UST Technical Compendium Category 3: Release Detection (RD)
These interpretations and guidance are based on the 1988 UST regulation.
EPA revised the UST regulations in June 2015. Some of the information in this compendium may no longer apply because of those revisions.
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Question 1: Please clarify EPA's UST regulations as they
apply to a threshold value for declaring an UST or its piping to be leaking
using a tightness test.
[November 11, 1988 letter from Jack Horner of Horner Creative Products, Inc.]
Answer: To be able to detect a 0.1 gallon per hour (gph)
leak as required in the regulations at a statistically reliable level of
confidence, the threshold must be smaller than 0.1 gph. The correct threshold
depends on the particular leak detection system and UST system, but is
traditionally and typically 0.05 gph.
[December 19, 1988 letter to Mr. Horner (PDF) (2 pp, 11K)]
Question 2: Is annual line testing required if a pressurized
line is equipped with a permanent line monitoring device?
[June 1989 letter from Judith Spray of Pollulert Systems]
Answer: If an automatic line monitoring device meets the
regulatory standard for a line tightness test, 0.1 gallon per hour at 1.5
times operating pressure, then it can be substituted for an annual line
tightness test. Note that here are also ways to comply that do not
involve line tightness testing.
[June 29, 1989 letter to Ms. Spray (PDF) (2 pp, 10K)]
Question 3: How do you convert a leak rate at one
operating pressure to an equivalent leak rate at another pressure?
[February 1990 letter from Michael Bouton of Tracer Research Corporation]
Answer: The appropriate formula for the conversion is
that the leak rate is proportional to the square root of the pressure drop
[February 28, 1990 letter to Mr. Bouton (PDF) (1 pg, 9K)]
Question 4: Do pressurized lines at UST sites that have
monitoring wells around tank pits, but not along piping runs, also have
to have an annual line pressure test?
[June 29, 1990 letter from Bill Birdwell of Tanknology Corporation International]
Answer: Pressurized lines must have automatic catastrophic
leak detection backed-up by a monthly monitoring or annual line tightness
test. If a tank excavation is intercepted by observation wells, but a pressurized
line system extends beyond the designed reach of those monitoring wells,
then an annual line tightness test or monthly monitoring is required.
[July 19, 1990 letter to Mr. Birdwell (PDF) (2 pp, 9K)]
Question 5: Can statistical inventory reconciliation (SIR)
be used to comply with EPA's UST regulations, including requirements for
[April 10, 1991 letter from Deborah Talanian of Entropy Limited]
Answer: SIR is generally a "tank system" test. Thus, if
properly performed for any particular site, a SIR method that demonstrated
adequate performance under the EPA evaluation protocols may be an acceptable
alternative to periodic line tightness testing. The line still must have
a catastrophic line leak detector, however.
[May 10, 1991 letter to Ms. Talanian (PDF) (2 pp, 9K)]
Answer: EPA has determined it is protective of human health
and the environment to be somewhat flexible about what portion of the upper
part of the tank must be tested so that UST owners and operators can take
full advantage of the different types of leak detection available. The
"routinely contains product" language is intended to make clear that test
methods do not have to test vent pipes, fill pipes, and fittings on top
of the tank. Some simple rules of thumb about how far below these parts
of the tank can be tested: (1) acoustic methods and SIR methods should
not be a concern, as to the level tested; (2) ATG level-sensing methods
should only be tested down the level at which the method was third-party
evaluated; (3) major in-tank level monitoring service providers most often
specify 85 to 95 percent full as their own protocol for testing and this
is seen as meeting the routinely contains product provision; and (4) small
business tanks with low product sales may test well below the top of the
tank, if inventory data demonstrates restricted tank in filling practices
that result in routinely low levels in the tank.
[July 25, 1991 memorandum to Region VIII (PDF) (3 pp, 13K)]
[June 26, 1991 Attachment (PDF) (1 pg, 9K)]
Question 7: Can manual tank gauging be used as the sole
method of leak detection for tanks larger than 550 gallons?
[January 22, 1990 from Priscilla Young of the American Petroleum Institute]
Answer: When conducted in accordance with the procedures
described in the attachment, manual tank gauging meets the performance
specifications under 40 CFR 280.43(h)(1) for tanks of nominal capacity
of 1000 gallons or less and, therefore, can be used as the sole means
of leak detection.
[April 6, 1990 letter to Ms. Young (PDF) (2 pp, 9K)]
Answer: As requirements for automatic line leak detectors
(LLDs), LLDs must be tested annually in accordance with manufacturer's
requirements but not necessarily tested to any particular leak rate. The
standard of 3 gallons per hour at 10 pounds per square inch within 1 hour
is not the standard for the annual test but rather for the initial performance
[March 5, 1992 memorandum to Regional Program Managers (PDF) (13 pp, 38K)]
Question 9: Do systems incorporating flexible liners
(bladders) and vacuum monitor systems meet the technical requirements?
