Underground storage tank
Tank types 
Underground storage tanks generally fall into four different types:
- Steel/aluminum tank, made by manufacturers in most states and conforming to standards set by the Steel Tank Institute.
- Composite overwrapped, a metal tank (aluminum/steel) with filament windings like glass fiber/aramid or carbon fiber or a plastic compound around the metal cylinder for corrosion protection and to form an interstitial space.
- Tanks made from composite material, fiberglass/aramid or carbon fiber with a metal liner (aluminum or steel). See metal matrix composite.
- Composite tanks such as carbon fiber with a polymer liner (thermoplastic). See rotational molding and fibre-reinforced plastic (FRP).
Petroleum underground storage tanks 
USTs, used to store petroleum, are regulated in the United States to prevent release of petroleum and contamination of groundwater. They are used throughout North America at automobile filling stations, and many have leaked, allowing petroleum to contaminate the soil and groundwater.
The Hazardous and Solid Waste Amendments to the Resource Conservation and Recovery Act(RCRA)passed by Congress and signed into law by then president Ronald Reagan in 1984 required the U.S. Environmental Protection Agency (EPA) to develop regulations for the underground storage of motor fuels. These amendments required EPA to develop regulations to minimize and prevent environmental damage, by requiring owners and operators of UST systems to verify, maintain, and, if necessary, clean up sites damaged by petroleum contamination.
Legislation requiring owners to locate, remove, upgrade, or replace underground storage tanks became effective December 23, 1988. Each state was given authority to establish a program within its own jurisdiction to set up a program to compensate owners for the cleanup of underground petroleum leaks, to set standards and licensing for installers, and to register and inspect underground tanks.
Most upgrades to USTs consisted of the installation of corrosion control (cathodic protection, interior lining, or a combination of cathodic protection and interior lining), overfill protection (to prevent overfills of the tank during tank filling operations), spill containment (to catch spills when filling), and leak detection for both the tank and piping.
Many USTs were removed without replacement during the 10-year program. Many thousands of old underground tanks were replaced with newer tanks made of corrosion resistant materials (such as fiberglass, steel clad with a thick FRP shell, and well coated steel with galvanic anodes) and others constructed as double walled tanks to form an interstice between two tank walls (a tank within a tank) which allowed for the detection of leaks from the inner or outer tank wall through monitoring of the interstice using vacuum, pressure or a liquid sensor probe. Piping was replaced during the same period with much of the new piping being double-wall construction and made of fiberglass or plastic materials.
Tank monitoring systems capable of detecting small leaks (must be capable of detecting a 0.1 gallons-per-hour with a probability of detection of 95% or greater and a probability of false alarm of 5% or less) were installed and other methods were adopted to alert the tank operator of leaks and potential leaks.
Regulations included a requirement that UST cathodic protection systems be tested by a cathodic protection expert (minimum every three years) and that systems be monitored to ensure continued compliant operation.
Many owners, who previously stored fuel in underground tanks, switched to above-ground tanks to enable closer environmental monitoring of fuel storage and to reduce costs. Many states, however, do not permit above-ground storage of motor fuel for resale to the public.
The United States Environmental Protection Agency (EPA) Underground Storage Tank Program is generally considered to have been very successful. The national inventory of underground tanks has been reduced by more than half, and most of the rest have been replaced or upgraded to much safer standards. But of the approximately one million underground storage tanks sites in the United States as of 2008, most of which handle some type of fuel, an estimated 500,000 have had leaks. As of 2009, there were approximately 600,000 active USTs at 223,000 sites subject to federal regulation.
Defined in federal law 
Underground storage tank or UST means any one or combination of tanks (including underground pipes connected thereto) that is used to contain an accumulation of regulated substances, and the volume of which (including the volume of underground pipes connected thereto) is 10 percent or more beneath the surface of the ground. This does not include, among other things, any farm or residential tank of 1,100 gallons or less capacity used for storing motor fuel for noncommercial purposes, tanks used for storing heating oil for consumptive use on the premises, or septic tanks.
On September 23, 1988, EPA published stringent underground storage tank regulations, including a 10-year phase-in period that required all operators to upgrade their USTs with spill prevention and leak detection equipment.
See also 
US Laws 
- Hazardous and Solid Wastes Amendments of 1984, P.L. 98-616, 98 Stat. 3224, November 8, 1984.
- U.S. Environmental Protection Agency (EPA), Washington, DC. "Operation and maintenance of corrosion protection." Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST). Code of Federal Regulations, 40 C.F.R. 280.31.
- Eileen Sullivan, "Cold War era fuel tanks could be leaking hazardous material into environment", Associated Press, August 12, 2008
- EPA (2010). "FY 2009 Annual Report On The Underground Storage Tank Program." Document no. EPA-510-R-10-001.
- EPA. "Definitions." Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST). Code of Federal Regulations, 40 C.F.R. 280.12.
- EPA (1988). "Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST)." Federal Register, 53 F.R. 37194, 1988-09-23. 40 CFR Part 280.