                                                           File: ABSTRACT.TXT


                    PATRIOT Model System Abstract

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

                             706/546-3549



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                               Summaries

Pesticide Root Zone Model
~~~~~~~~~~~~~~~~~~~~~~~~~
The Pesticide Root Zone Model - 2 (PRZM2) links two subordinate models, PRZM
and the Vadose Zone Flow and Transport Model (VADOFT) to provide a
deterministic simulation of the fate of agricultural pesticides both in the
crop root zone and the underlying unsaturated zone.  The model is capable of
simulating multiple pesticides or pesticide parent and daughter product
relationships, and of estimating probabilities of concentrations or fluxes in
or from various media for the purpose of performing exposure assessments.
The PRZM and VADOFT codes are linked together in PRZM2 with the aid of a
flexible execution supervisor that allows the user to build loading modules
that are tailored to site-specific situations.  In order to perform
probability-based assessments, the code is equipped with a Monte Carlo pre-
and post-processor.

PRZM is a one-dimensional, dynamic, compartmental model that can be used to
simulate pesticide movement in unsaturated soil systems within and
immediately below the plant root zone (1,2).  PRZM has two major components:
hydrology and solute transport.  The hydrologic component for calculating
runoff and erosion is based on the Soil Conservation Service curve number
technique and the Universal Soil Loss Equation.  Evapotranspiration is
estimated either directly from pan evaporation data, or based on an empirical
formula.  Evaporation is divided among evapotranspiration from crop
interception, evaporation from soil, and transpiration by the crop.  Water
movement is simulated by the use of generalized soil parameters, including
field capacity, wilting point, and saturation water content.  The solute
transport component can simulate pesticide application on the soil or on the
plant foliage.  With a newly added feature, biodegradation can also be
simulated in the root zone.  Dissolved, sorbed, and vapor-phase
concentrations in the soil are estimated by simultaneously considering the
processes of pesticide uptake by plants, surface runoff, erosion, decay,
volatilization, foliar washoff, advection, dispersion, and retardation.

PRZM allows simulations of pulse loads, the prediction of peak events, and
the estimation of time-varying mass emission or concentration profiles.
Predictions can be made daily, monthly, or annually. Simulations may extend
to the water table using generally available input data that are reasonable
in spatial and temporal requirements.  PRZM has a separate interactive
processing module to develop and update parameter files for calibration,
verification, and production runs.  Two options are available to solve the
PRZM transport equations:  1) the original backwards-difference implicit
scheme that may be affected by excessive numerical dispersion at high Peclet
numbers, or 2) the method of characteristics algorithm that eliminates
numerical dispersion while slightly increasing model execution time.

VADOFT is a finite-element code that simulates one-dimensional, single-phase
moisture and solute transport in unconfined, variably saturated porous media.
Transport processes include hydrodynamic dispersion, advection, linear
equilibrium sorption, and first-order decay.  VADOFT employs the Galerkin
finite-element technique to approximate the governing equations for flow and
transport and allows for a wide range of nonlinear flow conditions.  Boundary
conditions of the variably saturated flow problems may be specified in terms
of prescribed pressure head or prescribed volumetric water flux per unit
area.  Boundary conditions of the solute transport problem may be specified
in terms of prescribed concentrations of prescribed solute mass flux per unit
area.  All boundary conditions may be time dependent.  An important feature
of the algorithm is the use of constitutive relationships for soil water
characteristic curves based on soil texture.

                          Data Requirements

Daily rainfall and pan evaporation data are required to drive the PRZM
