Automatic Tank Gauging Systems
How does the release detection method work?
This method uses automated processes to monitor product level and inventory control. A probe permanently installed in the tank is connected to a monitor to provide information on product level and temperature. These systems calculate changes in product volume that can indicate a leaking tank. Automatic tank gauging systems (ATG systems) operate in one of two modes: inventory mode and leak detection mode. In the leak detection mode, ATG systems can be set manually or automatically to perform a leak test. Manual leak tests are in-tank static tests and automatic leak tests are continuous in-tank leak detection tests. When we refer to ATG systems we are referring to testing performed in the in-tank static test mode. ATG systems operating in continuous in-tank leak detection test mode are covered under Continuous In-Tank Leak Detection.Features of ATG systems include:
- The product level and temperature in a tank are measured and recorded by a computer, this saves labor and time.
- In the inventory mode, the ATG system replaces the use of the gauge stick to measure product level and perform inventory control. This mode records the activities of an in-service tank, including deliveries.
- In the leak detection mode (in-tank static test), the tank is taken out of service and the product level and temperature are measured for at least one hour.
- Note: Some systems, known as continuous ATG systems, do not require the tank to be taken out of service to perform a test. This is because these systems can gather and analyze data during many short periods when no product is being added to or taken from the tank. These systems are discussed under Continuous In-Tank Leak Detection.
What are the regulatory requirements?
The ATG system must be able to detect a leak no larger than 0.2 gallon per hour with certain probabilities of detection and false alarm. Some ATG systems can also detect a leak of 0.1 gallon per hour with the required probabilities.
Beginning on [three years after effective date], you must perform the following, as applicable, on your release detection equipment annually to make sure it is working properly:
- Verify the system configuration
- Test alarm operability and battery backup
- Inspect probes and sensors for residual build-up
- Ensure floats move freely, the shaft is not damaged, and cables are free of kinks and breaks
- Keep records of these tests for three years
Testing must be performed in accordance with manufacturer’s requirements; a nationally recognized code of practice; or requirements determined by your implementing agency to be no less protective of human health and the environment.
Will it work at your site?
ATG systems have been used primarily on tanks containing gasoline or diesel. If considering using an ATG system for larger tanks or products other than gasoline or diesel, discuss its applicability with the manufacturer or installer.
Anything else you should consider?
- Detecting water in the tank is important. Water around a tank may mask a hole in the tank or distort the data to be analyzed by temporarily preventing a release. To detect a release in this situation, check for water at least once a month. Depending upon the product in the tank, detecting water may be difficult to do, but not impossible. Products such as ethanol-based fuels may not form a water bottom. An unexplained presence of water in the tank is considered an unusual operating condition. If you find water in your tank you must investigate and correct the source of the water. Suspected releases must be reported to the implementing agency within 24 hours, or period specified by the implementing agency.
- The ATG system probe is permanently installed through an opening (not the fill pipe) on the top of the tank. Each tank at a site must be equipped with a separate probe. The ATG system probe is connected to a monitor that displays ongoing product level information and the results of the monthly test. Printers can be connected to the monitor to record this information.
- ATG systems are often equipped with alarms for high and low product level, high water level, and theft.
- ATG systems can be linked with computers at other locations from which the system can be programmed or read.
- For ATG systems that are not of the continuous type, no product should be delivered to the tank or withdrawn from it for at least 6 hours before the monthly test or during the test (which generally takes 1 to 6 hours).
- An ATG system can be programmed to perform a test more often than once per month (a recommended practice).
Will you be in compliance?
For USTs installed [on or before 180 days after effective date], owners and operators may use ATG systems as their primary method of release detection. When installed and operated according to the manufacturer's specifications, ATG systems meet the federal release detection requirements. USTs installed or replaced after [180 days after effective date] may no longer use ATG systems (used solely for in-tank release detection) as the primary method of release detection. USTs must be secondarily contained and use interstitial monitoring.
View EPA's publication, Automatic Tank Gauging Systems for Release Detection: Reference Manual for Underground Storage Tank Inspectors, for information on evaluating how well UST owners and operators are using their ATG systems to comply with release detection requirements.