Issue Date:  September 7, 2005
Revision Date: July 13, 2007

Praxair Services, Inc.

Tracer Tight For Large Aboveground Storage Tank Systems



Leak rate of 0.1 gph with PD = 100% and PFA = 0%. 
Leak rate of 0.005 gph with PD = 97% and PFA = 2.9%.
The US EPA has not set a minimum detectable leak rate for aboveground storage tank systems at the time of this evaluation.

Leak Threshold

A tank system should not be declared tight when tracer chemical greater than the background level is detected outside of the tank system.


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

Tank Capacity

Not limited by capacity.

Waiting Time

Ranges from 7 to 30 days after tracer is added to tank without support of on-site leak simulation.
The waiting period may be adjusted below this range when supported by on-site leak simulations performed as described below.

Leak Simulations

The release of surrogate tracer into the soil beneath the tank 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 simulations location in order to use the results. This requirement may be satisfied by sampling the soil beneath the tank, and/or making flow/vacuum measurements from the sampling probes.

Tracer Dosage

Dosage of tracer is based on tank size, product volume in tank, and frequency and volume of tank refills according to manufacturer's recommendations.


Soil permeability must readily allow tracer movement (greater than 1 Darcy).
The permeability of the soil beneath the tank must be verified by the detection of a leak simulation tracer in a sample collected at least 13 feet from the release location.


Typical probe radius during evaluation was 10 to 12 feet. 
All tank surfaces must be within the zone of influence of a sampling probe. 
Probes must be installed per manufacturer's guidelines.
Probe radius below an AST can be increased beyond the 10 foot limit when supported by a leak simulation as described above.


Depth to groundwater must be at least 2 inches below bottom of tank.
Groundwater less than 2 inches below bottom of tank may limit effectiveness of test method.


Tester may determine that pre or post testing is needed to establish the background level of tracer in the soil.
The presence of a layer of water saturated soil, or frozen soil, may inhibit the effectiveness of the method by impeding the transport of the tracer labeled product into the unsaturated zone.
The system should be installed and operated in accordance with Praxair Services, Inc.’s “AST Testing Procedures” document.


Praxair Services, Inc.

Evaluator:  Ken Wilcox Associates

3755 N. Business Center Dr.

Tel:  (816) 443-2494

Tucson, AZ 85705

Date of Evaluation:  10/04/90

Tel:  (800) 394-9929

Evaluator: Control Strategies Engineering (out of business)
E-mail: Tel: Contact Praxair Services, Inc.


Date of Evaluation:  05/92


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