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 Pressurized Underground Piping

Will I be in compliance?

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

New pressurized piping must have leak detection when it is installed. Existing pressurized piping must meet the leak detection regulatory requirements by December 22,1990.

How do the methods work?

Automatic Line Leak Detectors (LLD)

Flow restrictors and flow shutoffs can monitor the pressure within the line in a variety of ways: whether the pressure decreases over time; how long it takes for a line to reach operating pressure; and combinations of increases and decreases in pressure.

A flow restrictor keeps the product flow through the line well below the usual flow rate, and if a possible leak is detected, a flow shutoff completely cuts off product flow in the line or shuts down the pump.

A continuous alarm system constantly monitors line conditions and immediately triggers an audible or visual alarm if a leak is suspected. Automated vapor or interstitial line monitoring systems can also be set up to operate continuously and sound an alarm, flash a signal on the console, or even ring a telephone in a manager's office when a leak is detected.

Both automatic flow restrictors and shutoffs are permanently installed directly into the pipe or the pump housing. Vapor and interstitial monitoring systems can be combined with automatic shutoff systems so that whenever the monitor detects a possible release the piping system is shut down. This would qualify as a continuous alarm system. Such a setup would meet the monthly monitoring requirement as well as the LLD requirement.

Line Tightness Testing

The line is taken out of service and pressurized, usually above the normal operating pressure. It should be allowed to stabilize, ideally for several hours, before the test. 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.

Tightness tests must be conducted annually. 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.

Tracer methods do not measure pressure or flow rates of the product. Instead they use a tracer chemical to determine if there is a hole in the line. With tracer methods, all of the factors above may not apply.

Secondary Containment with Interstitial Monitoring

Proper installation of secondary containment is the most important and the most difficult aspect of this release 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.

Groundwater or Vapor Monitoring

Groundwater monitoring checks for leaked product floating on the ground water 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 for additional information. Use of these methods with piping is similar to that for tanks.

What are the regulatory requirements?

Each pressurized piping ran must have one Automatic Line Leak Detector:

And one other method:

The automatic line leak detector (LLD) must be able to detect a leak at least as small as 3 gallons per hour at a line pressure of 10 psi(g) within 1 hour by shutting off the product flow, restricting the product flow, or triggering an audible or visual alarm.

The line tightness test must be able to detect a leak at least as small as 0.1 gallon per hour when the line pressure is one and one-half times its normal operating pressure.

By December 1990, automatic LLDs and line tightness tests must also be able to meet the Federal regulatory requirements regarding probabilities of detection and false alarm.

Groundwater, vapor, and interstitial monitoring have 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 release detection is similar to any other major purchase. You should "shop around," ask questions, get recommendations, and select a method and company that can meet the needs of your UST site.

How much does it cost?

Automatic Line Leak Detectors (LLD)

Automatic flow restrictors: total installed cost about $300-$400 per line.
Automatic shutoff devices: total installed cost for one line is about $2,000. There may be cost savings for multiple lines or when you include tank monitoring in the same system.
The annual operating costs are negligible.

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 a package deal for a large 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 at a typical 3-tank station is about $10,000, not including digging the trenches. Costs vary with the 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.

Costs for interstitial monitoring devices range from essentially nothing for a dipstick to a total installed cost of about $1,000 per line for an electronic sensor (not including the control panel).

Groundwater or Vapor Monitoring

If you have already selected groundwater or vapor monitoring for your tanks, the additional cost to include the piping in the monitoring network may be relatively small if only wells need to be added. If an underground cable or an extra control panel is needed for an automated system, the costs will be higher. See the sections on groundwater and vapor monitoring for costs of tank monitoring. See the sections on groundwater and vapor monitoring for costs of tank monitoring.