Processing ModflowTM is a comprehensive integrated groundwater modeling system that is used by many organizations, such as schools, consulting firms, agencies, and entities of the United Nations. Processing Modflow 8 succeeds Processing Modflow Pro (7.x) and includes the following components: Intuitive graphical user interface to greatly simplify and clarify data input and result visualization processes that work with result files of practically unlimited file size (way greater than 2 GB). 3D finite-difference groundwater model MODFLOW. Supports multiple versions, including MODFLOW-96, MODFLOW-2000, and MODFLOW-2005. Solute transport models MT3DMS (v5.3), MT3D, RT3D (v2.5), and MT3D99 (MT3D99 is sold separately by SSP&A.) Multicomponent reactive transport model PHT3D (v2.0) that incorporates MT3DMS (v5.2) for the simulation of three-dimensional advective-dispersive multi-component transport and the geochemical model PHREEQC-2 (v2.14) for the quantification of reactive processes. Variable-density groundwater flow and multi-species solute and heat transport model SEAWAT (v4.0) . Nonlinear parameter estimation package PEST (v12.0). Supports advanced features such as regularization, truncated singular value decomposition (SVD), and powerful SVD-Assisted Parameter Estimation. Particle-tracking Model PMPATH which uses a semi-analytical particle-tracking scheme similar to MODPATH to calculate the groundwater paths and travel times. Through the interactive graphical modeling environment of PMPATH, the user can place particles and perform particle tracking with just a few mouse clicks.