Chemicals, Special Topics in Environmental Management

UST Best Management Practices: Leak Detection

  • You can detect a leak from any portion of the tank or the connected underground piping that routinely contains petroleum
  • Your leak detection is installed, calibrated, operated, and maintained in accordance with the manufacturer’s instructions, including routine maintenance and service checks for operability or running condition; and
  • Your leak detection meets the performance requirements described in the federal regulations 40 CFR 280.43 or 40 CFR 280.44.

Leak detection systems are also required for underground piping connected to the UST. Different systems are used depending on whether the pipes are suction or pressurized. Pressurized pipes must use two types of leak detection systems, such as an automatic line leak detector and an annual line tightness test.

Note: State or local regulations may differ from the federal requirements, so find out which requirements apply to your UST.

Leak Detection Methods

EPA has identified the following methods that owners and operators may use to meet the federal leak detection requirements:

  • Secondary containment with interstitial monitoring
  • Automatic tank gauging systems (including continuous ATG systems)
  • Vapor monitoring (including tracer compound analysis)
  • Groundwater monitoring
  • Statistical inventory reconciliation
  • Other methods meeting performance standards

The leak detection methods noted above are all monthly monitoring methods and eventually everyone must use at least one of them. However, as temporary method, you can combine tank tightness testing with inventory control (or with manual tank gauging if you have a small tank).

Secondary Containment with Interstitial Monitoring
The Energy Policy Act of 2005 requires each new or replaced USTs and piping within 1,000 feet of any existing community water system or potable drinking water well must be secondarily contained and monitored for leaks.

Interstitial monitors are liquid sensors installed in the space between the part of the UST system that holds the fuel and a secondary container that forms a safety barrier to prevent leakage into the environment. Double-walled tanks and excavation liners are examples of secondary containment.  If fuel leaks from the UST into the space between the tank and the secondary barrier, an alarm will be activated.

New dispenser systems within 1,000 feet of an existing community water system or potable drinking water must have under-dispenser spill containment. This requirement does not apply to repairs meant to restore a tank, pipe, or dispenser to operating condition.

Some states have stricter rules requiring secondary containment for all USTs.

Resource: For additional information, see EPA’s guidance document, Grant Guidelines to States for Implementing the Secondary Containment Provision of the Energy Policy Act of 2005.

Automatic tank gauging systems
Automatic tank gauging systems monitor the temperature and level of fuel in a UST, automatically calculating any changes in volume that could indicate a leak.  The system uses a probe permanently installed in the tank and wired to a monitor.

Vapor monitoring
Vapor monitoring measures either product fumes in the soil around the UST or special tracer chemicals added to the UST which escape in order to check for a leak. This method requires installation of monitoring wells that are checked periodically.

Groundwater monitoring
Groundwater monitoring senses the presence of liquid product floating on the groundwater. This method requires installation of groundwater monitoring wells near the tank and along underground piping. This method cannot be used at sites where groundwater is more than 20 feet below the surface.

Statistical inventory reconciliation
Statistical inventory reconciliation uses sophisticated computer software to perform a statistical analysis of inventory, delivery, and dispensing data. Inconsistencies in the data may indicate a leak.

Inventory control
Inventory control measures UST contents, deliveries, and fuel dispensed daily and reconciles these data at least monthly. Inventory control is used in conjunction with a special tank tightness test. Together, these two methods can warn of leaks. This method can be used only temporarily.

Manual tank gauging
Manual tank gauging may be used for tanks of 550 gallons (gal) or less. This leak detection system requires the UST to be taken out of service for at least 36 hours, during which time no liquid is added to or removed from the tank. Level measurements are based on the average of two consecutive stick readings at both the beginning and ending of the period. A leak is suspected if the variation between the beginning and ending measurements meets certain standards outlined in the regulations.

Tanks between 551 and 1,000 gal may use a combination of manual tank gauging and periodic tank tightness for the life of the tank. For tanks with a capacity of 1,001 to 2,000 gal, manual tank gauging must be combined with periodic tightness testing. Tanks greater than 2,000 gal capacity may not use this method of leak detection to meet regulatory requirements.

Resource: For additional information on leak detection methods, see BLR’s article Manual or Computerized Leak Detection.

