S.S. Papadopulos and Assoc. Inc., in collaboration with the University of Waterloo, has developed the most powerful particle tracking program for MODFLOW and MODFLOW-USG.

​Key Features

  • The Waterloo method 
    • The most powerful algorithm available for MODFLOW and MODFLOW-USG.
    • Semi-analytical solution, similar to the Pollock method, applicable to arbitrary cell geometries.
  • Supports all cell geometries available to MODFLOW-USG
    • Including nested grids, quadpatch and quadtree, Voronoi, and triangular.
  • Implicit Weak-Sink Support
    • Intra-cell analytic solutions to accurately track particles in the vicinity of a pumping well.


  • Work in global coordinates
    • Provide particle starting locations and track and get results in real-world coordinates.
    • Plot in your GIS program of choice without converting coordinates.
  • High-order Runge-Kutta scheme
    • Particles are tracked in the x and y-direction using the fourth-order Runge-Kutta scheme from the original Path3D.
    • Adaptive time-stepping. Time step size is adjusted automatically to account for curvature in the flow field.
    • An Euler tracking option is also available.
  • Based on the MODPATH6 platform

Our exclusive tracking algorithm will track particles to the well, not the cell boundary.
Download the software and see the manual for more details.
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SSP&A's software is provided "AS IS", without warranty of any kind, including, without limitation, the warranties of merchantability, fitness for a particular purpose and non-infringement. We request only that application of the software and production of results using the code is accompanied by a suitable acknowledgment. The entire risk and responsibility as to the quality and performance of the Software is borne by the user. SSP&A disclaims all other warranties.