.

THKMIN is the minimum saturated thickness in a cell, expressed as the decimal fraction of the model layer thickness (DZ) below which the cell is considered inactive. The default value is 0.01 (i.e., 1 percent of the model layer thickness).

The user also defines the names of the Mobile and Immobile chemical species. The names of the chemical species are not part of the MT3DMS or MT3D-USGS input but they are used to identify data sets and output files related to individual chemical species.

“Mobile species” are involved in both transport and reaction while “immobile” species are involved in reaction only. Also, for each species, MT3DMS or MT3D-USGS automatically tracks a sorbed or immobile counterpart if a sorption isotherm or dual-domain mass transfer is specified through the Chemical Reaction Package. Thus, there is no need to define separate “immobile” species to simulate sorption or a dual-domain system. The ability to define separate immobile species is only intended for using MT3DMS or MT3D-USGS with add-on reaction packages.

The initial values for either the mobile or immobile species can be read from a concentration file created by MT3DMS or MT3D-USGS. The data in the file must have the same number of columns, rows, and layers as the model. To use such a file, check the check box in the table next to the chemical species name in the column labeled Use Initial Concentration File and then enter the file name in the column labeled File Name. You can click in the File Name column to display a Select button. Clicking the Select button will allow you to select the file. You will also need to specify the Stress period, Time step, and Transport step of the concentrations that you want to use.