Certification

Leak rate of 0.005 gph, or greater**, with PD = 97.6% and PFA = 0%.

Leak Threshold

A tank should not be declared tight when the chemical marker detected exceeds the background level outside of the tank.

Applicability

Gasoline, diesel, aviation fuel, fuel oil #4, fuel oil #6, solvents, waste oil, other gases (LP, Natural, Toxic), ethanol blends up through E100, biodiesel blends B6-B20 meeting ASTM D7647, biodiesel B100 meeting ASTM D6751*.

Tank Capacity

Not limited by capacity.

Waiting Time

A range from 5 to 31 days after the chemical marker is mixed throughout the tank to be tested.
The waiting period may be adjusted below or above this range when supported by “Controlled Leak Points” as described below.
The waiting time or test period begins once the chemical marker has been mixed and distributed throughout the tank system(s) to be tested.

Controlled Leak Points

"Controlled Leak Point” is a port where chemical marker is injected directly into the soil surrounding the tank to confirm the adjusted leak rate and the rate at which the chemical marker migrates through the backfill. It can be used to demonstrate that the metered amount of chemical marker will migrate through the soil to a detection point in a documented amount of time, as described in manufacturer’s procedures. When installing sampling ports in soil conditions that are uniquely different from standard engineered backfill a controlled leak point shall be used

Chemical Marker Dosage

Dosage of the chemical marker, either liquid, vapor or both is based on tank volume and the duration of time the inoculated product will remain within the tank.
Tanks are typically tested in an in-service operating condition; tanks that are out of service are tested at working pressure. Chemical marker concentration and sampling points are adjusted to meet the test specifications.

Soil Permeability

Soil permeability must readily allow chemical marker movement through the excavation backfill (greater than 1 Darcy) or the use of a controlled leak point is required.

Groundwater

Depth to groundwater must be determined.
When the regulatory agency allows testing to be performed with high groundwater below the bottom of tanks containing water based or water soluble products, the product must be removed from the tank prior to testing and tested with a non-water soluble product or a vapor chemical marker.

Comments

This method can be used to test single-walled and double-walled tanks for leakage to soil by sampling in the backfill or to test the primary containment integrity of a double-wall tank by sampling in the interstitial space.
Evaluator indicates that the detectable leak rate can be adjusted by controlling test variables such as chemical marker concentration and test duration.
The tester may determine that pre or post testing is needed to establish the background level of chemical marker in the soil.
For shorter/longer test periods, for different sampling port spacing, or in soil conditions that are uniquely different from standard engineered backfill, such as water saturated frozen soil, a controlled leak point shall be installed to document the chemical marker migration period.

*NWGLDE Listings apply to leak detection functionality only and not material compatibility – see “Disclaimer”.
**See manufacturer instructions for detail