logo U.S. Environmental Protection Agency Argonne National Laboratory U.S. Army Corps of Engineers

Glossary

A B C D E F G H I L M N O P Q R S T U V W Z

Uncertainty
The term uncertainty refers to the inherent unknown quantities present in all scientific and technical decisions. Uncertainties can arise from incomplete knowledge of the nature and extent of contamination, an inability to predict a technology's performance under site-specific conditions, or new or changing regulatory requirements.

Underground Injection Control (UIC)
UIC is the prevention of contamination from fluids disposed through underground injection. Regulated under the Safe Drinking Act, the UIC program was established to prevent contamination of underground sources of drinking water. In addition to banning certain types of injection, the program establishes minimum requirements for the siting of injection wells and the construction, operation, maintenance, monitoring, testing, and closure of wells.

Underground Storage Tank (UST)
An UST is a tank and any underground piping connected to a tank that is used to contain gasoline or other petroleum products or chemical solutions and that is placed in such a manner that at least 10 percent of its combined volume is underground.

Unexploded Ordnance (UXO)
The term exploded ordnance refers to any munition, weapon delivery system, or ordnance item that contains explosives, propellants, and chemical agents. UXO consists of the same items after they: (1) have been armed or otherwise prepared for action; (2) have been launched, placed, fired, or released in such a manner as to constitute a hazard to operations, installations, personnel, or material; and (3) remain unexploded by design, by malfunction, or for any other reason.

Unsaturated Zone
The unsaturated zone is the area between the land surface and the uppermost aquifer (or saturated zone). The soils in an unsaturated zone may contain air and water.

USTFields Initiative
The USTFields Initiative undertaken by EPA's Office of Underground Storage Tanks (OUST) focuses on improving cleanups at sites affected by petroleum contamination and encouraging redevelopment of these sites.



Acronyms Glossary Contact Us
Disclaimer, Privacy, and Security Notice | Notice of Use
You will need the free Adobe Reader to view some of the files on this site.
Download the Adobe® Reader® | See EPA's PDF page to learn more.