Release Detection for Underground Storage Tanks (USTs) - Introduction
Because detecting UST systems releases quickly helps stop contamination before it spreads from UST sites, EPA requires owners and operators detect releases from their UST systems. EPA allows three categories of release detection: interstitial, internal, and external. These three categories include seven release detection methods.
- Why is release detection crucial?
- What release detection methods can you use to detect leaks from tanks?
- What release detection methods can you use to detect leaks from piping?
- Why might you fail to be in compliance even if you have the required release detection equipment or method?
- What additional operation and maintenance activities will you need to do for your release detection?
- Are reporting and recordkeeping necessary?
- What additional records will you need to keep?
- What will you have to do to meet the release detection requirements for previously deferred UST systems?
- What are the piping release detection requirements?
- What are the tank release detection requirements?
- How can publications on leak detection help you?
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:
- You can detect a leak from any portion of the tank or its piping that routinely contains petroleum; and
- Your leak detection is installed and calibrated in accordance with the manufacturer's instructions.
The leak detection requirements are summarized in the table below:
Notes: Release detection requirements for previously deferred UST systems are discussed here. Monthly means at least once every 30 days.
| UST System Component | Release Detection Method | ||
|---|---|---|---|
| Tanks 2 Choices for tanks installed on or before April 11, 2016 |
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| Tanks installed or replaced after April 11, 2016 |
Secondary Containment with Interstitial Monitoring | ||
| Pressurized Piping Choice of one from each set A & set B for piping installed on or before April 11, 2016: |
Set A. Use an automatic line leak detector that:
|
-and- | Set B.
|
| Pressurized Piping installed or replaced after April 11, 2016: |
Use an automatic line leak detector that:
-AND- Secondary Containment with Interstitial Monitoring |
||
| Suction Piping 3 Choices for piping installed on or before April 11, 2016 |
|
||
| Suction Piping installed or replaced after April 11, 2016 |
|
||
*Monthly monitoring choices in the table above include:
- Interstitial method – secondary containment with interstitial monitoring; secondary containment and under-dispenser containment
- Internal methods – automatic tank gauging (ATG) systems; statistical inventory reconciliation (SIR); continuous in-tank leak detection
- External method – monitoring for vapors in the soil; monitoring for liquids on the groundwater
- 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 meet all the requirements of this method).
What release detection methods can you use to detect leaks from tanks?
Owners and operators of petroleum USTs installed on or before April 11, 2016 must use at least one of these leak detection methods, or other methods approved by their implementing agency.
Interstitial Method
For USTs installed or replaced after April 11, 2016 owners and operators must use secondary containment with interstitial monitoring.
Internal Methods
- Automatic tank gauging (ATG) systems
- Manual tank gauging
- Statistical inventory reconciliation (SIR)
- Continuous in-tank leak detection (CITLD)
The additional method below can be used temporarily at petroleum UST sites:
External Methods
What release detection methods can you use to detect leaks from piping?
Pressurized piping installed on or before April 11, 2016 must meet the following requirements:
- The piping must have devices that automatically shut off or restrict flow or triggers 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:
If your UST has suction piping that is installed on or before April 11, 2016 your release detection requirements will depend on which type of suction piping you have.
- If you can show that your suction piping has characteristics listed below, your piping will not need release 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 release 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.
Piping installed or replaced after April 11, 2016 must have secondary containment with interstitial monitoring, except suction piping that has characteristics listed above. In addition, pressurized piping must have a device that automatically shuts off or restricts flow or triggers an alarm that indicates a leak.
What are the regulatory requirements for suction piping?
- No leak detection is required if the suction piping has the following characteristics:
- the piping has enough slope so that the product in the pipe can drain back into the tank when suction is released, and
- the piping has only one check valve, which is as close as possible beneath the pump in the dispensing unit.
- if a suction line is to be considered exempt based on these design elements, there must be some way to check that the line was actually installed according to these plans, that is those elements of #1 and #2 must be easily discernable.
- If a suction line does not meet all of the design criteria noted above, one of the following leak detection methods must be used:
- A line tightness test at least every 3 years; or
- Monthly interstitial monitoring; or
- Monthly vapor monitoring; or
- Monthly groundwater monitoring; or
- Monthly statistical inventory reconciliation.
