Underground Storage Tanks

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
Tanks 2 Choices	Monthly Monitoring*; 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 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. Automatic Shutoff Device -or- Flow Restrictor -or- Continuous Alarm System	-AND-	Set B. Annual Line Testing -or- Monthly Monitoring* (except automatic tank gauging)
Suction Piping 3 Choices	Monthly Monitoring* (except automatic tank gauging); or Line Testing Every 3 Years; or 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:

• Secondary Containment With Interstitial Monitoring
• Automatic Tank Gauging
• Monitoring For Vapors In The Soil
• Monitoring For Liquids On The Groundwater
• Statistical Inventory Reconciliation (SIR)
• Other Methods Approved by the Implementing Agency 

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 detailed 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:

• The 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 following monthly methods:
  • interstitial monitoring,
  • vapor monitoring,
  • groundwater monitoring,
  • statistical inventory reconciliation,
  • or other methods approved by the Implementing Agency.

If your UST has suction piping, your leak detection requirements will depend on which type of suction piping you have.

• If you determine that your suction piping has characteristics listed below, your piping 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 exactly match the characteristics noted above must have leak detection, either monthly monitoring (using one of the monthly methods noted above for use on pressurized piping) or tightness testing of the piping every 3 years. More information on leak detection for underground piping is available.

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:

• Operating And Maintaining UST Systems: Practical Help And Checklists (see sections on leak detection).
• Straight Talk On Tanks: Leak Detection Methods For Petroleum Underground Storage Tanks And Piping
• Doing Inventory Control Right For Underground Storage Tanks
• Introduction To Statistical Inventory Reconciliation For Underground Storage Tanks
• Manual Tank Gauging For Small Underground Storage Tanks
• Getting The Most Out Of Your Automatic Tank Gauging System

You may also want to use the following resources:

• Please visit the NWGLDE Web site for a variety of leak detection related information, which includes the most recent list of leak detection methods that have been evaluated by third parties to determine if they meet EPA's performance standards.
• EPA published Standard Test Procedures For Evaluating Various Leak Detection Methods that testers can use to demonstrate if a leak detection method meets federal UST requirements for detecting leaks.
• Refer to the UST Technical Compendium for questions and answers regarding release detection (RD) issues.

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

Top of page