hydrology simulation.  Generalized soil terms including field capacity,
wilting point and saturation must be specified.  The chemical transport
component of PRZM requires information on pesticide volatility, partitioning
and degradation rates.  Constitutive relationships between pressure, water
content, and hydraulic conductivity may be used to solve the VADOFT flow
equations.  The users manual provides detailed guidance on parameter
estimation and model operation as well as an example application (3).

                                Output

The output of a PRZM2 assessment is a time series of pesticide leachate mass
and concentration leaving the root zone and entering the water table.  This
represents a measure of the potential for leaching of the pesticide given
daily changes in precipitation, evapotranspiration, cropping practices, land
management activities, and application timing.

                     Assumptions and Limitations

PRZM2 is limited to estimation of the vertical movement of contaminants.
Hydrologic and hydraulic computations are performed on a daily time step even
though finer time steps may be used for some of the processes to ensure
greater accuracy in the simulation.  Hysteresis effects in the constitutive
relationships are assumed to be negligible.  Sorption and decay of the solute
are described by a linear equilibrium isotherm and a lumped first-order decay
constant.  The code considers only single porosity soil media and does not
simulate flow or transport in fractured porous media or structured soils.

                         Application History

The PRZM model has been used in a wide range of regulatory applications for
the USEPA.  Specific applications can be reviewed in the references (1,4,5).
A screening methodology based on prepared scenarios using PRZM has been used
to evaluate pesticide leaching potential (6).  PRZM has been validated with
both field data and model experiments and has been reviewed by independent
experts.  Three sets of benchmark problems were used to test the VADOFT code;
numerical results from VADOFT were compared with analytical solutions and
results using two other finite-element codes (3).

                             Enhancements

For all changes/enhancements, refer to the "Model Enhancements and
Description of Bridge Programs for PRZM-2/HSPF and PRZM2/WASP Applications
--Addendum to the Users Manual for Release 2.0 of the PRZM-2 Model"
documentation file in WordPerfect (binary) format.  For further information,
refer to file PRZDOCAD.DOC.

Donigian, A.S., Jr., R.F. Carsel, J.C. Imhoff, and P.R. Hummel.  1994.  Model
Enhancements and Description of Bridge Programs for PRZM-2/HSPF and
PRZM2/WASP Applications--Addendum to the Users Manual for Release 2.0 of the
PRZM-2 Model.  U.S. Environmental Protection Agency, Athens GA.
(In Preparation).


Pesticide Assessment Tool for Rating Investigations of Transport
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Pesticide Assessment Tool for Rating Investigations of Transport
(PATRIOT) is designed to provide rapid analyses of ground water vulnerability
to pesticides on a regional, state, or local level.  PATRIOT assesses ground
water vulnerability by quantifying pesticide leaching potential in terms of
the pesticide mass transported to the water table.  This software package
integrates, in a PC environment, a tool that enables analysis of pesticide
leaching potential with the data required for area-specific analysis anywhere
in the conterminous U.S.  PATRIOT is composed of 1) a pesticide fate and
transport model (PRZM2, see above), 2) a comprehensive database, 3) an
interface that facilitates database exploration, 4) a directed sequence of
interaction that guides the user in providing all the necessary information
to perform alternative model analyses, and 5) user-selected methods of
summarizing and visualizing model results (7).

The users of PATRIOT are expected to be State personnel charged with
developing pesticide management plans as well as other regulatory and
resource management institutions.  PATRIOT is designed specifically for
minimal user input and rapid analyses in a PC environment; interaction with
both the model and the databases has been implemented using the interface
development tool ANNIE-IDE (8).  ANNIE-IDE is used in PATRIOT to facilitate
on-line documentation and assistance, analyses of databases, development of
