• Extends physical modeling capabilities of MODFLOW for subsurface flow calculations.
• Enhances robustness and efficiency of MODFLOW even for its existing capabilities.
• Seamlessly integrates state-of-the-art, mass conservative, multicomponent contaminant transport capabilities into MODFLOW simulations.
• Dynamic memory allocation permits unlimited problem dimensions.
• Modular structure allows further development of additional simulation capabilities to provide a comprehensive, general purpose simulator within the MODFLOW framework.
• MODFLOW users require negligible training to implement the physics provided by the enhanced modules, due to the use of MODFLOW's input/output structures. Modifications to existing MODFLOW pre- and post- processors to include the enhanced capabilities are, therefore, also minimal.

Benefits of MODFLOW-SURFACT

• Handles complete desaturation and resaturation of grid cells
• Accurate delineation and tracking of water table position, taking into account flow in the unsaturated zone, delayed yield, and vertical flow components
• Automatic and correct redistribution of the total flow rate of a well screened through multiple model layers when the upper cell(s) are pumped dry
• Accommodation of wellbore storage and overpumped wells
• Prevents water table buildup beyond a specified recharge-ponding elevation
• Handling of seepage face boundary conditions
• Adaptive time-stepping schemes automatically adjusts time-step size to the non-linearities of the system to optimize the solution stability
• Robust and efficient Pre-conditioned Conjugate Gradient matrix solver
• Capability of modeling unsaturated water or air movement
• Enhanced Newton-Raphson linearization option increases robustness for unconfined and/or unsaturated flow conditions

• The powerful PCG5 solver¹ add-on is up to 20 times faster than the PCG4 solver thanks to its advanced computational techniques
• The Recharge Package (RSF4) has been modified to include zonal input of recharge with zonal recharge values provided via a separate recharge time-series (RTS) file that is independent of the stress-period setup for varying boundary conditions
• The Evapotranspiration (ET) packages EVT and ETS1 (referred to as ET2 in MODFLOW-SURFACT) have been modified to include zonal input of ETmax values provided via a separate ET time-series (ETS) file that is independent of the stress-period setup for varying boundary conditions

• Fracture well package (FWL4)
• New flow package (BCF4)
• New recharge/seepage** face package (RSF4)
• New Adaptive Time Stepping and Output Control Package (ATO4)
• New Preconditioned Conjugate Gradient Package containing a new PCG matrix solver (PCG4)
• New Newton Raphson linearization package with backtracking (NRB1)
• Simulate complete desaturation and saturation of grid blocks
• Simulate unsaturated flow
• Includes vapor flow

• Includes fracture well package (FWL4), new flow package (BCF4), recharge/seepage** face package (RSF4)
• Includes new Adaptive Time Stepping and Output Control Package (ATO4)
• Includes new Preconditioned Conjugate Gradient Package containing a new PCG matrix solver (PCG4)
• Includes new Newton Raphson linearization package with backtracking (NRB1)
• Simulate complete desaturation and saturation of grid blocks
• Simulate unsaturated flow includes fractured flow and dual porosity
• Includes solute transport, multiphase transport, NAPL dissolution and volatilization
• Includes vapor flow
• Accurate delineation and tracking of water table position, taking into account flow in the unsaturated zone, delayed yield, and vertical flow components
• Automatic and correct redistribution of the total flow rate of a well screened through multiple model layers when the upper cell(s) are pumped dry
• Accommodation of wellbore storage and overpumped wells
• Prevents water table buildup beyond a specified recharge-ponding elevation
• Handling of seepage face boundary conditions
• Adaptive time-stepping schemes automatically adjusts time-step size to the non-linearities of the system to optimize the solution stability
• Robust and efficient Pre-conditioned Conjugate Gradient matrix solver