MT3D has a modular structure similar to MODFLOW. If your MODFLOW is not adapted to write output files for MT3D, you can follow the directions in the MT3D module and then recompile MODFLOW.

The modules include:

Basic Transport (BTN)

BTN sets up the simulation, specifies initial and boundary conditions, delineates time step size, and controls printout of the simulation results.

Flow Model Interface (FMI)

Reads the contents of an unformatted disk file created by the MODFLOW simulation

Advection (ADV)

Solves the advective portion of the transport either by particle tracking or sets up the coefficient matrix for matrix depending on the selected option.

Dispersion (DSP)

Solves the concentration change due to dispersion explicitly or formulates the coefficient matrix of the dispersion term for the matrix solver.

Sink/Source Mixing (SSM)

Solves the concentration change due to sink/source mixing explicitly or formulates the coefficient matrix of all sink/source terms for the matrix solver.

Chemical Reactions (RCT)

Solves the concentration change due to reaction explicitly or formulates the coefficient matrix of the reaction term for the matrix solver.

Generalized Conjugate Gradient Solver GCG)

Solves the matrix equations resulting from the implicit solution of the transport equation.

Utility (UTL)

Performs basic tasks needed by the other packages, such as input/output control.