Developing a flexible system for multipathway environmental risk analysis.

Background and Introduction Most existing computer codes for environmental pathway modeling were developed to satisfy a specific objective (e.g., perform analyses to demonstrate regulatory compliance). Over time, the codes have been enhanced to assess the impacts to receptors from exposure to multiple pathways (e.g., air, water, and soil). Such capabilities require the ability to model material transfer between different media in addition to the ability to model physical and chemical reactions, dispersion, transport, and uptake. Such previous enhancements were often added without regard to the overall structure of the code, making future expansion difficult. Furthermore, these codes have been written in various computer languages and software environments that are often not compatible with each other. In recent years, largely driven by advances in industrial software development, a new concept for software development based on “modularization” has emerged. This approach entails the development of common “modules” or components that can be shared by and used in different applications that have certain common needs. For instance, an air dispersion model can be written into a common component to be shared by several different applications, each with the need to model air dispersion of some release. When fully developed, the modeling application would become an exercise of selecting, integrating, and applying a consistent combination of appropriate modules for a