Simulates air flow and the advective transport of vapor in unsaturated soils using MODFLOW


Introduction to P3DAIR
P3DAIR Frequently-Asked Questions
P3DAIR Requirements


P3DAIR can be used to simulate the movement of air and the advective transport of vapor in unsaturated soils. P3DAIR is particularly useful for delineating contaminant capture zones and evaluating the effectiveness of vapor extraction wells. P3DAIR is recommended for use with MODAIR which is a MODFLOW-based software package for modeling air flow in the unsaturated zone. P3DAIR uses the input files and pressure solution of MODAIR. However, it can be readily modified to work in conjunction with any other block-centered finite-difference flow model. P3DAIR generates output files containing: x,y,z coordinates at different travel times along the path of each individual particle; x,y,z coordinates of all the particles at a user-specified time; and initial and final positions of particles captured by various sinks or sources in the case of backward tracking. P3DAIR produces output files of pathlines of individual particles, positions of displacement fronts of capture zones at desired time, and distribution of captured particles.


What is P3DAIR?
P3DAIR is a general particle-tracking program for calculating air flow paths and travel time within the unsaturated zone. The program can be used for two- or three-dimensional simulations of either steady-state or transient flow. P3DAIR was developed to facilitate the analyses of soil vapor extraction systems but it can also be used to analyze a broad range of problems regarding air flow in the unsaturated zone. P3DAIR uses the air-pressure solutions from MODAIR, an air flow simulator developed by Guo (1996). MODAIR uses MODFLOW, the USGS three-dimensional finite-difference ground-water flow model (McDonald and Harbaugh, 1988) to calculate air pressure after the appropriate conversions are made to the input data.

How different is P3DAIR from PATH3D?
P3DAIR is based on PATH3D, the general ground-water particle tracking program developed by Zheng (1989). P3DAIR and PATH3D are identical in most respects and those users familiar with PATH3D should be able to use P3DAIR almost immediately. All the utility programs accompanying PATH3D can be applied for air flow particle tracking directly without modification.

How does P3DAIR interface with MODAIR?
P3DAIR relies on a flow model, e.g., MODAIR, to supply the flow solution. P3DAIR reads the flow solutions (i.e., air pressure at each cell) and calculates the distribution of specific velocity. Some input files for MODAIR are directly used by P3DAIR. Users, however, do not have to use MODAIR to generate the flow solution that P3DAIR needs to run. The pressure solutions can be generated in many different ways and used by P3DAIR as long as the formats of pressure solutions are recognized by P3DAIR.

Does P3DAIR support the PCB package?
Yes. The PCB (time-varying constant-pressure boundary) package is implemented in MODAIR and is supported in P3DAIR.

P3DAIR Requirements: PC 486/Pentium with 2 MB RAM. Requires SURFER or other graphics package for output graphics.