The U.S. Environmental Protection Agency (EPA) in 1980 established the Underground Injection Control (UIC) Program, as mandated by the Safe Drinking Water Act. Under the program, EPA works with state and local governments to regulate waste that is injected into wells in order to prevent contamination of drinking water. A well is defined as a "bored, drilled or driven shaft, or a dug hole, whose depth is greater than the largest surface dimension." (Code of Federal Regulations 40 CFR 144.3)

Injection wells are divided into five classes based on the type of waste injected and where it is injected.

Class I wells inject hazardous and non-hazardous wastes into deep, isolated rock formations that are separated from drinking water sources by many layers of impermeable clay and rock.

Class II wells inject fluids, primarily brine, associated with oil and gas production. Every barrel of oil produced also produces about 10 barrels of brine and that brine must be disposed of.

Class III wells inject super-hot steam, water or other fluid into mineral formations in order to extract minerals such as salt and uranium.

Class IV wells inject hazardous and radioactive wastes into or above underground sources of drinking water. These wells are banned under the UIC program because they directly threaten drinking water.

Class V wells include any injection well not included in the other classes. They are generally shallow holes in the ground that depend on gravity to drain or "inject" liquid waste into the ground. They can range in complexity from shallow storm water drainage wells to large capacity septic systems and sophisticated geothermal reinjection wells. They can pose a threat to drinking water sources if the waste going into them is not controlled.

EPA is studying Class V wells to determine if additional regulations are necessary to protect underground sources of drinking water. EPA expects to publish a final report in September 1999. In addition to other methods of data gathering, EPA is requesting information from the scientific community, academia, environmental organizations, and the public via the Internet. You can find out more information at EPA's Web site (http://www.epa.gov/OGWDW/uic.html).