The line tightness test must be able to detect a leak at least as small as 0.1 gallon per hour with certain probabilities of detection and of false alarm.
Interstitial monitoring, vapor monitoring, groundwater monitoring, and statistical inventory reconciliation have the same regulatory requirements for piping as they do for tanks. See the Leak Detection Requirements Table for more information.
What are the regulatory requirements for pressurized piping?
Each pressurized piping run must have one leak detection method from each set (A and B) below:
A. An Automatic Line Leak Detector:
- Automatic flow restricter; or
- Automatic flow shutoff; or
- Continuous alarm system.
B. And One Other Method:
- Monthly interstitial monitoring; or
- Monthly vapor monitoring; or
- Monthly groundwater monitoring; or
- Monthly statistical inventory reconciliation; or
- Annual tightness test.
- The automatic line leak detector (LLD) must be designed to detect a leak at least as small as 3 gallons per hour at a line pressure of 10 pounds per square inch within 1 hour by shutting off the product flow, restricting the product flow, or triggering an audible or visual alarm.
- The line tightness test must be able to detect a leak at least as small as 0.1 gallon per hour when the line pressure is 1.5 times its normal operating pressure. The test must be conducted each year. If the test is performed at pressures lower than 1.5 times operating pressure, the leak rate to be detected must be correspondingly lower.
- Automatic LLDs and line tightness tests must also be able to meet the federal regulatory requirements regarding probabilities of detection and false alarm.
- Interstitial monitoring, vapor monitoring, groundwater monitoring, and statistical inventory reconciliation have the same regulatory requirements for piping as they do for tanks. See the Leak Detection Requirements Table for more information.
How do the release detection methods for pressurized piping work?
Automatic line leak detectors (LLDs)
- Flow restrictors and flow shutoffs can monitor the pressure within the line in a variety of ways: whether the pressure decreases over time; how long it takes for a line to reach operating pressure; and combinations of increases and decreases in pressure.
- If a suspected leak is detected, a flow restricter keeps the product flow through the line well below the usual flow rate. If a suspected leak is detected, a flow shutoff completely cuts off product flow in the line or shuts down the pump.
- A continuous alarm system constantly monitors line conditions and immediately triggers an audible or visual alarm if a leak is suspected. Automated interstitial line monitoring system can be set to operate continuously and sound an alarm, flash a signal on the console, or even ring a telephone in a manager's office when a leak is suspected.
- Both automatic flow restrictors and shutoffs are permanently installed directly into the pipe or the pump housing.
- An automated interstitial monitoring system can be combined with an automatic shutoff system so that whenever the system detects a suspected release, the product flow in the piping is completely shut down. Under other methods in 40 CFR § 280.43(i)(2), EPA recognizes such a setup would meet the monthly monitoring requirement as well as the automatic line leak detector requirement. The following conditions must be met:
- Sump sensors used for piping interstitial monitoring must remain as close as practicable to the bottom of interstitial spaces being monitored.
- Monthly monitoring records must be maintained for at least one year.
- Electronic and mechanical components of the system, including shutoff devices, sensors, pressure or vacuum monitors, must be tested annually for proper operation Records of the test must be maintained for three years.
- Containment sumps that are part of the piping interstitial monitoring system must be tested at least once every three years for liquid tightness.
Line tightness testing
- Tracer methods do not measure pressure or flow rates of the product. Instead they use a tracer chemical to determine if there is a hole in the line. With tracer methods, all of the factors below may not apply.
- The line is taken out of service and pressurized, usually above the normal operating pressure. A drop in pressure over time, usually an hour or more, suggests a possible leak.
- Suction lines are not pressurized very much during a tightness test (about 7 to 15 pounds per square inch).
- Most line tightness tests are performed by a testing company. You just observe the test.
- Some tank tightness test methods can be performed to include a tightness test of the connected piping.
- For most line tightness tests, no permanent equipment is installed.
- In the event of trapped vapor pockets, it may not be possible to conduct a valid line tightness test. There is no way to tell definitely before the test begins if this will be a problem, but long complicated piping runs with many risers and dead ends are more likely to have vapor pockets.
- Some permanently installed electronic systems (such as some Automatic Tank Gauging Systems) can meet the requirements of a line tightness test.
Secondary containment with interstitial monitoring
- A barrier is placed between the piping and the environment. Double walled piping or a leakproof liner in the piping trench can be used.
