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UST release detection internal methods


Detecting underground storage tank (UST) system releases fast helps to stop contamination before it spreads from UST locations. Due to this, the Environmental Protection Agency (EPA) mandates owners and operators to detect releases from their UST systems. Release detection is important to prevent fires and explosions. It also helps to prevent releases from harming groundwater resources that people rely on for drinking. Three different categories of release detection are permitted: interstitial, internal, and external. This Fact File focuses on internal methods of UST release detection. Presented here is information on automatic tank gauging (ATG) systems, manual tank gauging, statistical inventory reconciliation (SIR), and continuous in-tank leak detection (CITLD). Each will be explained.


A UST is a tank and any underground piping connected to the thank that has at a minimum 10% of its joint volume underground. Federal UST regulations are applicable only to UST systems storing petroleum or certain hazardous substances. Most regulated USTs contain petroleum. UST owners may be marketers who sell gasoline to the public or non-marketers who use tanks for their own needs like fleet service operators. UST regulations have been separated into three sections: technical requirements, financial responsibility requirements, and state program approval purposes. Release reduction and leak detection of USTs fall into the technical requirements.

Automatic tank gauging

ATG is an internal method that uses automated processes to watch product level and inventory control. There is a permanently installed probe in the tank that is linked to a monitor to offer information on product level and temperature. These systems calculate product volume changes that can indicate a leaking tank. ATG systems operate in one of two manners. This includes inventory manner or leak detection manner. In the leak detection manner, ATG systems can be set manually or automatically to perform a leak test. Manual leak tests are in-tank static tests. While automatic leak tests are continuous in-tank leak detection tests. These systems have mainly been used on tanks with gasoline or diesel.

Manual tank gauging

Manual tank gauging is another internal method that involves keeping the tank undisturbed for at least 36 hours each week. During this time, the tank's contents are measured, twice at the start and twice at the end of the test period. Manual tank gauging can be used as the only method of leak detection for the life of the tank only for tanks as large as 1,000 gallons. Tanks between 1,001 and 2,000 gallons can use this method only with tank tightness testing. But note that this combined method, can be used only during the initial 10 years after tank installation. Manual tank gauging is low-cost. It can be an effective leak detection method when used with tanks of the apposite size.

Statistical inventory reconciliation

For SIR, a trained expert uses computer software to carry out a statistical analysis of inventory, delivery, and dispensing data. Both of you collect and supply this data to the vendor on a routine basis.

SIR internal methods are set apart from continuous in-tank leak detection methods by how inventory, delivery, and dispensing data are processed and provide a determination of the release status of the tank (or piping). SIR data are processed often involving a distinct analysis. This is performed by an SIR vendor or SIR software. Continuous statistically based in-tank release detection methods process data in a nonstop or almost nonstop way. SIR has been used mainly on tanks with a capacity of no more than 18,000 gallons.

Continuous in-tank leak detection

The final internal method of release detection for USTs is CITLD. It includes all statistically based methods where the system incrementally gathers measurements on a nonstop or almost nonstop basis to govern a tank’s leak status. There are two major groups that fit into this category: continuous statistical release detection and continual reconciliation. Both groups usually use permanently installed sensors in the tank to gain inventory measurements. They are combined with a microprocessor in the ATG system or other control console that processes the data. Continual reconciliation methods are set apart by their connection to dispensing meters that supply automatic recording and use of dispensing data in examining tank leak status. Continuous in-tank leak detection methods may allow for monitoring greater tank volumes and higher system throughputs.

Applicable laws & regulations

40 CFR 280 — Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks (UST)

40 CFR 282 — Approved Underground Storage Tank Programs

Related defintions

Interstitial method means a method that detects leaks in the area between the UST and a second barrier.

Microprocessor means a computer processor with memory and associated circuits contained on an integrated-circuit chip.

Key to remember

Along with the four methods described, there is tank tightness testing to consider. When performed along with the manufacturer's conditions, periodic tank tightness testing together with monthly inventory control can briefly meet the federal leak detection requirements for tanks. Note that this method does not detect piping leaks. Inventory control by itself does not meet the federal requirements for tank leak detection.

Real world example

Failure to adhere to UST regulations can come at a high price. A gas station and convenience store located in South Burlington, Vermont was fined a $35,000 penalty to the state due to a gasoline leak from an underground storage tank in 2006. The leak caused contamination of soil and groundwater near the gas station. The company did not learn their lesson and was fined again in 2017, for an incident at another location. This time, they were fined $6,750 for failing to conduct weekly leak detection monitoring for their three permitted 8,000-gallon underground storage tanks. During a routine visit it was revealed that the leak detection records showed invalid or failing in-tank leak test results.

They made costly mistakes more than once and paid the price for it. Make sure to learn from this company’s mistakes and implement and maintain proper release detection methods so you don’t get fined a dime.