EPA uses a wide variety of scientific and technical models to support our decisions and policies. These models increase the level of understanding about natural systems and the way in which they react to varying conditions, including the spread of toxic substances in various media, the short- and long-term effects of exposure to hazardous substances, and other forms of prediction and risk assessment. They estimate the environmental fate of pollutants, their impacts on human health and the environment, and the costs and benefits of alternative policies. Frequently, these models become the basis for environmental cleanup, protection, or regulation. Models therefore underlie how the Agency chooses to address a multitude of environmental questions.

Models themselves can become part of the controversy over environmental initiatives. Parties affected by EPA regulations have at times challenged these regulations in court by questioning the validity of the models upon which they were based. EPA's 2002 Information Quality Guidelines (PDF) (57 pp, 144 KB, about PDF) established a process for parties affected by the Agency's use of models to question the data, methods, and assumptions underlying these models.

Models Knowledge Base

The best place to search for and learn about the models upon which EPA relies is in the Models Knowledge Base, a central repository developed by EPA's Council for Regulatory Environmental Modeling (CREM).

The Knowledge Base provides for each model:

• technical requirements,
• basic information on how to use it,
• information on the its conceptual basis, scientific detail and model evaluation, and
• directions for downloading it and links to further information.

While the Knowledge Base does not yet include every model EPA uses, it does include the models that EPA's program offices have identified as most frequently used.

Additional Models

Although the Models Knowledge Base includes many of the models commonly used within the EPA, the following links to modeling groups within EPA provide information on additional models that have not yet been included in the Knowledge Base.

Atmospheric Modeling - Simulate the fate and transport of pollution through the atmosphere. This information is used in developing emission control policies and regulations.

Computational Toxicology - Determine the ways chemicals affect our bodies and the resulting health effects.

Economic Enforcement - Analyze financial effects of enforcement decisions, such as whether companies can afford various options.

Exposure Assessment - Determine how chemicals affect the air, water, and land.

Indoor Air Quality Modeling - Analyze how pollutants affect indoor air quality and provide data for exposure and risk assessments.

Pesticides in Water - Predict pesticide concentrations in ground and surface water; results are used in human health and aquatic ecological exposure assessments.

Regulatory Atmospheric Modeling - Evaluate options for controlling air pollution and their effects on various sources.

Subsurface Modeling - Analyze the fate and transport of contaminants below ground; results are used in risk assessment, site characterization and remediation, wellhead protection, and geographic databases.

Vehicle Emissions - Predict emissions from on-road vehicles, nonroad sources, and fuels under varying conditions.

Water Quality - Simulate the precipitation and pollutant movement from ground surface to their release in receiving waters. Learn about these models and tools: AQUATOX, Cornell Mixing Zone Expert System (CORMIX), Water Quality Analysis Simulation Program (WASP), River and Stream Water Quality Model (QUAL2K), DFLOW and BASINS.

Watershed and Water Quality - Help develop Total Maximum Daily Loads (TMDL), waste load allocations, and watershed protection plans. Learn more about these models: Loading Simulation Program in C++ (LSPC), Watershed Assessment Model (WAM), Storm Water Management Model (SWMM) and Watershed Analysis Risk Management Framework (WARMF).