Ground water monitoring
Vapor monitoring
Secondary containment with interstitial monitoring
Automatic tank gauging systems
Tank tightness testing and inventory control
Manual tank gauging
Leak detection for underground suction piping
Leak detection for pressurized underground piping
Statistical inventory reconciliation
More information

As An Owner Or Operator Of Underground Storage Tanks...

These are important questions, because your USTs must have leak detection NOW. These web pages contain information you can use to answer questions about UST leak detection requirements and methods.

These web pages begin with an overview of the federal regulatory requirements for leak detection. Following sections focus on leak detection methods and the special requirements for piping.


Federal UST regulations require all UST systems to have leak detection. This section explains when you need leak detection and what your basic leak detection choices are.

With effective leak detection, you can respond quickly to signs of leaks. You can minimize the extent of environmental damage and the threat to human health and safety. Early action on your part also protects you from the high costs that can result from cleaning up extensive leaks and responding to third-party liability claims.

NOTE: Much of the information on these pages is excerpted from the EPA booklet, Straight Talk on Tanks, available in PDF and other formats.

When is Leak Detection Necessary?

All new USTs (those installed after December 1988) must have leak detection when they are installed. USTs installed before December 1988 (called "existing USTs") had compliance deadlines for leak detection phased in over 5 years. As of December 1993, all existing USTs must have leak detection. State and local regulations may be more stringent than Federal requirements, so you should always check to see which requirements you need to meet.

What Leak Detection Methods Are OK?

You need to remember that State or local regulations may differ from the Federal requirements, so be sure to check and see which requirements apply to your UST. Rather than requiring specific technologies, the Environmental Protection Agency has identified a variety of general leak detection methods that owners and operators can use to meet the Federal requirements. You can use:

These are all monthly monitoring methods and eventually everyone must use at least one of them. However, as a temporary method (for 10 years after new tank installation and for up to 10 years for existing tanks), you can combine tank tightness testing and manual monthly inventory control (or manual tank gauging if you have a very small tank).

Not all of these leak detection methods can be used for both tanks and piping. Leak detection methods for piping include groundwater monitoring, vapor monitoring, secondary containment with interstitial monitoring, and tightness testing. Pressurized piping must also have an automatic line leak detector. See later sections on suction and pressurized piping for full discussions of the requirements for piping.

Brief descriptions of leak detection methods follow, with more detail given on the other pages in this section.

Groundwater Monitoring

Groundwater monitoring senses the presence of liquid product floating on the groundwater. This method requires installation of monitoring wells at strategic locations in the ground near the tank and along the piping runs. To discover if leaked product has reached groundwater, these wells can be checked periodically by hand or continuously with permanently installed equipment. This method cannot be used at sites where groundwater is more than 20 feet below the surface.

Vapor Monitoring

Vapor monitoring measures product "fumes" in the soil around the UST to check for a leak. This method requires installation of carefully placed monitoring wells. Vapor monitoring can be performed manually on a periodic basis or continuously using permanently installed equipment.

Secondary Containment With Interstitial Monitoring

Secondary containment often uses a barrier, an outer wall, a vault, or a liner around the UST or piping. Tanks can be equipped with inner bladders that provide secondary containment. Leaked product from the inner tank or piping is directed towards an "interstitial" monitor located between the inner tank or piping and the outer barrier. Interstitial monitoring methods range from a simple dipstick to a continuous, automated vapor or liquid sensor permanently installed in the system.

Automatic Tank Gauging Systems

A probe permanently installed in the tank is wired to a monitor to provide information on product level and temperature. These systems automatically calculate the changes in product volume that can indicate a leaking tank.

Statistical Inventory Reconciliation

In this method, a trained professional uses sophisticated computer software to conduct a statistical analysis of inventory, delivery, and dispensing data, which you must supply regularly.

Other Methods Meeting Performance Standards

Any technology can be used if it meets a performance standard of detecting a leak of 0.2 gallons per hour with a probability of detection of at least 95 percent and a probability of false alarm of no more than 5 percent. Regulatory authorities can approve another method if you demonstrate that it works as well as one of the methods above and you comply with any condition the authority imposes.

