Tank Tightness Testing with Inventory Control
When performed according to the manufacturer's specifications, periodic tank tightness testing combined with monthly inventory control can temporarily meet the federal release detection requirements for tanks (this method does not detect piping leaks). Inventory control alone does not meet the federal requirements for release detection for tanks.
Tightness testing (if conducted at least every 3 years) is also an option for underground piping.
Tank Tightness Testing
How does tank tightness testing work?
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 are:
- 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 on-site 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. Check with your implementing agency.
What are the regulatory requirements for tank tightness testing?
- The tightness test method must be able to detect a leak at least as small as 0.1 gallon per hour with certain probabilities of detection and of false alarm.
- Tightness tests must be performed periodically. UST systems installed on or before [180 days after effective date] must have tank tightness tests every 5 years for 10 years following installation.
- After the applicable time period noted above, you must have a monitoring method that can be performed at least once every 30 days.
- Beginning on [three years after effective date], you must test your release detection equipment annually to make sure it is working properly:
- Tank tightness testing is typically performed by a qualified testing company. Therefore, this requirement may not be applicable. If your implementing agency allows use of ATG systems for tank tightness testing, you must follow the testing procedures required for ATG systems.
Anything else about tank tightness testing that you should consider?
- For most methods, the test is performed by a testing company. You just observe the test.
- Tank tightness testing has been used primarily on tanks no more than 15,000 gallons in capacity containing gasoline and diesel. If you are considering using tightness testing for larger tanks or products other than gasoline or diesel, discuss the method's applicability with the manufacturer's representative.
- Manifolded tanks generally should be disconnected and tested separately.
- Procedure and personnel, not equipment, are usually the most important factors in a successful tightness test. Therefore, well-trained and experienced testers are very important. Some states and local authorities have tester certification programs.
How does inventory control work?
Inventory control requires daily measurements of tank contents and mathematical calculations that let you compare your stick inventory (what you've measured) to your book inventory (what your recordkeeping indicates you should have. If the difference between your stick and book inventory is too large, your tank may be leaking.
EPA's booklet, Doing Inventory Control Right, explains how to do inventory control with simple step-by-step directions. The booklet also includes standard forms used to record inventory data.The features of inventory control are:
- UST inventories are determined daily by using a gauge stick and the data is recorded on a form. The level on the gauge stick is converted to a volume of product in the tank using a calibration chart, which is often furnished by the UST manufacturer.
- The amounts of product delivered to and withdrawn from the UST each day are also recorded. At least once every 30 days, the gauge stick data and the sales and delivery data are reconciled and the month's overage or shortage is determined. If the overage or shortage is greater than or equal to 1.0 percent of the tank's flow-through volume plus 130 gallons of product, the UST may be leaking.
What are the regulatory requirements for inventory control?
- Inventory control must be used in conjunction with periodic tank tightness tests.
- The gauge stick should be long enough to reach the bottom of the tank and marked so that the product level can be determined to the nearest one-eighth of an inch. A monthly measurement must be taken to identify any water at the bottom of the tank.
- Product dispensers must be calibrated to the local weights and measures standards.
- Beginning on [three years after effective date], you must perform the following, as applicable, on your release detection equipment annually to make sure it is working properly:
For hand held non-electronic equipment (such as tank gauge sticks):
- Check for operability and serviceability
- Keep records of these checks for one year
Anything else about inventory control that you should consider?
- Inventory control is a practical, commonly used management tool that does not require closing down the tank operation for long periods.
- The accuracy of tank gauging can be greatly increased by spreading product-finding paste on the gauge stick before taking measurements (or by using in-tank product level monitoring devices).
- If your tank is not level, inventory control may need to be modified. You will need to get a corrected tank chart.
Time restrictions on the use of this combined method...
USTs installed on or before [180 days after effective date] may use this method for 10 years after the date the tank was installed or upgraded with corrosion protection. Note that the end date is based on the compliance status of the tank only, not the entire UST system. As a result, some USTs may not be able to use this combined method for as long as 10 years. At the end of the valid period, you must use one of the monthly monitoring release detection choices described herein.
USTs installed or replaced after [180 days after effective date] may no longer use inventory control combined with periodic tank tightness testing as the primary method of release detection. USTs must be secondarily contained and use interstitial monitoring.