General information only, last reviewed October 25, 2026. Full notice at the end of the page. A date on this page has passed. Check the current rule at the source before you rely on it. Dates to watch
Fuel sits in tanks underground where you cannot see it, so a station needs a way to know what is down there at all times. That is the job of the automatic tank gauge. It turns a buried tank into a live, recorded number, and it sits at the center of both inventory and leak detection. This guide covers how it works and why it matters.
What an ATG is
An automatic tank gauge is an electronic system that continuously monitors an underground fuel tank. A probe in the tank measures fuel level, water, and temperature, and a console reads it out, tracks inventory, and runs leak-detection tests. It replaces the old manual stick reading with a constant, logged picture of the tank.
How it works
A probe inside the tank senses the fuel and water levels (commonly with a float or magnetostrictive sensor) along with temperature. The console converts those readings into gallons, records them over time, and can run automated leak tests during quiet hours when fuel is not moving.
What it measures
- Fuel volume. How many gallons are in the tank right now.
- Water level. Water at the tank bottom, a problem to catch early.
- Temperature. Needed to correct volume, since fuel expands and contracts.
Its role in compliance
The ATG is usually the heart of a station's leak detection. EPA underground storage tank rules require release detection, and the ATG console runs the automated tests and keeps the records that prove it.
The rule sets the gauge a number. 40 CFR 280.43(d)(1) requires the automatic product level monitor test to detect a 0.2 gallon per hour leak rate from any portion of the tank that routinely contains product. That is deliberately looser than the 0.1 gallon per hour tank tightness test, because the gauge runs every month where the tightness test ran once every few years.
The annual certification
Contractors usually invoice this as an ATG certification. The rule calls it a test of proper operation, and 40 CFR 280.40(a)(3) requires it at least annually. A state that runs its own approved UST program can require more. For the console and its controllers it means three things: test the alarm, verify the system configuration, and test the battery backup. Probes and sensors carry their own list, including that floats move freely, the shaft is undamaged, cables are free of kinks and breaks, and the alarm communicates with the controller.
Verify system configuration means somebody confirms the console is set up for the tanks that are actually in the ground, which catches the site where a tank was replaced and the console still holds the old capacity. A gauge running perfectly against the wrong tank profile produces confident numbers that are wrong.
280.45(b)(1) requires the annual operation test record to be held three years and to list each component tested, say whether it met the criteria or needs action, and describe what was done about anything that did not. There is more on what the annual operability test covers and on how long each record is kept.
ATG and wet stock
The ATG and wet stock reconciliation are a team. The ATG measures what is physically in the tank; reconciliation compares that against what your books say you bought and sold. The gauge gives you a trustworthy reading, and reconciliation turns it into an early warning when the numbers drift apart.
Where FastDragon fits
A live tank reading only pays off if it flows into your books and gets compared to your sales. FastDragon brings tank and sales data together so a variance surfaces while it is still small, turning the ATG's numbers into action.
Questions we hear a lot
Who makes ATG systems?
The consoles most stations run are Veeder-Root's TLS series, OPW's SiteSentinel, and Franklin Fueling's EVO line. Back-office and tank-monitoring software can poll any of the major consoles, so the brand matters less than keeping the probes and sensors tested.
What leak rate does an ATG have to detect?
EPA's monthly monitoring standard for automatic tank gauges, in 40 CFR 280.43(d), requires detecting a leak of 0.2 gallons per hour. An ATG meets it with in-tank static tests or continuous statistical leak detection. The tighter 0.1 gallon-per-hour tightness test is a separate procedure used in specific situations.
Do ATG readings replace stick readings?
Mostly. The probe is the daily source of truth, and it never forgets to take a reading. Many operators still stick tanks now and then to cross-check the probe, and some state inspectors ask for manual reconciliation records, so the gauge stick has not fully retired.
Why does the water reading matter?
Water settles under the fuel, where it corrodes steel tanks, feeds microbial growth in diesel, and in ethanol blends can cause phase separation that ruins the product. A rising water reading can also mean a breach letting groundwater in, so it deserves the same attention as the gallons.
Sources: 40 CFR 280.40, 280.43 and 280.45; state programs under 40 CFR 281.12.