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
Statistical Inventory Reconciliation
Will I be in compliance?
Statistical inventory reconciliation (SIR), when performed according to the vendor's specifications, meets Federal leak detection requirements for new and existing underground storage tanks (USTs) and piping as follows. SIR with a 0.2 gallon per hour leak detection capability meets the federal requirements for monthly monitoring for the life of the tank and piping. SIR with a 0.1 gallon per hour leak detection capability meets the Federal requirements as an equivalent to tank tightness testing. SIR could, in some cases, meet the Federal requirements for line tightness testing as well. (For additional leak detection requirements for piping, see the sections on leak detection for piping.) You should find out if there are state or local limitations on the use of SIR or requirements that are different from those presented below.
How does it work?
Statistical inventory reconciliation analyzes inventory, delivery, and dispensing data collected over a period of time to determine whether or not a tank system is leaking.
Each operating day, you measure the product level using a gauge stick or other tank level monitor. You also keep complete records of all withdrawals from the UST and all deliveries to the UST. After data have been collected for the period of time required by the SIR vendor, you provide the data to the SIR vendor.
The SIR vendor uses sophisticated computer software to conduct a statistical analysis of the data to determine whether or not your UST may be leaking. The SIR vendor provides you with a test report of the analysis results.
What are the regulatory requirements?
To be allowable as monthly monitoring, a SIR method must be able to detect a leak at least as small as 0.2 gallons per hour and meet the Federal regulatory requirements regarding probabilities of detection and false alarm. Data must be submitted monthly.
To be allowable as an equivalent to tank tightness testing, a SIR method must be able to detect a leak at least as small as 0.1 gallons per hour and meet the Federal regulatory requirements regarding probabilities of detection and false alarm.
The individual SIR method must have been evaluated with a test procedure to certify that it can detect leaks at the required level and with the appropriate probabilities of detection and false alarm.
If the monthly test report is inconclusive, you must take the steps necessary to find out conclusively whether your tank is leaking.
You must keep on file both the test reports and the documentation that the SIR method used is certified as valid for your UST system.
Will it work at my site?
Generally, few product or site restrictions apply to the use of SIR:
- A SIR method may be used on tanks with up to 1.5 times the volume at which that method was evaluated. If you are considering using a SIR method for tanks greater than 18,000 gallons, discuss its applicability with the vendor.
- Water around a tank may hide a hole in the tank or distort the data to be analyzed by temporarily preventing a leak. To detect a leak in this situation, you must check for water at least once a month.
What other information do I need?
Data, including product level measurements, dispensing data, and delivery data, should all be carefully collected according to the SIR vendor's specifications. Poor data collection may produce inconclusive results and noncompliance.
The SIR vendor will generally provide forms for recording data, a calibrated chart converting liquid level to volume, and detailed instructions on conducting measurements.
Statistical inventory reconciliation should not be confused with other release detection methods that also rely on periodic reconciliation of inventory, withdrawal, or delivery data. Unlike manual tank gauging, automatic tank gauging systems, or inventory control, SIR uses a sophisticated statistical analysis of data to detect releases. This analysis can only be done by competent vendors of certified SIR methods.
You should "shop around," ask questions, get recommendations, and select a method and company that meet the needs of your site.
How much does it cost?
There are no installation costs. Equipment costs are minimal, although you should ensure that dispensing meters are in calibration and that your gauge stick or other tank level monitor is in good condition. Annual costs for the service may depend on your data quality, how you provide data to the vendor (paper, diskette, or modem) and the number of tanks and sites you have. Possible costs for a typical station with three tanks:
- Used as a monthly monitoring method (with 0.2 gallon per hour leak detection capability), SIR could cost $840 to $1200 yearly; or
- Used as the equivalent to tank tightness testing (with 0. 1 gallon per hour leak detection capability), SIR could cost $225 to $540, to test three tanks one time. Testing piping as well with SIR may add cost.