http://www.epa.gov/ceampubl/

EPA's Center for Exposure Assessment Modeling provides proven predictive exposure assessment techniques for aquatic, terrestrial, and multimedia pathways for organic chemicals and metals, and distributes Environmental Simulation Models and Databases for urban and rural nonpoints sources, conventional and toxic pollution of streams, lakes and estuaries, tidal hydrodynamics, geochemical equilibrium, and aquatic food chain bioaccumulation.