Underground storage tank

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An Underground storage tank (UST) is, according to United States federal regulations, a storage tank, not including any underground piping connected to the tank, that has at least 10 percent of its volume underground.

A horizontal cylindrical steel tank with a factory applied coating and galvanic anodes prior to installation underground.

Definition in U.S. federal law[edit]

"Underground storage tank" or "UST" means any one or combination of tanks including connected underground pipes that is used to contain regulated substances, and the volume of which including the volume of underground pipes is 10 percent or more beneath the surface of the ground.[1] 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 for storing heating oil for consumption on the premises, or septic tanks.

In September 1988, the U.S. Environmental Protection Agency (EPA) published 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.[2]

Tank types[edit]

Underground storage tanks fall into four different types:

  1. Steel/aluminum tank, made by manufacturers in most states and conforming to standards set by the Steel Tank Institute.
  2. 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.
  3. Tanks made from composite material, fiberglass/aramid or carbon fiber with a metal liner (aluminum or steel). See metal matrix composite.
  4. Composite tanks such as carbon fiber with a polymer liner (thermoplastic). See rotational molding and fibre-reinforced plastic (FRP).

Petroleum underground storage tanks[edit]

Petroleum USTs are used throughout North America at automobile filling stations and by the US military. Many have leaked, allowing petroleum to contaminate the soil and groundwater and enter as vapor into buildings, ending up as brownfields or Superfund sites.[citation needed] Many USTs installed before 1980 consisted of bare steel pipes, which corrode over time. Faulty installation and inadequate handling may also cause leaks.[citation needed]

Regulation in the US[edit]

USTs are regulated in the United States to prevent release of petroleum and contamination of groundwater, soil and air. The 1984 Hazardous and Solid Waste Amendments to the Resource Conservation and Recovery Act (RCRA) required EPA to develop regulations for the underground storage of motor fuels to minimize and prevent environmental damage, by mandating owners and operators of UST systems to verify, maintain, and clean up sites damaged by petroleum contamination.[3]

In December 1988, EPA regulations asking owners to locate, remove, upgrade, or replace underground storage tanks became effective. Each state was given authority to establish such a program within its own jurisdiction, to compensate owners for the cleanup of underground petroleum leaks, to set standards and licensing for installers, and to register and inspect underground tanks.[citation needed]

Most upgrades to USTs consisted[when?] 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.[citation needed]

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.[citation needed]

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.[citation needed]

U.S. regulations required 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.[4]

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.[citation needed]

The EPA Underground Storage Tank Program is considered to have been very successful.[according to whom?] 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.[citation needed] Of the approximately one million underground storage tanks sites in the United States as of 2008, most of which handled some type of fuel, an estimated 500,000 have had leaks.[5] As of 2009, there were approximately 600,000 active USTs at 223,000 sites subject to federal regulation.[6] In 2012, EPA published how to screen buildings vulnerable to petroleum vapor intrusion,[7] and in June 2015, U.S. EPA finally released its "Technical Guide for Assessing and Mitigating the Vapor Intrusion Pathway from Subsurface Vapor Sources to Indoor Air" and "Technical Guide For Addressing Petroleum Vapor Intrusion At Leaking Underground Storage Tank Sites"[8]

See also[edit]


  1. ^ U.S. Environmental Protection Agency (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.
  2. ^ EPA (1988). "Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST)." Federal Register, 53 FR 37194, 1988-09-23. 40 CFR Part 280.
  3. ^ United States. Hazardous and Solid Wastes Amendments of 1984, P.L. 98-616, 98 Stat. 3224, November 8, 1984.
  4. ^ 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.
  5. ^ Eileen Sullivan, "Cold War era fuel tanks could be leaking hazardous material into environment", Associated Press, August 12, 2008
  6. ^ EPA (2010). "FY 2009 Annual Report On The Underground Storage Tank Program." Document no. EPA-510-R-10-001.
  7. ^ John T. Wilson, James W. Weaver, Hal White (December 2012). "An Approach for Developing Site-Specific Lateral and Vertical Inclusion Zones within which Structures Should be Evaluated for Petroleum Vapor Intrusion due to Releases of Motor Fuel from Underground Storage Tanks (EPA 600/R-13/047)" (pdf). US EPA. p. 34. Retrieved 13 June 2015. 
  8. ^ "EPA Technical Documents, Tools and Other Resources to Support Vapor Intrusion Assessment and Mitigation Activities". US EPA. 12 June 2015. Retrieved 13 June 2015. 

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