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Detecting Releases

How can I tell if a UST is leaking?

There are several warning signs of leaks from USTs or piping. Unusually strong petroleum vapors, dying vegetation near the tank and erratic equipment operation (unexplained presence of water in the tank) are all indicators of a possible release. Tanks that seem to require more fuel than they are using or experience a sudden loss of product may also be leaking.

Why is release detection crucial?

All regulated tanks and piping must have release detection so that leaks are discovered quickly before contamination spreads from the UST site. You must provide your UST system with release detection (often also called leak detection) that allows you to meet three basic requirements:

  1. You can detect a leak from any portion of the tank or its piping that routinely contains petroleum;
  2. Your leak detection is installed, calibrated, operated, and maintained in accordance with the manufacturer's instructions; and
  3. Your leak detection meets the performance requirements described in the federal regulations (sections 280.43 and 280.44).
The leak detection requirements are summarized in the table below:


Leak Detection Requirements
UST System Component Leak Detection Method
2 Choices
  1. Monthly Monitoring*; or
  2. Monthly Inventory Control and Tank Tightness Testing Every 5 Years. 
  3. This option can be used only for 10 years after installing a new UST 
    or upgrading an UST with corrosion protection. After this 10-year period, 
    Monthly Monitoring is required.
Pressurized Piping
Choice of one from each set A & set B:
Set A.
  1. Automatic Shutoff Device -or-
  2. Flow Restrictor -or-
  3. Continuous Alarm System
-AND- Set B.
  1. Annual Line Testing -or-
  2. Monthly Monitoring*  
    (except automatic tank gauging)
Suction Piping
3 Choices
  1. Monthly Monitoring* (except automatic tank gauging); or
  2. Line Testing Every 3 Years; or
  3. No Requirements IF the following characteristics are readily determinable:
    • Below-grade piping is sloped so that its contents will drain back into 
      the storage tank if the suction is released.
    • Each suction line has only one check valve which is located directly 
      below the suction pump.
    • System must operate at less than atmospheric pressure.

*Monthly Monitoring Choices in the table above include:

Special note for tanks 2,000 gallons or less in capacity: Tanks 2,000 gallons and smaller 
may be able to use manual tank gauging to meet leak detection requirements (be sure 
you read the link carefully to make sure you meet all the requirements of this method).

What leak detection methods can you use to detect leaks from tanks?

Owners and operators of petroleum USTs must use at least one of the leak detection 
methods below, or other methods approved by their state agency.
  1. Secondary containment and interstitial monitoring
    This involves placing a barrier between the UST and the environment. The barrier 
    provides secondary containment and can be a vault, liner, or the outer wall of a 
    double-walled structure.  Interstitial monitoring methods range from a simple dip 
    stick to automated vapor or liquid sensors permanently installed in the system. 
    All USTs holding hazardous substances that were installed after December 22, 1988 
    must use this method. 
    More detailed information on secondary containment and interstitial monitoring.


  2. Automatic tank gauging (ATG) systems
    ATGs use monitors permanently installed in the tank. These monitors are linked 
    electronically to a nearby control device to provide information on product level 
    and temperature. The gauging system can automatically calculate the changes in 
    product volume that can indicate a leaking tank. This method does not work on 
    piping. More detailed information on automatic tank gauging systems.


  3. Vapor monitoring
    Vapor monitors sense and measure product vapor in the soil around the tank and 
    piping to determine the presence of a leak. This method requires installation of 
    carefully placed monitoring wells. Vapor monitoring can be performed periodically 
    using manual devices or continuously using permanently installed equipment. 
    More detailed information on vapor monitoring.


  4. Groundwater monitoring
    Groundwater monitoring devices sense the presence of liquid product floating on the 
    groundwater. This method requires installation of monitoring wells at strategic 
    locations in the ground near the tank and along the piping runs. To discover if leaked 
    product has reached groundwater, these wells can be checked periodically by hand or 
    continuously with permanently installed equipment. This method is effective only at 
    sites where groundwater is within 20 feet of the surface. 
    More detailed information on groundwater monitoring.


  5. Statistical inventory reconciliation (SIR)
    SIR uses sophisticated computer software to determine whether a tank system is leaking. 
    The computer conducts a statistical analysis of inventory, delivery, and dispensing data 
    collected over a period of time and provided by the operator to a vendor. 
    More detailed information on statistical inventory control.


  6. Manual tank gauging
    Manual tank gauging can be used only on tanks 2,000 gallons or smaller. This method 
    does NOT work on tanks larger than 2,000 gallons or on piping. This method requires 
    taking the tank out of service for at least 36 hours each week to take measurements of 
    the tank's contents. Tanks 1,000 gallons or less can use this method alone. Tanks from 
    1,001 to 2,000 gallons can use this method only when it is combined with periodic tank 
    tightness testing and only for 10 years after installing a new UST or upgrading an UST 
    with corrosion protection. After 10 years, these USTs must use one of the leak detection 
    methods listed above in 1-5. 
    More detailed information on manual tank gauging.

    The additional method below can be used temporarily at petroleum UST sites:

  7. Tank tightness testing and inventory control
    This is a combination of two methods. Tank tightness testing requires periodic tests 
    conducted by vendors who temporarily install special equipment that tests the 
    soundness of the tank. Tank tightness testing must be used in combination with 
    inventory control. Inventory control requires taking daily accurate measurements of 
    the tank's contents and performing monthly calculations to prove that the system is not 
    leaking. Tank tightness testing and inventory control can be used only for 10 years after 
    installing a new UST or upgrading an UST with corrosion protection. After 10 years, these 
    USTs must use one of the leak detection methods listed above in 1-5. 
    More information on tank tightness testing combined with monthly inventory control.

What leak detection methods can you use to detect leaks from piping?

Pressurized piping must meet the following requirements: If your UST has suction piping, your leak detection requirements will depend on which type 
of suction piping you have.

Why might you fail to be in compliance even if you have the required leak 
detection equipment or method?

It takes more than equipment to be in compliance and to have a safe facility. You must operate 
and maintain this equipment properly over time or you will not benefit from having the 
equipment or using an approved leak detection method. Most importantly, you must be sure 
you successfully use the method at least once a month to determine if the UST system has 
released any of its contents.

Failure to operate and maintain equipment and methods can lead to new releases. For example, 
a poorly functioning ATG system will provide inaccurate data that will be useless in detecting 
leaks. A manual vapor or groundwater monitoring device that doesn't work properly means 
you have no reliable leak detection system. Inaccurate data from poorly operated and maintained 
measuring devices can make SIR methods unable to usefully detect leaks in a timely manner. 
If your leak detection fails, you may incur fines or penalties for noncompliance, as well as an 
expensive cleanup at your UST site.

Be sure you review and use the information sources on our 
Operating And Maintaining UST Systems Web pages.

Are reporting and recordkeeping necessary?

If operation of the leak detection method indicates a possible leak, UST owners and operators 
need to report the potential release to the regulatory authority. UST owners and operators must 
keep records
on leak detection performance and upkeep. These include the previous year's 
monitoring results, the most recent tightness test results, performance claims by the leak 
detection device's manufacturer, and records of recent maintenance and repair.

How can publications on leak detection help you?

To assist owners and operators in conducting proper leak detection, OUST has developed 
several publications that are available on our Web site for viewing, downloading, printing, 
or ordering. These publications clearly present leak detection requirements to UST owners 
and operators:
You may also want to use the following resources:

Many other publications are also available for viewing, downloading, printing, or ordering at 
OUST's publications page.