Issue Date: April 18, 1997
Revision Date: August 23, 1999

Universal Sensors and Devices, Inc.

LTC-1000 (Mass Buoyancy Probe)

Bulk Underground Storage Tank Leak Detection Method (50,000 Gallons or Greater)

Certification

Leak rate is proportional to product surface area (PSA).
For tanks with PSA of 14,244 ft², leak rate is 1.4 gph with PD = 97.2% and PFA = 2.8%.
For other tank sizes, leak rate equals [(PSA in ft² ÷ 14,244 ft²) x 1.4 gph].

Example:
For a tank with PSA = 20,000 ft²; leak rate = [(20,000 ft² ÷ 14,244 ft²) x 1.4 gph] = 2.0 gph.
Calculated minimum detectable leak rate is 1.18 gph with PD = 95% and PFA = 5%.
Leak rate may not be scaled below 0.2 gph.
Leak Threshold

Leak threshold is proportional to product surface area (PSA).
For tanks with PSA of 14,244 ft², leak threshold is 0.7 gph.
For other tank sizes, leak threshold equals [(PSA in ft² ÷ 14,244 ft²) x 0.7 gph].

Example:
For a tank with PSA = 20,000 ft²; leak threshold = [(20,000 ft² ÷ 14,244 ft²) x 0.7 gph] = 1.0 gph.
A tank system should not be declared tight if the test result indicates a loss or gain that equals or exceeds the calculated leak threshold.
Applicability Gasoline, diesel, aviation fuel, fuel oil #4.
Other liquids may be tested after consultation with the manufacturer.
Tank Capacity Use limited to single field-constructed vertical tanks larger than 50,000 gallons.
Maximum product surface area (PSA) is 35,610 ft² (approximately 213 ft. diameter).
Performance not sensitive to product level.
Waiting Time Minimum of 3 hours, 42 minutes after delivery.
Valve leaks and pump drain-back may mask a leak.
Allow sufficient waiting time to minimize these effects.
None between dispensing and testing.
Test Period Minimum of 49 hours.
There must be no dispensing or delivery during test.
Temperature Measurement not required by this system.
Water Sensor None.
Water leaks are measured as increase in mass inside tank.
Calibration Probe must be checked and, if necessary, calibrated in accordance with manufacturer's instructions.
Comments Tests only portion of tank containing product.
As product level is lowered, leak rate in a leaking tank decreases (due to lower head pressure).
Consistent testing at low levels could allow a leak to remain undetected.
Evaluated in a nominal 2,000,000 gallon, vertical underground tank with product surface area (PSA) of 14,244 ft².
  • Universal Sensors and Devices, Inc.
    9205 Alabama Ave., Unit C
    Chatsworth, CA 91311
    Tel: (800) 899-7121, (818) 998-7121
  • Evaluator: Ken Wilcox Associates
    Tel: (816) 443-2494
    Date of Evaluation: 05/17/96

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