Source Term Model Implementation in a Multimedia Modeling System

The integration of source models with transport models can greatly facilitate the process of conducting assessments of impacts from environmental releases. To provide the capability of assessing the potential local and regional impacts from helicopter-based application of pesticides in the SPRAYTRAN (Allwine et. al.2005) linked a spray emission/drift model (AgDISP), with an air dispersion model (CALPUFF)within a GIS system. This linked model system allows investigators to assess release scenarios with automatic transfer of the AgDISP drift rates to the CALPUFF model.

This paper describes the recent implementation of this airborne pesticide application source term model, AgDISP, into a multimedia modeling system, Multimedia Environmental Pollution Assessment System (MEPAS). MEPAS was developed for conducting comprehensive environmental air, water, and soil pathway assessments. MEPAS has linked versions of atmospheric source, dispersion, and risk models. MEPAS also includes a comprehensive constituent database for hazardous chemicals, trace metals, and radionuclides.

The model AgDISP is added to MEPAS to provide the capability of assessing the potential local and regional impacts from helicopter-based application of pesticides. The AgDISP is implemented in a version of MEPAS contained within the model integration modeling platform, FRAMES V2. The FRAMES modeling platform includes software tools to facilitate the implementation of the required input, model-to-model, and output data transfers.

The process of implementation of an unmodifed version of AgDISP model in FRAMES V2 is described. Software tools are described that expedite the formal implementation of such legacy atmospheric dispersion models with minimal, or no, changes in the original software coding. A generic linkage methodology is based on dictionaries are used to define the contents of databases to be transferred information between models (Whelan et. al 1994). A dictionary, or set of dictionaries, defines the parameters needed for model linkage operation. The set of specifications for each parameter to be transferred are defined in these dictionaries – including parameter attributes such as name, dimension, units, type, limits, relationship to other parameters, etc.

The capability created by the inclusion of AgDISP in MEPAS allows the AgDISP model to be easily used in broader applications such as evaluation of potential regional impacts. An example of a source-to-impact analysis using the implemented AgDISP model is presented.