PHAST

Criterion

Explanation

General Description

PHAST simulates multi-component, reactive solute transport in three-dimensional saturated groundwater flow systems.

Model Domain

Subsurface saturated zone

Developer

US Geological Survey

Hardware computing requirements

Can be run on most computer systems, including computers with Windows, Linus and Unix OS.
PHAST may require large amounts of memory for execution (primarily dependent upon the number of nodes defined for the simulation grid). Run times may be long on single-processor machines. This is greatly reduced with the parallel (multiprocessor) version of PHAST, which requires libraries for MPI.

Code language

Written in FORTRAN-90, C, and C++

Original applications

PHAST is a versatile groundwater flow and transport simulator that models a wide range of equilibrium and kinetic geochemical reactions. Applicable from laboratory-scale experiments to regional field scales.
Used for studies in:

• Migration of nutrients, inorganic, and organic contaminants, and radionuclides;
  
• Aquifer storage and recovery or engineered remediation;
  
• Natural rock-water interactions in aquifers.
  Not used for unsaturated-zone flow, multiphase flow, or density-dependent flow.

Public/proprietary and cost

Public, No cost

Physically or empirically based

Physically based

Mathematical methods used

Flow and transport calculations are restricted to constant fluid density and constant temperature, based on a modified version of HST3D.
Combined flow, transport, and geochemical processes are simulated by three sequential calculations for each time step.

1. flow velocities calculated
   
2. chemical components transported
   
3. geochemical reactions calculated
   
   The definition of leaky and flux boundary conditions select only exterior cell faces with a specified volume of the model domain, and boundary conditions are restricted to the area of definition, which may include fractions of cell faces.
   Data can be defined in a combination of map and grid coordinate systems, independent of a specific model grid.
   Two-dimensional interpolation is used to define top and bottom surfaces for 3D regions. An area-weighted scheme (natural neighbor interpolation) assigns elevation to a target point based on elevations at the nearest of scattered X, Y points.
   Three-dimensional interpolation assigns porous-media properties, boundary condition properties, or initial conditions of the closest scattered point to a target point. The interpolation allows for groundwater-level elevation and chemical data to be saved at the end of one run and used as initial conditions for a subsequent run, even if the grid spacing has been changed.

Input data requirements

Node-by-node input is not required. Shape data can be imported from ArcInfo shapefiles and ASCII raster files, and from a simple X,Y,Z file format.
Three required input files:

1. flow and transport date file
   
2. chemistry data file
   
3. thermodynamic database file

Outputs

Data may be saved for:

1. Viewing with a text editor
   
2. Exporting to spreadsheets and post-processing programs
   
3. In hierarchical data format (HDF) – a compressed binary format. This HDF file be visualized on Windows Computers using Model Viewer and extracted with the PHASTHDF utility (both distributed with PHAST).

Pre-processing and post-processing tools

USGS Model Muse and Model Viewer

Representation of uncertainty

The model does not have built-in uncertainty representation. This can be assessed for each specific case using sensitivity analysis.

Prevalence

Mostly used in peer-reviewed work

Ease of use for public entities

There are not barriers to public use.

Ease of obtaining information and availability of technical support

A discussion forum and a mailing archive for questions and answers are accessible via https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phast/
Example problems are included in the examples directory of the installation.
Bug reports and other comments can be submitted to h2osoft@usgs.gov.

Source code availability

The source code is available in the /src direc tory of the application.

Status of model development

Fully developed and ready for use

Challenges for integration

Long run times when utilizing geochemical calculations make would make it difficult to couple with surface water models. It has never been used in the Delta.