• Leak testing, or “tank tightness testing,” must be performed regularly on buried metallic storage tanks.

Completely buried metallic storage tanks installed on or after January 10, 1974, must be regularly leak tested. “Regular testing” means testing in accordance with industry standards or at a frequency sufficient to prevent leaks. Appropriate methods of testing should be selected based on good engineering practice, and tests conducted in accordance with Part 280.43 or a state program approved under Part 281 are acceptable.

Leak testing is often referred to as “tank tightness testing.” Tank tightness tests include a wide variety of methods. Other terms used for these methods include precision, volumetric, and nonvolumetric testing. The features of tank tightness testing vary by method, as described in the Environmental Protection Agency (EPA) Guidance^[1] on meeting UST system requirements:

• Many tightness test methods are volumetric methods in which the change in product level in a tank over several hours is measured very precisely (in milliliters or thousandths of an inch).
• Other methods use acoustics or tracer chemicals to determine the presence of a hole in the tank. With such methods, all of the factors in the following bullets may not apply.
• For most methods, changes in product temperature also must be measured very precisely (thousandths of a degree) at the same time as level measurements, because temperature changes cause volume changes that interfere with finding a leak.
• For most methods, a net decrease in product volume (subtracting out volume changes caused by temperature) over the time of the test indicates a leak.
• The testing equipment is temporarily installed in the tank, usually through the fill pipe.
• The tank must be taken out of service for the test, generally for several hours, depending on the method.
• Many test methods require that the product in the tank be a certain level before testing, which often requires adding product from another tank onsite or purchasing additional product.
• Some tightness test methods require all of the measurements and calculations to be made by hand by the tester.
• Other tightness test methods are highly automated. After the tester sets up the equipment, a computer controls the measurements and analysis.
• A few methods measure properties of the product that are independent of temperature, such as the mass of the product, and so do not need to measure product temperature.
• Some automatic tank gauging systems are capable of meeting the regulatory requirements for tank tightness testing and can be considered as an equivalent method.

The Spill Prevention, Control, and Countermeasure (SPCC) Plan must describe the method and schedule for testing completely buried tanks.

^{[1] For more information on tank tightness testing, see http://www.epa.gov/oust/ustsystm/inventor.htm. For more information on preventing and detecting underground storage tank system leaks, see http://www.epa.gov/oust/prevleak.htm.}