Tank Tightness Testing and Inventory Control

Tightness tests require temporarily installing equipment in the tank. There are two types of tightness tests: volumetric and non-volumetric. A volumetric test involves filling the tank to a specified level and precisely measuring the change in level and temperature over several hours. Non-volumetric test methods include ultrasound techniques and tracer gas detectors. These are sophisticated tests and must be performed by trained, experienced professionals.

In addition to tightness testing, you must use monthly inventory control. Inventory control is like balancing a checking account. Every month the product volume is balanced between what is delivered and sold from the tank (this is what the "bank" says you have) with daily measurements of tank volume taken with a gauge stick (these measurements indicate what you actually have). If your "account' doesn't balance, you may have a leak.

Remember, this combined method can be used only during the first 10 years following new tank installation or upgrade of your existing UST. After that, you must use monthly monitoring methods.

Manual Tank Gauging

Manual tank gauging can be used only for tanks of 2,000 gallons or less capacity. This method requires keeping the tank undisturbed for at least 36 hours each week, during which the contents of the tank are measured twice at the beginning and twice at the end of the test period. At the end of each week you compare the results to the standards shown on page 21 to see if your tank may be leaking. This method can be used by itself only for tanks up to 1,000 gallons. Tanks between 1,001 and 2,000 gallons can use this method only in combination with periodic tank tightness testing. This combined method can be used only temporarily (usually for 10 years or less).

Which Method Is Best For You?

Choosing leak detection is not a cut-and-dried process. There is no one leak detection system that is best for all sites, nor is there a particular type of leak detection that is consistently the least expensive.

Each of the leak detection methods has advantages and disadvantages. For example, vapor detection devices work rapidly and most effectively in dry soils, while liquid detectors are most appropriate for areas with a high water table. Identifying the correct option or combination of options depends on a number of factors including cost, tank type, groundwater depth, soil type, and other variables.

The various factors that influence the selection and use of leak detection options are discussed in the Federal regulations and in the following sections.

You will want to find the best fit between what you need and what is available. The following table lists a few of the factors that could influence your selection of the leak detection method that is best for your site.

The free publication, List Of Leak Detection Evaluations For UST Systems, maintained by the EPA and state agency representatives, contains a detailed summary of specifications, based on third-party evaluations, for over 250 leak detection systems. Although the List can be used to help select systems and determine their compliance or acceptability, the publication is not a list of "approved" leak detection systems. Approval or acceptance of leak detection systems rests with the implementing agency, in most cases the state environmental agency.

Detection Options

Site-specific Factors

Tank-related Factors

Cost Factors

Ground Water Monitoring Do not use if ground water level is greater than 20 feet, if clay soil is present, or if existing product is already on the ground water. Product must be able to float on water and not mix easily with water. Well Installation: $15 - $70/ ft depth.
Equipment: $200 - $5000 per tank.
Vapor Monitoring Do not use at sites where soil is saturated with water, the backfill is clay, or soil vapor levels are too high. Product must evaporate easily or substance that evaporates easily must be added to the tank. $1200 - $6000 per tank for equipment and installation.
Secondary Containment with Interstitial Monitoring Site conditions (such as too much water) may require use of containment that completely surrounds tank or piping. A double walled system must be able to detect a release through the inner wall. Total installed cost of $5000 - $12,000 per tank.
Automatic Tank Gauging System (ATGS) If water collects in excavation, ATGS must have a water sensor. To date, used primarily at sites with gasoline and diesel tanks under 15,000 gallons. Per tank:
Equipment = $2300 - $3900
Installation = $500 - $3000.
Tank Tightness Testing Volumetric methods must account for presence of ground water and product temperature. To date, used primarily at sites with gasoline and diesel tanks under 15,000 gallons. $250 - $1000 per test tank for problem- free test. If problems occur, cost may be much higher.
Inventory Control None None Under $200, but may also require tightness testing.
Manual Tank Gauging None Limited to tanks under 1001 gallons when used alone or under 2000 gallons when combined with tightness testing. Under $200, but may also require tightness testing.
Automatic Line Leak Detectors None Used only for pressurized lines. Total installed cost of $400 - $2000 per line.
Line Testing Tightness None Used only for piping. $50 - $100 per test per line if conducted with tank test. May be more expensive if conducted alone. Must do test every 3 years.