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 ------- 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). ------- |