United States Environmental Protection Agency	Office of Research and Development

National Exposure Research Laboratory
Research Abstract

Government Performance Results Act (GPRA) Goal #4.5.2
Annual Performance Measure #243

Significant Research Findings:

SPRAYTRAN User's Guide: A GIS-Based Spray Droplet
Dispersion Modeling System

Scientific
Problem and
Policy Issues

Research
Approach

The drift of airborne pesticides beyond the target site during agricultural spray
applications is a source of environmental concern because of the potential for
human health impacts, downwind contamination and damage to crops and
livestock, and endangerment of ecological resources. The amount and ultimate
destination of these airborne pesticides is a function of application techniques,
environmental conditions, and physical properties of the spray solution. The
sensitivity of drift to numerous factors, including atmospheric conditions, terrain
features, and application equipment, makes the use of models necessary for
evaluating the potential risks of spray operations and the potential effectiveness of
mitigation options. The U.S. Environmental Protection Agency (EPA), Office of
Pesticide Programs (OPP), currently uses the AGDISP model to evaluate near-
field pesticide drift (<300 m) from a single pesticide application. OPP lacks the
tools to adequately evaluate mesoscale drift (1-50 km) from applications to
multiple fields.

A number of models have been developed to predict the drift and deposition from
aerial spray applications. Resolution and representation of the effects of
equipment and near-field dynamics in the flow fields in the vicinity of the aircraft
have been addressed using LaGrangian modeling approaches. LaGrangian models
track a cohort of droplets in a given drop size category and overlay a random
component to account for atmospheric turbulence. The LaGrangian approach
lends itself to detailed modeling of the effects of application equipment on spray
dispersal and can be used to evaluate the mitigating effects of alternative
equipment uses and near-field buffer zones.

AGDISP is based on a LaGrangian approach to the solution of the spray material
equations of motion and includes simplified models for the effects of the aircraft
wake and air-generated and ambient turbulence. AGDISP evaluates many
particle-size classes and includes evaporation algorithms for volatile carriers. It is
used by the U.S. Department of Agriculture Forest Service to evaluate and manage
spray applications and forms the bases of a regulatory tool for use by EPA's OPP
to evaluate impacts from pesticide drift in the pesticide registration process. The
model is recommended for use within 300 m of the application area and simulates
a single application to a field-scale area. AGDISP does not incorporate the
impacts of variable terrain or time-varying nonuniform meteorology.

A comprehensive assessment of the impacts of pesticide applications in a
watershed or community requires the ability to evaluate applications to multiple


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Results and
Impact

Research
Collaboration
and Research
Products

Future Research

Contacts for

Additional

Information

fields in an area with variable terrain. The SPRAY TRANsport (SPRAYTRAN)
system described in this document links output from the AGDISP near-field
equipment simulation to the CALMET/CALPUFF atmospheric modeling system
through a geographic information system (GIS) interface developed for the U.S.
Department of Defense (DoD). SPRAYTRAN estimates mesoscale (1-50 km)
pesticide drift and dispersion from agricultural spray operations.

SPRAYTRAN was developed to link the detailed spray application equipment
modeling of AGDISP to the longer range transport of pesticide droplets over
variable terrain and with variable meteorological modeling found in the
CALMET/CALPUFF through a GIS interface. This linked system enables the
estimation of pesticide exposures from multiple spray application areas at a
community or small watershed scale.

SPRAYTRAN was developed in collaboration with the U.S. Forest Service
through a contract with the Pacific Northwest National Laboratory, which is
operated for the Department of Energy by Battelle. SPRAYTRAN expands the
DUSTRAN framework developed for DoD through the Strategic Environmental
Research and Development Program.

Near term research efforts related to further SPRAYTRAN development include
reduction of the CALPUFF averaging time step, refinement of AGDISP two-
dimensional depositional algorithms, incorporation of a version of AGDISP
containing ground spray simulation algorithms, and field testing the
SPRAYTRAN simulation package. Longer term research plans also include
incorporation of secondary drift algorithms into the SPRAYTRAN system and
converting to a GIS platform consistent with other National Exposure Research
Laboratory modeling efforts.

Questions and inquiries can be directed to:

Sandra L. Bird

U.S. EPA, Office of Research and Development
National Exposure Research Laboratory
Ecosystems Research Division
960 College Station Road
Athens, GA 30605-2700
Phone: 706/355-8318
E-mail: bird.sandra@epa.gov
Funding for this project was through the U.S. EPA's Office of Research and
Development, National Exposure Research Laboratory, and the work was
conducted by the (Ecosystems Division).


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