Petroleum USTs

Owners and operators of petroleum UST systems must provide leak detection for tanks and piping as follows:

  • Tanks must be monitored at least every 30 days for releases using automatic tank gauging, vapor monitoring, groundwater monitoring, interstitial monitoring or other approved method, or monthly inventory control and tank tightness testing every 5 years. This option can be used only for 10 years after installing a new UST or upgrading a UST with corrosion protection. After this 10-year period, monthly monitoring is required.
  • Piping must have devices that automatically shut off or restrict flow or have an alarm that indicates a leak. You must either conduct an annual tightness test of the piping or use one of the monthly leak detection methods. If the UST has suction piping, the leak detection requirements will depend on the type of suction piping. Piping with certain characteristics may not need leak detection:
  • Below-grade piping operating at less than atmospheric pressure is sloped so that the piping’s contents will drain back into the storage tank if the suction is released.
  • Only one check valve is included in each suction line and is located directly below the suction pump.

Suction piping that does not match these characteristics must have leak detection, either monthly monitoring or tightness testing of the piping every 3 years.

Resource: Leak Detection for Underground Piping

Hazardous Substance USTs
Hazardous substance USTs have to meet the same requirements for petroleum USTs concerning correct installation, spill, overfill and corrosion protection, corrective action, and closure. In addition, hazardous substance USTs must have secondary containment and interstitial monitoring for leak detection.

Owners and operators of hazardous substance UST systems must meet the following leak detection requirements:

  • Secondary containment systems must be designed, constructed and installed to:
    • Contain regulated substance released from the tank system until they are detected and removed;
    • Prevent the release of regulated substances to the environment at any time during the operational life of the UST system; and
    • Be checked for evidence of a release at least every 30 days.
  • Double-walled tanks must be designed, constructed, and installed to:
    • Contain a release from any portion of the inner tank within the outer wall; and
    • Detect the failure of the inner wall
  • External liners (included vaults) must be designed, constructed, and installed to:
    • Contain 100 percent of the capacity of the largest tank within its boundary;
    • Prevent the interference of precipitation or groundwater intrusion with the ability to contain or detect a release of regulated substances; and
    • Surround the tank completely (i.e., it is capable of preventing lateral as well as vertical migration of regulated substances).
  • Underground piping must be equipped with secondary containment and be equipped with an automatic line leak detector for underground piping that conveys regulated substances under pressure.

Owners and operators must obtain approval from the regulatory agency to use any alternate release detection method before installation and operation of any new UST system.

Currently EPA requires secondary containment and interstitial monitoring for hazardous substance tanks only.

However, EPA has proposed regulations requiring secondary containment and interstitial monitoring for all new and replaced tanks and piping. The secondary containment must be able to contain regulated substances released from the UST system until they are detected and removed.

Best Management Practices

Check release detection for tanks
Check that each tank at your facility has at least one approved method of release detection.

Check release detection for pressurized piping
Check that each tank’s piping has at least an automatic flow restrictor, automatic shutoff device or continuous alarm in addition to an annual line tightness test or monthly monitoring.

Check detection for suction piping
Check each tank’s piping for at lease one of the following: line tightness testing every 3 years or monthly monitoring. No release detection is required only if it can be verified that you have a safe suction piping system with all of the following characteristics:

X Only one check valve per line located directly below the dispenser

X Piping sloping back to the tank

X System must operate under atmospheric pressure

Resource: This environmental UST checklist Basic Checklist for USTs can be used to audit petroleum and chemical leak detection methods at your facility.

Resource: For additional information on leak detection methods, see EPA’s guidance document Straight Talk on Tanks: Leak Detection Methods for Petroleum USTs and Piping

This is part of a series of UST Best Management Practices (BMPs) designed to help owners and operators comply with UST regulations. Other BMPs include UST overfill protection, and spill buckets.


Nancy W. Teolis, J.D., has been a Legal Editor for BLR’s environmental law publications since 1993, focusing primarily on underground storage tanks, pesticides, and hazardous waste-related requirements. Before joining BLR, she worked for the law firm Rudman & Winchell in Bangor, Maine, with an emphasis on asbestos exposure litigation.  She received her law degree from Western New England University School of Law in Springfield, Massachusetts, and is a member of the Connecticut bar.