Automatic Tank Gauging

How does the leak detection method work?

This method uses automated processes to monitor product level and inventory control. Overfill alarms are often a part of automatic tank gauging systems (ATGS). Overfill alarms use probes installed in the tank to activate an alarm (see illustration) when the tank is either 90 percent full or within 1 minute of being overfilled. Either way, the alarm should provide enough time for the driver to close the truck's shutoff valve before an overfill happens. Alarms must be located where the driver can see or hear them easily.

Overfill alarms work only if they alert the driver at the right time and the driver responds quickly. Remember to put the alarm on an electrical circuit that is active all the time so that the alarm will always work. Many deliveries are made at night when the facility is closed. You don't want to turn off your alarm when you turn off the office lights.

Features of ATGS include:

The product level and temperature in a tank are measured continuously and automatically analyzed and recorded by a computer--this saves labor and time.
In the "inventory mode," the ATGS 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 "test mode," the tank is taken out of service and the product level and temperature are measured for at least one hour. Some systems, known as "continuous ATGS," 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.

What are the regulatory requirements?

The ATGS must be able to detect a leak no larger than 0.2 gallons per hour with certain probabilities of detection and of false alarm. Some ATGS can also detect a leak of 0.1 gallons per hour with the required probabilities.

Will it work at your site?

ATGS have been used primarily on tanks containing gasoline or diesel, with a capacity of up to 15,000 gallons. If considering using an ATGS for larger tanks or products other than gasoline or diesel, discuss its applicability with the manufacturer's representative.

Water around a tank may hide a leak by temporarily preventing the product from leaving the tank. To detect a leak in this situation, the ATGS should be capable of detecting water in the bottom of a tank.

Anything else you should consider?

The ATGS 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 ATGS 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.
ATGS are often equipped with alarms for high and low product level, high water level, and theft.
ATGS can be linked with computers at other locations, from which the system can be programmed or read.
For ATGS 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 ATGS can be programmed to perform a test more often than once per month (a recommended practice).

Will you be in compliance?

When installed and operated according to the manufacturer's specifications, automatic tank gauging systems (ATGS) meet the federal leak detection requirements for new and existing USTs. A test performed each month fulfills the requirements for the life of the tank.

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 ATGS to comply with release detection requirements.