Underground Storage Tank Leak Detection Requirements

The greatest potential threat from a leaking underground storage tank (UST) is contamination of groundwater, the source of drinking water for nearly half of all Americans. Effective leak detection systems can help protect you from the high costs of cleaning up extensive leaks and responding to third-party liability claims.

All underground storage tanks installed after December 1988 are required to contain leak detection mechanisms. Those installed before December 1988 had to meet leak detection compliance deadlines that were phased in over a five-year period, and by December 1993, all of these USTs had to have leak detection.
The Environmental Protection Agency (EPA) has identified the following seven methods that owners and operators may use to meet the federal leak detection requirements:

1. 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 toward an interstitial monitor located between the inner tank or piping and the outer barrier. There are a number of interstitial monitoring methods including the use of a simple dipstick or a continuous, automated vapor or liquid sensor permanently installed in the system to monitor interstitial spaces. Interstitial spaces can also be filled with brine or glycol solutions and their levels monitored. Also, sophisticated pressure/vacuum monitoring systems may be used to indicate pressure changes within these spaces.
2. 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.
3. Vapor Monitoring (including tracer compound analysis)
   Vapor monitoring checks for leaks by measuring the soil around the UST for escaping product fumes or special tracer chemicals. 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.
4. 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.
5. Statistical Inventory Reconciliation
   In this method, a trained professional uses sophisticated computer software to analyze inventory, delivery and dispensing data, which the owner must supply regularly. Also, the owner can purchase software and enter data into his or her own computer, which statistically analyzes the information.
6. Tank Tightness Testing with Inventory Control
   This method combines periodic tank tightness testing with monthly inventory control. Inventory control involves taking measurements of tank contents and recording amount pumped each operating day, as well as reconciling all this data at least once a month. This combined method must also include tightness tests, which are performed by trained professionals. This combined method can be used only temporarily (usually for 10 years or less).
7. 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 five 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.

Third Party Evaluations

Make sure the vendor of the leak detection method you use has provided you with evidence that your leak detection meets regulatory requirements for performance. An evaluation performed by a third party (someone who is independent of the manufacturer or vendor of the leak detection system) shows that a leak detection system can work as designed. The evaluation follows required evaluation procedures and often takes place in a laboratory. The EPA and various third parties have developed evaluation procedures for all leak detection systems.

Although an evaluation and its resulting documentation are technical, you should be familiar with the evaluation’s report and its results form. You should obtain this documentation from the leak detection vendor and keep it on file. The report also contains a signed certification that the system performed as described, as well as documenting any limitations of the system. This information is important to your compliance with the UST requirements. For example, if a tank tightness test was evaluated and certified only for tests taking two hours or more, then your UST must be tested for at least two hours or it would fail to meet the leak detection requirements.

Required Probabilities for Some Leak Detection

The regulations require not only that leak detection methods be able to detect certain leak rates, but that they also give the correct answer consistently. In general, methods must detect the specified leak rate with a probability of detection of at least 95 percent and a probability of false alarm of no more than five percent. Simply stated, of 100 tests of USTs leaking at the specified rate, at least 95 of them must be correctly detected. It also means that, of 100 tests of non-leaking USTs, no more than five can be incorrectly called leaking.

Which Leak Detection Method is Best for You?

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 leak detection method has unique characteristics. For example, vapor detection devices work rapidly and most effectively in porous soils, while liquid detectors are only appropriate for areas with a high water table.

Identifying the best leak detection choice for your UST depends on a number of factors including cost (both initial installation cost and long-term operation and maintenance cost), facility configuration (such as complexity of piping runs and manifold tanks), groundwater depth, soil type, seasonal rainfall and temperature ranges, availability of experienced installers and other variables.

It is wise to research extensively for experienced, professional vendors and installers of leak detection. Ask questions that help you find the most reliable, cost-effective leak detection for your type of facility. Some possible information sources are: references from fellow UST owners, oil marketers, equipment suppliers, trade journals, trade associations, state and local trade associations (especially those for petroleum marketers and UST owners) and state and local regulatory authorities. Your state may also have an assistance fund that may be able to help you pay for your UST’s leak detection.

National Work Group on Leak Detection Evaluations (NWGLDE) also maintains a list of leak detection equipment whose third-party conducted documentation has been reviewed by the organization. The list contains a detailed summary of specifications for over 325 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. The list can be accessed at http://www.nwglde.org.

For additional information about federal UST requirements, visit the EPA’s website at www.epa.gov/oust.