Issue Date: October 13, 2006
Revision Date: July 13, 2007

Praxair Services, Inc.


Line Leak Detection Method for Airport Hydrant and Field Constructed Systems


Leak rate of 0.1 gph with PD = >99% and PFA = <1%.
The US EPA has not set a minimum detectable leak rate for large diameter pipeline systems (airport hydrant systems) at the time of this evaluation.

Leak Threshold

A pipeline system should not be declared tight when a confirmable level of chemical tracer in the sample collected exceeds the background level.


Gasoline, diesel, aviation fuel, fuel oil #4, waste oil. 

Pipeline Capacity

Not limited by capacity.
Pipeline segments up to 1500 feet in length may be covered by an individual test sample collected continuously along this length.

Waiting Time

Ranges from 1 to 6 days after tracer is added to the product in the pipeline. 
All releases at a depth of 5 feet in non-engineered backfill were detected within 1 day after the start of the test.  All releases at a depth of 10 feet were detectable 6 days after the start of the test.
Leak simulations conducted at the depth of the pipeline can be used to validate test parameters such as soil permeability and waiting period.
For very large pipeline systems, several days or weeks may be required to circulate tracer-labeled product through all parts of the pipeline.
Waiting time begins after the tracer has reached the portions of the pipeline being tested.

Leak Simulations

Leak simulations are the release of surrogate tracer into the soil or backfill at the depth of the pipeline to evaluate the migration of a tracer and the sensitivity of the test under on-site sub-surface conditions. Sub-surface conditions throughout the test area must be at least as favorable as those at the leak simulation location in order to use the results.

Tracer Dosage

Dosage of tracer is based on pipe capacity and frequency and volume of pipe use according to manufacturer's recommendations. 
Tracer-labeled product must be circulated through the pipeline before test period begins. 
Pressurized pipeline must be brought up to operating pressure or operated on a daily basis.

System Features

Pipeline must be accurately located to ensure that sampling activity is within the zone of influence of the tracer. 
Sampling is conducted using a small metal sled that is pulled on the ground above the pipeline being tested.


The tester may determine that pre or post testing is needed to establish the background level of tracer in the soil.
Due to the vapors being collected at the surface, testing can be affected by extreme windy conditions.
High winds will generally cause a reduction in the amount of tracer from a release that is collected in the test sample.
The presence of a layer of water saturated soil, that is also frozen, above the location where a leak may exist, may impede the transport of the tracer labeled product into the sampling zone.
Groundwater surrounding the pipeline may limit effectiveness of test method (e.g. when applied to pipelines containing water-miscible products or products whose specific gravity is greater than 1).
Leak simulations performed at the depth of the pipeline along sections of the pipeline below the water table or below saturated, frozen soil allow for validation of the method in these conditions.


Praxair Services, Inc.

Evaluator:  Ken Wilcox Associates

3755 N. Business Center Dr.

Tel:  (816) 443-2494

Tucson, AZ 85705

Date of Evaluation:  12/20/02

Tel:  (800) 394-9929





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