UST Technical Compendium Category 3: Release Detection (RD)
http://epa.gov/oust/compend/rd.htm

Question 21: If a facility is using statistical inventory reconciliation (SIR) monthly and a report is not conclusive, is the owner/operator out of compliance?
Answer: Yes, an UST system relying on monthly SIR with a report that does not conclusively indicate whether the system is leaking at 0.2 gallons per hour with a probability of detection of 0.95 and a probability of false alarm of 0.05 is not technically compliance with the release detection requirements. A lack of conclusive results may not be possible on a small percentage of tank data each month, for several reasons.  Because of this, EPA encourages States and Regions to use discretion, and to consider the efforts of owners and operators to comply in assessing whether or not enforcement is carried out. 
[November 18, 1993 memorandum to State and Regional Program Managers (PDF) (2 pp, 11K)] 
[February 7, 1994 letter to Mr. Hunt (PDF) (3pp, 14K)]