- A monitor is placed between the piping and the barrier to sense a leak if it occurs. Monitors range from a simple stick that can be put in a sump to see if a liquid is present, to continuous automated systems, such as those that monitor for the presence of liquid product or vapors.
- Proper installation of secondary containment is the most important and the most difficult aspect of this leak detection method. Trained and experienced installers are necessary.
- See the information on secondary containment for additional information. Secondary containment for piping is similar to that for tanks.
Vapor or ground water monitoring
- Vapor monitoring detects product that leaks into the soil and evaporates.
- Groundwater monitoring checks for leaked product floating on the groundwater near the piping.
- A site assessment must be used to determine monitoring well placement and spacing.
- UST systems using vapor or groundwater monitoring for the tanks are well suited to use the same monitoring method for the piping.
- See the information on vapor monitoring and groundwater monitoring for more information. Use of these methods with piping is similar to that for tanks.
Why might you fail to be in compliance even if you have the required release 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 acceptable 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.
Please review and use the information on our Resources for Owners and Operators Web pages.
What additional operation and maintenance activities will you need to do for your release detection?
For tank release detection:
Beginning on October 13, 2018 as part of the walkthrough inspection requirement, at least every 30-days, you must:
- Check to make sure the release detection equipment is operating with no alarms or other unusual operating conditions present; and
- Ensure records of release detection testing (includes monthly monitoring) are reviewed and current.
Annually, you must:
- Check hand held release detection equipment such as tank gauge sticks and ground water bailers for operability and serviceability.
Beginning on October 13, 2018 you must annually test operability of mechanical and electronic release detection equipment such as your automatic tank gauge, probes and sensors, and make sure it is working properly. Information on the minimum equipment that must be tested is provided in the more detailed information links associated with the individual release detection methods above.
For piping release detection:
Beginning on October 13, 2018 as part of the walkthrough inspection requirement and at least every 30 days, you must:
- Check to make sure the devices you are using that automatically shut off or restrict flow of product or triggers an alarm to indicate a leak are operating with no alarms or other unusual operating conditions present; and
- Ensure records of testing these devices are reviewed and current.
Annually, you must:
- Visually check containment sumps with interstitial monitoring for damage, leaks to the containment area, or releases to the environment;
- Check double walled sumps with interstitial monitoring for a leak in the interstitial area.
Beginning on October 13, 2018 you must annually test operability and determine devices you are using to automatically shut off or restrict flow or triggers an alarm to indicate a leak in your piping meet the 3 gallons per hour at 10 pounds per square inch line pressure within one hour performance standard by simulating a leak. Operability of mechanical and electronic components such as suction pumps of suction systems must also be tested annually to ensure they are operating as required.
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.
What additional records will you need to keep?
Beginning on October 13, 2018, you must also keep these records:
- Operation and maintenance walkthrough inspections that are required for periods of at least every 30 days and annually for one year;
- Release detection equipment that is tested annually to ensure proper operation for three years; and
- If you store regulated substances containing greater than 10 percent ethanol or greater than 20 percent biodiesel, or any other regulated substance identified by the implementing agency, you must keep records demonstrating compatibility of the release detection components in contact with the regulated substances, for as long as the UST system stores the regulated substance.
Click here for more information on compatibility requirements.
What will you have to do to meet the release detection requirements for previously deferred UST systems?
The 2015 UST regulation removes the deferral for UST systems that store fuel solely for use by emergency power generators (emergency generator tanks); field-constructed tanks (FCTs); and airport hydrant fueling systems (AHSs). Owners and operators of these systems must meet release detection requirements described below within the time-frames stated for each type of UST system.
Emergency generator tanks
These UST systems must meet release detection requirements as follows:
- Systems installed on or before October 13, 2015 have three years to use any of the applicable release detection methods listed above.
- Systems installed between October 13, 2015 and April 11, 2016 must use any of the applicable release detection methods listed above at installation.
- Systems installed or replaced after April 11, 2016 must meet secondary containment requirements with interstitial monitoring.
EPA recognizes the optional use of an Automated Interstitial Monitoring (AIM) system as meeting the federal pressurized piping release detection requirements. EPA provided an in-depth technical discussion of these systems and an introduction to owners and operators, respectively, in these two publications:
- In-Depth Discussion: Automated Interstitial Monitoring Systems for Underground Pressurized Piping on Emergency Power Generator UST Systems (EPA 510-K-22-002). May 2022.
