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Issue Date: August 23, 1999
Vista Precision Solutions, Inc.
(originally listed as Vista Research, Inc. and Naval Facilities Engineering Service Center)
LRDP-24 (V1.1)
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 6,082 ft², leak rate is 0.856 gph with PD = 95% and
PFA = 0.017%.
For other tank sizes, leak rate equals [(PSA in ft² ÷ 6,082 ft²) x 0.856
gph].
Example:
For a tank with PSA = 10,000 ft²; leak rate = [(10,000 ft² ÷ 6,082 ft²) x
0.856 gph] = 1.407 gph. Calculated minimum detectable leak rate is 0.446 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 6,082 ft², leak threshold is 0.632 gph.
For other tank sizes, leak threshold equals [(PSA in ft² ÷ 6,082 ft²) x
0.632 gph].
Example:
For a tank with PSA = 10,000 ft²; leak threshold = [(10,000 ft² ÷ 6,082 ft²)
x 0.632 gph] = 1.039 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.
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| Applicability |
Gasoline, diesel,
aviation fuel.
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| Tank Capacity |
Use limited to
single field-constructed vertical tanks larger than 50,000 gallons.
Maximum product surface area (PSA) is 15,205 ft² (approximately 139 ft
diameter).
Performance not sensitive to product level. |
| Waiting Time |
Minimum of 24
hours after delivery or dispensing.
Valve leaks and pump drain-back may mask a leak.
Allow sufficient waiting time to minimize these effects.
Waiting times during evaluation ranged from 16.08 to 115.8 hours.
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| Test Period |
Minimum of 24
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.
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| Calibration |
Differential
pressure sensor must be checked regularly 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 600,000 gallon, vertical underground tank with
product surface area (PSA) of 6,082 ft².
Not evaluated as a stand alone system.
Significant bias of 0.103 gph was detected during the evaluation.
Evaluator believes this bias was the result of product inflow into the tank
from valve leaks and product drain back from the pump return line and thus
evaluator did not use this bias in calculating above results.
Performance of the system can be improved by combining results of 2 or more
tests.
If this option is used, it is important to determine the number of tests,
their timing and the number of passing results necessary to confirm a tank
is tight.
The LRDP-24-5 (V1.1) combines the results of 5 tests and is one evaluated
option to improve the performance of this system. |
Vista Precision Solutions, Inc. |
Evaluator: Ken Wilcox
Associates |
2350 Lindberg Loop |
Tel: (816) 443-2494 |
Richland, WA 99354 |
Date of Evaluation: 01/29/99 |
Tel: (509) 943-2484 |
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