Underground Storage Tanks

How does the leak detection method work?

This method involves keeping the tank undisturbed for at least 36 hours each week, during which the tank's contents are measured, twice at the beginning and twice at the end of the test period. Manual tank gauging can be used as the sole method of leak detection for the life of the tank only for tanks up to 1,000 gallons. Tanks between 1,001 and 2,000 gallons can use this method only in combination with tank tightness testing. This combined method, however, can be used only during the first 10 years following tank installation.

The features of manual tank gauging are:

• Four measurements of the tank's contents must be taken weekly, two at the beginning and two at the end of at least a 36-hour period during which nothing is added to or removed from the tank (see "Table of Test Standards for Manual Tank Gauging").
• The average of the two consecutive ending measurements are subtracted from the average of the two beginning measurements to indicate the change in product volume.
• Every week, the calculated change in tank volume is compared to the standards shown in the "Table of Test Standards for Manual Tank Gauging" at the end of this page. If the calculated change exceeds the weekly standard, the UST may be leaking. Also, monthly averages of the four weekly test results must be compared to the monthly standard in the same way.

What are the regulatory requirements?

• Liquid level measurements must be taken with a gauge stick that is marked to measure the liquid to the nearest one-eighth of an inch.
• Manual tank gauging may be used as the sole method of leak detection for tanks with a capacity of 1,000 gallons or less for the life of the tank. Tanks between 551 and 1,000 gallons have two testing standards based on their diameter (see table). These tanks may use a combination of manual tank gauging and periodic tank tightness for the life of the tank (see table for testing standards).
• For tanks with a capacity of 1,001-2,000 gallons, manual tank gauging must be combined with periodic tightness testing. New tanks must be tightness tested every 5 years for 10 years following installation. Upgraded existing tanks must be tightness tested every 5 years for 10 years following upgrade. ("Upgraded" tanks have spill, overfill, and corrosion protection.) Existing tanks that have not been upgraded must be tightness tested every year until 1998. See Tank Tightness Testing for details on this method.
• Unless the tank is 1,000 gallons or less, this combined method will meet the federal requirements only temporarily (as explained above). You must eventually have another monitoring method that can be performed at least once a month.
• Tanks greater than 2,000 gallons in capacity may not use this method of leak detection to meet these regulatory requirements.

Will it work at your site?

Manual tank gauging is inexpensive and can be an effective leak detection method when used as described above with tanks of the appropriate size.

Anything else you should consider?

You can perform manual tank gauging yourself. Correct gauging, recording, and interpretation are the most important factors for successful tank gauging. The accuracy of tank gauging can be greatly increased by spreading product-finding paste on the gauge stick before taking measurements.

Will you be in compliance?

NOTE: Manual tank gauging can only be used for smaller tanks. Tanks 1,000 gallons or less can use this method alone, but tanks from 1,001-2,000 gallons can only use manual tank gauging when it is combined with tank tightness testing. Manual tank gauging cannot be used for tanks over 2,000 gallons. When performed according to recommended practices, manual tank gauging meets the federal leak detection requirements for USTs with a capacity of 1,000 gallons or less for the life of the tank.

More Information On Manual Tank Gauging

OUST has a booklet available from our web site, Manual Tank Gauging: For Small Underground Storage Tanks, that clearly explains how to do manual tank gauging with simple step-by-step directions. The booklet also includes standard forms used to record inventory data.

Table of Test Standards for Manual Tank Gauging

Tank Size	Minimum Duration of Test	Weekly Standard (1 test)	Monthly Standard (4-test average)
up to 550 gallons	36 hours	10 gallons	5 gallons
551-1,000 gallons (when tank diameter is 64")	44 hours	9 gallons	4 gallons
551-1,000 gallons (when tank diameter is 48")	58 hours	12 gallons	6 gallons
551-1,000 gallons (also requires periodic tank tightness testing)	36 hours	13 gallons	7 gallons
1,001-2,000 gallons (also requires periodic tank tightness testing)	36 hours	26 gallons	13 gallons

Top of page