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Model Report


Last Revision Date: 08/25/2009 View as PDF
General Information Back to Top
Model Abbreviated Name:

Model Extended Name:

Model Overview/Abstract:
PRZM3 is a modeling system that links two subordinate models - PRZM and VADOFT to predict pesticide transport and transformation down through the crop root and unsaturated zone. PRZM3 includes modeling capabilities for such phenomena as soil temperature simulation, volatilization and vapor phase transport in soils, irrigation simulation, microbial transformation, and a method of characteristics (MOC) algorithm to eliminate numerical dispersion.

PRZM is a one-dimensional, finite-difference model that accounts for pesticide and nitogen fate in the crop root zone. PRZM is capable of simulating transport and transformation of the parent compound and as many as two daughter species.

VADOFT is a one-dimensional finite-element code that solves the Richard's equation for flow in the unsaturated zone. The user may make use of constitutive relationships between pressure, water content, and hydraulic conductivity to solve the flow equations. Vadoft may also simulate the fate of two parent and two daughter products.

The PRZM and VADOFT codes within PRZM3 are linked together with the aid of a flexible execution supervisor that allows the user to build loading models that are tailored to site-specific situations. To perform probability based exposure assessments, the code is also equipped with a Monte Carlo pre- and post-processor.

Model Technical Contact Information:
Dirk F. Young, Ph.D.
Environmental Fate and Effects Division (mail code: 7507P)
Office of Pesticides, USEPA
1200 Pennsylvania Ave, NW
Washington, DC 20460-0001
ph: (703) 605-0206
fax: (703) 305-6309
Model Homepage: http://www.epa.gov/ceampubl/gwater/przm3/index.htm

User Information Back to Top
Technical Requirements
Computer Hardware
Pentium with 16 MB RAM and 100 MB ROM (minimum)
Other Software Required to Run the Model
Download Information
The model is publicly available from the U.S. EPA.


Using the Model
Basic Model Inputs
Complex model with substantial input requirements, including some site-specific inputs.
User Support
User's Guide Available?


There are some parameters that require calibration.

Documentation can be downloaded from:



Provides: (1) an abstract or abstract equivalent in the introduction, (2) schematic/diagram showing model structure and interaction of model components, (3) equations, equation solution methodologies, and related simplifying assumptions, (4) example input/output files, (5) input and output variable documentation including definitions, units, temporal/spatial dimensions, temporal/spatial resolution options, and (if applicable such as with FORTRAN) format, (6) guidance on selecting and/or estimating values and/or distributions for input variables (including guidance on calibration and selecting default values and/or distributions), (7) guidance on the analysis and interpretation of output, and (8) description of sensitivity analysis, uncertainty analysis, and testing (validation) methodologies and results.

User Qualifications
User needs high level of technical education and/or modeling experience.

Model Science Back to Top
Summary of Model Structure and Methods
Simulates formation and fate/transport of daughter products of primary pollutants.

The model provides mathematical guidance to assist the user when selecting modeling parameters.

The model uses a modeling framework that links several related models, modules, or sub-models.

Governing equations are solved numerically with Monte Carlo simulation

Model Evaluation
Code verification has been performed.


Moderate model testing (evaluation) has been performed by the FIFRA Model Validation Workgroup.


Sensitivity analysis has been performed and is presented in the POPS report.


Model has been externally peer reviewed.

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