[March 19, 1992 letter from John Hendershot of World Enviro Systems]
Answer: Flexible internally-fitted liner systems can be
shown to meet the Federal requirements for release detection for both petroleum
and hazardous substance USTs if certain conditions are met, including compatibility
and automatic detection of a breach in either the outer tank or the inner
liner. These systems cannot meet Federal requirements for upgrading or
repairing existing UST systems.
[July 9, 1992 letter to Mr. Hendershot (PDF) (4 pp, 18K)]
Question 10: Please clarify whether
the Federal underground storage tank regulations at 40 CFR 280.43 require
inventory control with automatic tank gauges (ATGs).
[October 2, 1992 letter from Mr. Durgin of Veeder Root to David Ziegele (PDF) (1 pg, 6K)]
Answer: Inventory control is not required, regardless
of the installation date, if the ATG has been shown to meet the performance
standard and the probabilities of detection and of false alarm.
[November 22, 1993 to Mr. Culp (PDF) (2 pp, 12K)]
[April 18, 1989 Attachment (PDF) (1 pg, 8K)]
Question 11: If a facility is using statistical inventory reconciliation (SIR) monthly and a report is not conclusive, is the owner/operator out of compliance?
Answer: Yes, an UST system relying on monthly SIR with
a report that does not conclusively indicate whether the system is leaking
at 0.2 gallons per hour with a probability of detection of 0.95 and a probability
of false alarm of 0.05 is not technically compliance with the release detection
requirements. A lack of conclusive results may not be possible on a small
percentage of tank data each month, for several reasons. Because
of this, EPA encourages States and Regions to use discretion, and to consider
the efforts of owners and operators to comply in assessing whether or not
enforcement is carried out.
[November 18, 1993 memorandum to State and Regional Program Managers (PDF) (2 pp, 11K)]
[February 7, 1994 letter to Mr. Hunt (PDF) (3pp, 14K)]
Question 12: Request that EPA require siphon bars that
join manifolded tank systems to be regulated with respect to leak detection
and corrosion protection, and that inventory control not be an acceptable
means of leak detection for a manifolded system.
[May 23, 1994 letter from Dale Tanke of the Office of the Illinois State Fire Marshal to Gerald Phillips, US EPA Region V.]
Answer: Siphon bars are already regulated in terms of leak detection and cathodic protection requirements as part of connected underground piping that routinely contains product. Due to the manner in which the syphons routinely operate, however, leak detection requirements are minimal, akin to that of safe suction lines.
As to leak detection with manifolded tanks, inventory control with periodic
tightness testing is permissible until December 22, 1998 or until ten years
subsequent to a new tank installation or upgrade.
[February 13, 1995 letter to Mr. Tanke (PDF) (3 pp, 13K)]
Question 13: In changing over from one form of leak detection
to another, is it necessary to finish up a twelve-month cycle with the
old method in order to be in compliance?
[October 4, 1994 letter from Robert Staab of the Circle K Corporation]
Answer: Changing from on acceptable leak detection method
to another can be done at any time. It does not require the completion
of a "cycle." However, it is important that all leak detection records
are properly maintained in accordance with 40 CFR 280.45.
[February 7, 1995 letter to Mr. Staab (PDF) (2 pp, 11K)]
Question 14: Do I have to report a suspected release if
my inventory control results from two consecutive months both exceed the
performance standard, but one is short and the other is over? Does
this "confirm the initial result"?
[Sept. 18, 1995 letter from Robert Stabb, Circle K Stores Inc.]
Answer: Yes, reporting is required. EPA interprets
"confirm the initial result" at 280.50(c)(2) to mean a second exceedance,
no matter whether the direction -- short or over -- is the same as the
[December 12, 1995 letter to Mr. Stabb (PDF) (5 pp, 21K)]
Question 15: When can I use the combination of tightness testing every 5 years and inventory control for leak detection on my upgraded UST?
Answer: Owners/operators may begin using the combination
of inventory control and 5-year tightness tests only after the entire UST
system meets 1998 standards. This means that the UST system must have corrosion
protection for both tank and piping, spill, and overfill protection. The
combination of inventory control and tank tightness testing may be used
until 10 years after the tank itself has met corrosion protection requirements
or until 12/22/98, whichever is later. After this time, another monthly
method for release detection must be used.
[July 25, 1997 memorandum to State and Regional Program Managers (PDF) (4 pp, 23K)]