Ground water monitoring
Secondary containment with interstitial monitoring
Automatic tank gauging systems
Tank tightness testing and inventory control
Manual tank gauging
Leak detection for underground suction piping
Leak detection for pressurized underground piping
Statistical inventory reconciliation
Manual Tank Gauging
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.
If you are considering using manual tank gauging to meet the Federal UST leak detection requirements, this section provides information about its appropriate use. This method should not be confused with inventory control, described earlier.
Will I be in compliance?
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. (For additional leak detection requirements for piping, see the following sections on leak detection for piping.)
You should find out if state or local requirements have limitations on the use of manual tank gauging or have requirements that are different from those presented below.
How does it work?
- Four liquid level measurements 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.
- 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 below. 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.
|Tank Capacity||Weekly Standard (one test)||Monthly Standard (4-test average)||Minimum Duration of Test|
|If Manual Tank Gauging is the ONLY leak detection method used.|
|up to 550gallons||10gallons||5 gallons||36 hours|
|551 - 1,000 gal. (when largest tank is 64' x 73')||9 gallons||4 gallons||44 hours|
|1,000 gal. (if tank is 48'x 128')||12 gallons||6 gallons||58 hours|
|If Manual Tank Gauging is combined with Tank Tightness Testing:|
|1,001 - 2,000 gal.||26 gallons||13 gallons||36 hours|
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.
- For tanks with a capacity of 1,001 - 2,000 gallons, manual tank gauging must be combined with tightness testing according to the schedule below. See the earlier section on tank tightness testing for details on this method.
|MINIMUM TESTING FREQUENCY|
|New tanks||Every 5 years for 10 years following installation|
|Existing tanks, upgraded *||Every 5 years for 10 years following upgrade|
|Existing tanks, not upgraded||Every year until 1998|
|* Upgraded tanks have corrosion protection and spill/overfill prevention devices.|
Note that this combined method will meet the Federal requirements only temporarily. After the applicable time period listed above, you must have a monitoring method that can be performed at least once a month. See the other sections for allowable monthly monitoring options.
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 my 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.
What other information do I need?
You can perform manual tank gauging yourself. Correct gauging, recording and interpretation are the most important factors for successful tank gauging.
Your product supplier, jobber or contractor can probably teach you the proper technique for manual tank gauging, and may be able to supply you with recording forms and a gauge stick.
The accuracy of tank gauging can be greatly increased by spreading product-finding paste on the gauge stick before taking a measurement.
How much does it cost?
For tanks less than 1,001 gallons, the only costs are the price of a gauge stick and perhaps some product-finding paste. These costs are nominal (less than $200).
For tanks between 1,001-2,000 gallons, there is the additional cost of periodic tank tightness testing. These costs are highly variable (from about $250 to over $1,000 for each test).