                                                           File: ABSTRACT.TXT


                        PRZM Model System Abstract


               Center for Exposure Assessment Modeling (CEAM)
     National Exposure Research Laboratory - Ecosystems Research Division
                  Office of Research and Development (ORD)
               U.S. Environmental Protection Agency (U.S. EPA)
                          960 College Station Road
                         Athens, Georgia 30605-2700

                                706/355-8400



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                                  Summary

This publication contains documentation for the PRZM-3 model.  PRZM-3 is the
most recent version of a modeling system that links two subordinate models--
PRZM and VADOFT--in order to predict pesticide transport and transformation
down through the crop root and unsaturated zone.  Enhancements to Release
3.0 include algorithms that enable modeling of nitrogen cycle soil kinetic
processes with the ability to track nitrogen discharges from a septic tank
into the soil environment and movement to groundwater.  Additional
enhancements enable better simulation of physicochemical processes, increased
flexibility in representing agronomic practices, and improved post-processing
and data interpretation aids.  

PRZM is a one-dimensional, finite-difference model that accounts for
pesticide and nitrogen fate in the crop root zone.  PRZM-3 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 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 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.  In order to perform probability-based exposure assessments, the
code is also equipped with a Monte Carlo pre- and post-processor.

                                 Disclaimer

The information in the PRZM3 User's Manual has been funded wholly or in part
by the United States Environmental Protection Agency under Contract
No. 68-C6-0020 to HydroGeoLogic, Inc.  It has not been subject to the
Agency's peer and administrative review, and therefore it has not been
approved for publication as an EPA document.  Certain of the model code
enhancements have received preliminary evaluation by either AQUA TERRA
Consultants, Waterborne Environmental, Inc. or the U.S. Environmental
Protection Agency.  Additional peer and administration review and testing is
ongoing, but not yet completed.  In no event shall AQUA TERRA Consultants or
Waterborne Environmental, Inc. be liable for any loss of profit or any
commercial damage, including but not limited to special, consequential, or
other damages resulting from the use of this software.  Mention of trade
names of commercial products does not constitute endorsement or
recommendation for use by the U.S. Environmental Protection Agency.

                                Documentation

The PRZM3 User's Manual is available as WordPerfect (version 6.1) documents
in (binary, non-ASCII) files INTRO.WPD, CHAP1.WPD, CHAP2.WPD, CHAP3.WPD,
CHPT4.WPD, CHAP5.WPD, CHPT6.WPD, CHAP7.WPD, CHAP8.WPD, CHAP9.WPD, CHAP10.WPD,
and CHAP11.WPD within the DOCUMENT sub-directory.  Refer to file READ.ME in
the README sub-directory for further information on the storage format and
hardware and/or software print/view requirement(s) of the user's manual
files.

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