- Owner and Operator Introduction: Automated Interstitial Monitoring Systems for Underground Pressurized Piping on EPG UST Systems (EPA 510-K-22-001). May 2022.
To help owners and operators complete submitting certification of compliance for their AIM systems to their UST implementing agencies and meet periodic inspection and testing requirements, owners and operators may use the interactive PDF forms provided by EPA. These forms are available through this link:
EPA responded to several questions about release detection and general issues pertaining to emergency power generator UST systems. See the emergency power generator UST systems related questions and answers provided in the UST Technical Compendium about the 2015 Federal UST Regulations.
Field constructed tanks (FCTs) and airport hydrant systems (AHSs)
A general outline of the release detection requirements for FCTs and AHSs is provided below. Owners and operators must meet release detection requirements identified below.
FCTs and AHSs installed on or before October 13, 2015, must have release detection by October 13, 2018. FCTs and AHSs installed after October 13, 2015 must meet all release detection requirements at installation. Tanks and some piping installed after April 11, 2016 must be secondarily contained and use interstitial monitoring. Owners and operators may use single walled piping when installing or replacing piping associated with UST systems with field-constructed tanks greater than 50,000 gallons and piping associated with airport hydrant systems.
What are the piping release detection requirements?
Underground piping associated with FCTs less than or equal to 50,000 gallons must use the conventional piping release detection options described above. Remember, piping associated with these size FCTs installed after April 11, 2016 must be secondarily contained and use interstitial monitoring.
Underground piping associated with all AHSs and those FCTs greater than 50,000 gallons must meet release detection requirements by using either the conventional piping release detection options described above (except underground piping using conventional groundwater and passive vapor monitoring must combine that method with inventory control as described below); or one of these four alternatives:
- Line tightness testing (at varying leak rates based on line segment volume)
- Perform a semiannual or annual line tightness test at or above operating pressure according to a maximum leak detection rate per test section volume.
- Leak detection rates range from 0.5 to 1.5 gallons per hour (gph) for annual line tightness test; and 1.0 to 3.0 gph for semiannual line tightness test.
Piping segment volumes greater than or equal to 100,000 gallons not capable of initially meeting the 3 gallons per hour leak rate for semiannual testing may be tested at a leak rate up to 6 gallons per hour leak rate for a limited time. The first test, at a leak rate up to 6.0 gph, must be conducted not later than October 13, 2018. The second test, also at a leak rate up to 6.0 gph, must be conducted between October 13, 2018 and October 13, 2021. The third test, at a leak rate up to 3.0 gph, must be conducted between October 13, 2021 and October 13, 2022. Subsequent tests after October 13, 2022 would be performed semiannually or annually at the appropriate leak rates according to line segment volumes.
- Active vapor monitoring (using chemical tracers)
- Inventory control with biennial tightness testing, or groundwater or passive vapor monitoring (monitoring stored regulated substance)
- Another method approved by the implementing agency
What are the tank release detection requirements?
Underground storage tanks associated with AHSs and FCTs with a capacity less than or equal to 50,000 gallons must be monitored using any of the conventional tank release detection options described above. Remember, tanks less than or equal to 50,000 gallons installed after April 11, 2016 must be secondarily contained and use interstitial monitoring.
FCTs with a capacity greater than 50,000 gallons must be monitored either using any of the conventional tank release detection methods above or use one of the alternatives listed below. An exception is that underground storage tanks using conventional groundwater and passive vapor monitoring must combine that method with inventory control as described below:
- Tank tightness testing
- ATG systems with tank tightness testing (two options)
- Active vapor monitoring (using chemical tracers)
- Inventory control with biennial tightness testing, or groundwater or passive vapor monitoring (monitoring stored regulated substance)
- Another method approved by the implementing agency
How can publications on release detection help you?
To assist owners and operators in conducting proper leak detection, EPA developed several publications that are available on our website for viewing, downloading, printing, or ordering. These publications clearly present leak detection requirements to UST owners and operators:
- Release Detection for Underground Storage Tanks and Piping: Straight Talk on Tanks
- Operating and Maintaining UST Systems: Practical Help and Checklists (see sections on leak detection).
- 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 website 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 EPA's UST publications page.