Overview
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

Leak Detection for Underground Suction Piping

Will I be in compliance?

When installed and operated according to manufacturer's specifications, the leak detection methods discussed here meet the Federal regulatory requirements for the life of new and existing underground suction piping systems. You should find out if state or local requirements allow all these methods or have other requirements that are different from those described below.

How do the methods work?

Line Tightness Testing

Tightness tests must be conducted at least every three years. The line is taken out of service, pressurized (typically less than 15 psig) and allowed to stabilize. A drop in pressure over time, preferably one hour, suggests a possible leak.

In the event of trapped vapor pockets, it may not be possible to conduct a valid line tightness test. There is no way to tell definitely before the test begins if this will be a problem, but longer complicated piping runs with a lot of risers and dead ends are more likely to have vapor pockets.

Most line tightness tests are performed by a testing company. You just observe the test. Some tank tightness test methods can be performed to include a tightness test of the connected piping. For most line tightness tests, no permanent equipment is installed.

Groundwater or Vapor Monitoring

Groundwater monitoring checks for leaked product floating on the groundwater near the piping. Vapor monitoring detects product that leaks into the soil and evaporates there.

A monitoring well should be installed every 20 to 40 feet. UST systems using groundwater or vapor monitoring for the tanks are well suited to use the same monitoring method for the piping.

See the earlier sections on groundwater and vapor monitoring. Use of these methods with piping is similar to that for tanks.

Secondary Containment with Interstitial Monitoring

A barrier is placed between the piping and the environment. Barriers such as double-walled piping or a leakproof liner in the piping trench can be used.

A monitor is placed between the piping and the barrier to sense a leak if it occurs. Monitors range from a simple stick that can be put in a sump to see if a liquid is present, to continuous automated systems, such as those that monitor for the presence of evaporated product. Proper installation of secondary containment is the most important and the most difficult aspect of this leak detection method. Trained and experienced installers are necessary.

See the section on secondary containment for additional information. Secondary containment for piping is similar to that for tanks.

What are the regulatory requirements?

No leak detection is required if the suction piping has: (1) enough slope so that the product in the pipe can drain back into the tank when suction is released; and (2) has only one check valve, which is as close as possible beneath the pump in the dispensing unit. If a suction line is to be considered exempt based on these design elements, there must be some way to check that the line was actually installed according to these plans.

If a suction line does not meet all of these design criteria, one of the following leak detection methods must be used:

The line tightness test must be able to detect a leak at least as small as 0.1 gallon per hour. By December 1990, the test must also meet the Federal regulatory requirements regarding probabilities of detection and false alarm.

Groundwater, vapor, and interstitial monitoring hate the same regulatory requirements for piping as they do for tanks. See the earlier sections on those methods.

What other information do I need?

Purchasing piping leak detection is Similar to any other major purchase. You should "shop around," ask questions, get recommendations, and select a method and company with experience and one that can meet the needs of your site.

How much does it cost?

Line Tightness Testing

When performed at the same time as a tank tightness test, a typical line test costs about $50-100. The price varies with the length and complexity of the piping.

If a testing company comes on-site to perform only a line tightness test, the cost will probably be much higher unless you can negotiate for a package deal for a larger number of tests. Not all tightness testing companies will do independent line tests.

Secondary Containment with Interstitial Monitoring

The total installed cost for double-walled piping for a typical 3-tank station is $10,000, not including digging the trenches. Costs vary with size of pipe, length of run, site conditions, and contractor. In general, double-walled piping systems cost about 3 times as much as single-walled systems.

For a typical station, trench liners cost about $25 to $40 per linear foot for 2-inch pipes, depending on the number of pipes. Installation is about $800 to $1,500, depending on site conditions.

The costs of a monitor range from essentially nothing for a dipstick to a total installed cost of about $1,000 for an electronic sensor (not including control panel).