Software needed to run (1) flow model, (2) particle tracking, and (3) Particle-tracking analysis
(1) MODFLOW-2005, MODFLOW-NWT, MODFLOW-FMP, or GSFLOW (http://water.usgs.gov/nrp/gwsoftware/modflow.html)
(2) MODPATH (Version 6.0.01) (http://water.usgs.gov/ogw/modpath/) or 
    MODPATH-LGR for multi-grid applications (Version 1.0) (http://water.usgs.gov/nrp/gwsoftware/ModpathLgr/ModpathLgr.html)
(3) MODPATH-OBS (Version 1.0)