Graphical Exposure Modeling System (GEMS)

The "Graphical Exposure Modeling System (GEMS)" is a interactive
information management system designed to allow the rapid
analysis of environmental problems. The system allows the user
to estimate chemical properties of pollutants, assess the fate
of chemicals in theoretical and in geographically specific
environments, model the resulting chemical concentrations,
determine the number of people potentially exposed, and estimate
the resultant human exposure and risk. GEMS has modeling
capabilities for the atmosphere, surface water, unsaturated land
(soil), saturated zones (ground water), and multimedia. GEMS
contains a variety of models for each media.

GEMS contains a range of data sets that help the user determine
the environmental characteristics of the specific area. These
include data on the population (including demographic
characteristics as well as location of cities), atmosphere,
water, and soil characteristics (e.g., climatic, soil property,
and stream flow data), ecosystem characteristics, and water
supply information. GEMS also includes data sets that identify
and characterize potential chemical release sites as well as
monitoring stations. These data sets include information on
publicly owned wastewater treatment works (POTWs), and
industrial facilities, identified through the Permit Compliance
System (PCS), the National Emissions Data System (NEDS), and the
National Pollutant Discharge Elimination System (NPDES). In
general, the user provides information on the pollutant
discharged such as the amount, concentration, or source.
However, data are also directly accessible from the Toxic
Release Inventory (TRI). Data sets are also available that
provide information on chemicals and their properties.

See: "http://www.epa.gov/"