Finite-Element Method Solution of Non-Fickian Transport in Porous Media: The CTRW-FEM Package.

An exposition is given of a finite-element method (FEM) software package to calculate solutions for the continuous time random walk (CTRW) integro-differential equation for non-Fickian (and Fickian) conservative or reactive transport in disordered media. The solutions encompass one-dimensional/two-dimensional (1D/2D) breakthrough curves and spatial concentration profiles for general geometry and grid. The velocity field, used as input to the 2D solutions, may also be calculated by applying a compatible Darcy flow 2D solver. The software enables both "forward" modeling (1D/2D) and "inverse" (best-fit) modeling (1D) of experimental data. Various inlet and outlet boundary conditions are implemented. The CTRW-FEM Package is freely downloadable and contains a User's Guide, source and executable files, and accompanying files with easy-to-use format, including descriptions of input/output files and pre- and post-processing. Several examples are provided to clearly demonstrate how to work with the CTRW-FEM Package in many typical analyses. The CTRW-FEM Package also allows users to adapt the software to specific needs, such as, for example, first- and second-order chemical reactions.