There are several release detection options UST facilities may use. Selecting types of release detection systems may depend on cost, construction, tank age, tank size, ability, and ownership. 

The most common release detection systems include:

• Automating tank gauging (ATG)
• Statistical inventory reconciliation (SIR)
• Continuous in-tank leak detection (CITLD)
• Secondary containment (interstitial) monitoring
• Groundwater monitoring
• Vapor monitoring
• Manual tank gauging

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) operate in one of two modes: inventory mode and leak detection mode. In the leak detection mode, the ATG 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 ATGs, we are referring to testing performed in the in-tank static test mode. ATGs operating in continuous in-tank leak detection test mode are covered under Continuous Statistical Leak Detection.

For statistical inventory reconciliation (SIR), typically a trained professional uses sophisticated computer software to conduct a statistical analysis of inventory, delivery, and dispensing data. The UST owner or operator collects and supplies these data to the vendor on a regular basis.

Continuous in-tank leak detection (CITLD) is another form of leak detection conducted via an automatic tank gauge. This method encompasses all statistically based methods where the system incrementally gathers measurements on an uninterrupted or nearly uninterrupted basis to determine a tank’s leak status.

This method means the tank and piping have an inner and outer barrier with an interstitial space that is monitored for leaks. The regulations describe general performance requirements for interstitial monitoring with double-walled USTs, USTs fitted with internal liners, and USTs using interception barriers.

This method monitors the groundwater table (top level of water found underground) near a UST for the presence of released free product. Monitoring wells near the UST are checked frequently to see if petroleum can be detected. The regulation describes several requirements for the use of this method. For example, this method cannot be used if the water table is more than 20 feet below the ground's surface.

This method samples for either product vapors in the soil gas surrounding the UST (sometimes called passive monitoring) or the presence of a tracer compound introduced into the UST system (sometimes called active monitoring). Leaked petroleum produces vapors that can be detected in the soil gas. The presence of a tracer compound outside of the UST system is an indication of a suspected release. UST regulation describes several requirements for using this release detection method. For example, this method requires using porous soils in the backfill and locating the monitoring devices in these porous soils near the UST system | View Regulation >

This method involves keeping the tank undisturbed for at least 36 hours each week, during which the tank's contents are measured, twice at the beginning and twice at the end of the test period. Manual tank gauging can be used as the sole method of release detection for the life of the tank only for tanks up to 1,000 gallons. Tanks between 1,001 and 2,000 gallons that meet diameters identified in the U.S. EPA Table of Test Standards for Manual Tank Gauging can use this method only in combination with tank tightness testing. This combined method, however, can be used only during the first 10 years following tank installation | View Table >

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