model input and execution, and selection of evaluation options for model
output.

                          Data Requirements

Ground water vulnerability assessments for a specific geographic area
requires data on the influx of water and pesticide, soils properties and
distribution, pesticide chemodynamics, agricultural practices, and the
distance from the soil surface to ground water.  PATRIOT includes databases
that satisfy rainfall (10 years of daily rainfall from primary NOAA weather
stations), soils properties and occurrence (NRI/SOILS5 linked database (9)),
pesticide properties (SCS/ARS/CES Pesticide Properties Database (10)), and
cropping practices (EPA cropping practices database (11)).  Pesticide-crop
relationships and depth to water table estimates must be supplied by the
user.

                                Output

PATRIOT outputs graphic comparisons of the leaching potential for various
combinations of pesticide, soil, rainfall, and agricultural practices.
Output options allow reporting of either unit or area-weighted leaching
analyses aggregated within geographic boundaries.  For a selected period of
analyses, either average annual or total leaching can be reported.  In
addition, PATRIOT enables the viewing of many intermediate tables, maps, and
graphics that support the user and help them to understand the impact of
decisions in site characterization.  A supplemental feature of the model is
the ability to perform Monte Carlo simulations for evaluating the effect of
uncertainty in pesticide and soil properties on pesticide transport.

                     Assumptions and Limitations

See PRZM2 above.

                         Application History

See PRZM2 above.

                              References

1.  Carsel, R. F., C. N. Smith, L. A. Mulkey, J. D. Dean, and P. Jowise.
1984.   User's Manual for the Pesticide Root Zone Model (PRZM).
EPA/600/3-84-109, U.S. EPA, Athens, GA, 30605.

2.  Carsel, R. F., L. A. Mulkey, M. N. Lorber, and L. B. Baskin.  1985.  The
Pesticide Root Zone Model (PRZM): A Procedure for Evaluating Pesticide
Leaching Threats to Ground Water.  Ecol. Modeling, 30:49-69.

3.  Mullins, J.A., R.F. Carsel, J.E. Scarbrough, and A.M. Ivery.  1993.
PRZM-2, A Model for Predicting Pesticide Fate in the Crop Root and
Unsaturated Zones:  Users Manual for Release 2.0.  EPA/600/R-93/046, U.S.
EPA, Athens, GA, 30605.

4.  Carsel, R. F., W. B. Nixon, and L. B. Ballantine.  1986.  Comparison of
Pesticide Root Zone Model Predictions with Observed Concentrations for the
Tobacco Pesticide Metalaxyl in Unsaturated Zone Soils.  Environ. Toxicol.
Chem., 5:345-353.

5.  Melancon, S. M., J. E. Pollard, and S. C. Hern.  1986.  Evaluation of
Sesoil, PRZM and PESTAN in a Laboratory Column Leaching Experiment.  Environ.
Toxicol. Chem., 5:865-878.

6.  Dean, J. D., P. P. Jowise, and A. S. Donigian.  1984.  Leaching
Evaluation of Agricultural Chemicals (LEACH) Handbook.  EPA/600/3-84/068,
U.S. EPA, Athens, GA, 30605.

7.  Imhoff, J.C., P.R. Hummel, J.L. Kittle, Jr., and R.F. Carsel.  1993.
PATRIOT - A Methodology and Decision Support System for Evaluating the
Leaching Potential of Pesticides.  U.S. EPA, Athens, GA, 30605.

8.  Kittle, J.L. Jr., P.R. Hummel, and J.C. Imhoff.  1989.  ANNIE-IDE, A
System for Developing Interactive User Interfaces for Environmental models
(Programmers guide). EPA/600/3-89/034, U.S. EPA, Athens, GA, 30605.

9.  Goebel, J.J.  1991.  "Description of the National Resources Inventory."
Appendix D of Agrichemical Chemical Use and the Potential for Groundwater
Contamination:  How Big is the Problem?  Draft Report.  National Center
for Resource Innovations and the Economic Research Service, Soil Conservation
Service, and the Cooperative State Research Service of the U.S. Dept. of
Agriculture, Washington, DC.

10. Wauchope, R.D., A.G. Hornsby, D.W. Goss, and J.P. Burt.  1990.  The
SCS/ARS/CES Pesticide Properties Database: I, A Set of Parameter Values for
First-Tier Comparative Water Pollution Risk Analysis.  In:  Pesticides in the
Next Decade:  The Challenges Ahead.  Virginia Water Resources Research
Center, Blacksburg, VA.

11. Bird, S.L., M.J. Cheplick, R.F. Carsel, and M.J. Fendley.  1991.  User's
Guide for the PRZM Input Collator (PIC Version 1.0).  U.S. Environmental
Protection Agency, Athens, GA. (Unpublished Report).
