Tank tightness testing was once the ordinary way a UST proved it was sound. Monthly monitoring replaced it for most sites, and the question that remains is whether a tank with a working gauge on it owes a tightness test as well. Usually not. The cases where the answer flips are worth knowing, because they are the ones where somebody is about to spend money either way.
The standard: 0.1 gallons per hour, with five caveats
40 CFR 280.43(c) sets what the test has to achieve. It must be capable of detecting a 0.1 gallon per hour leak rate from any portion of the tank that routinely contains product.
Then it names the things the test has to account for while doing it: thermal expansion or contraction of the product, vapor pockets, tank deformation, evaporation or condensation, and the location of the water table.
That list is the reason a tightness test is a scheduled event with a contractor rather than a reading somebody takes. A tenth of a gallon an hour is a small enough signal that ordinary physics drowns it. Fuel delivered cold into a warm tank expands. A tank with a slight bow holds a different volume at different levels. Groundwater above the tank bottom changes the pressure across the shell. A method that ignores any of those produces a number, and the number means nothing.
Why the gauge gets a looser number
An automatic tank gauge is held to a different threshold. 280.43(d)(1) requires the automatic product level monitor test to detect a 0.2 gallon per hour leak rate. Twice as coarse as the tightness test.
The reason is frequency. The gauge runs every month, twelve times a year, every year. The tightness test resolved finer and historically ran once every few years. Repetition buys back the sensitivity: a 0.15 gallon per hour loss the gauge cannot resolve in one month tends to declare itself over several, and a slow loss large enough to matter does not stay hidden through a dozen consecutive tests.
Knowing which number belongs to which method is also how you read a contractor's quote honestly. A vendor offering a 0.2 gph method to satisfy a requirement written at 0.1 is offering the wrong test.
The clause most sites have aged out of
Tightness testing survives in the rule as an alternative for older tanks, and the window has closed on nearly all of them.
280.41(a)(1) requires tanks installed on or before April 11, 2016 to be monitored at least every 30 days, with an exception at (a)(1)(i): systems meeting the performance standards in 280.20 or 280.21 and the monthly inventory control requirements of 280.43(a) or (b) could use tank tightness testing at least every 5 years, until 10 years after the tank was installed.
Do the arithmetic on that and it applies to tanks installed in 2006 or later that were still inside their first decade. For tanks installed after April 11, 2016, 280.41(a)(2) requires monitoring at least every 30 days with no tightness testing alternative offered.
So for the great majority of operating sites, the honest answer to "do I still need a tank tightness test" is that the monthly method is the requirement and the tightness test is not part of the routine calendar.
When it is still the right test
The requirement fading from the periodic calendar does not make the test obsolete. It moves it from a scheduled item to a triggered one.
- After a repair. Work on the tank generally has to be demonstrated tight before the tank returns to service.
- After a suspected release. When an unexplained loss shows up, somebody has to establish whether the tank is the source, and a monthly method that produced the suspicion is not going to resolve it.
- Buying or selling. A precise result on a known date is exactly what a buyer, a lender or an environmental consultant wants, and it is cheap next to the liability it addresses.
- After a gap in monitoring. A console that was out of service for months leaves a hole in the record. A tightness test gives a clean baseline to start again from.
Connecticut's periodic testing table makes the same distinction in its notes: the table covers periodic testing, and says plainly it is not intended to cover initial testing, testing after a repair, or additional testing required after a suspected release or an unexpected loss or gain.
The trap in the word tightness
A tank tightness test covers the tank. Piping runs on its own requirement with its own numbers, in 280.41(b) and 280.44, and a line tightness test is a different test on a different schedule.
Two tests with nearly the same name, one for the vessel and one for the pipe. A record that says only "tightness test, passed, May" has not said which, and that ambiguity is worth removing while the person who ordered the work still remembers.
How FastDragon handles it
Tank tightness sits on the calendar only where the site profile puts it there, which for most sites means it is switched off with the reason recorded rather than absent. A site relying on monthly monitoring shows the monitoring, and the tightness item shows why it is quiet.
Where a test is triggered rather than scheduled, it is logged as a completed record against the tank with its report attached, so the history reads correctly years later when somebody is asked what the tank was doing before a sale. Tank and line tests are separate requirements with separate records, so neither can be filed as the other.
Common questions
I have an automatic tank gauge. Do I still need a tank tightness test?
For most sites, no, because the gauge running monthly is the release detection method and the tightness test was the alternative. The exception is narrow and time limited: 40 CFR 280.41(a)(1)(i) let systems meeting the performance standards in 280.20 or 280.21, plus monthly inventory control, use tank tightness testing every 5 years until 10 years after the tank was installed. Tanks installed after April 11, 2016 are monitored at least every 30 days with no tightness testing alternative.
How sensitive does a tank tightness test have to be?
It has to detect a 0.1 gallon per hour leak rate from any portion of the tank that routinely contains product, under 280.43(c). The rule also names five conditions the test has to account for while doing it: thermal expansion or contraction of the product, vapor pockets, tank deformation, evaporation or condensation, and the location of the water table.
Why is the ATG threshold 0.2 and the tightness test 0.1?
Because they run at different frequencies. 280.43(d) sets the automatic product level monitor at 0.2 gallons per hour, and it runs every month. The tightness test resolves twice as fine and historically ran once every few years. A coarser test done twelve times a year and a finer test done occasionally are two ways of covering the same risk.
Does Connecticut require a tank tightness test?
Its periodic testing table carries a tank tightness test column referencing RCSA 22a-449(d)-111(b)(2)(F), and it reads N/A for most tank categories with one exception. Read the table for your own tank category rather than assuming either answer, and remember the table is about periodic testing, not the initial testing or the testing required after a repair.
When would I choose a tightness test today?
After a repair, after a suspected release, when a tank is being bought or sold, or when a monitoring method has been out of service long enough that you want a clean baseline. Those are situations where somebody wants a precise answer about the tank on a specific date, which is what the test provides and what monthly monitoring does not.