Well,

Simple software is Groundwater Contour.

Sincerely

There are few contaminate transfer model like MT3DMS, RT3D, PHD3D. It will be advisable to start with MT3DMS.

Thanks

Modflow, Feflow, GMS, Comsol are visual software,

if you know how to use C language, Matlab is good as well.

Sincerely.

Start with the computer program GMS - packages Modflow, MT3D-MS, and so on.

I sincerely appreciate your attention to my question, Thank you everyone for responding.

For a 3-D numerical model, you can model groundwater hydraulics with MODFLOW. Then, that output can be used to model contaminant transport with MT3DMS. Both models are freely available from USGS. However, it is advisable to use a GUI to operate the models. Commercial software for this exists. For example, GroundwaterVistas. The licenses are expensive, though. USGS offers some free operating software (MODELMUSE), but they won't be as easy as commercial GUI (but free!). Check out USGS website: https://water.usgs.gov/nrp/software.php

For light start - PMWin ver. 5.3 freware