Sec. 26.10.05.04. Method of Release Detection  


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  • A. Owners and operators shall perform daily inventory control as described in COMAR 26.10.04.01. In addition, one of the following methods of release detection shall be performed on a monthly basis.

    B. Statistical Inventory Reconciliation.

    (1) Product inventory control, or another test of equivalent performance, shall be conducted monthly to detect a release with a probability of detection of at least 0.95 and a probability of false alarm of at most 0.05.

    (2) Detection level shall be:

    (a) 0.2 gallon per hour leak rate; or

    (b) 150 gallons within a month.

    (3) Statistical inventory reconciliation shall be performed in the following manner:

    (a) Inventory volume measurements shall be performed in accordance with COMAR 26.10.04.01E and F; and

    (b) Records are reviewed on a monthly basis by a Department-approved third party to reconcile for inventory variations.

    C. Manual Tank Gauging.

    (1) Manual tank gauging using equipment maintained in good operating condition, and capable of measuring the level of oil over the full range of the tank's height to the nearest 1/8 inch, shall be performed as follows:

    (a) Tank liquid level measurements shall be taken at the beginning and ending of a period of at least 36 hours during which liquid may not be added to or removed from the tank;

    (b) Level measurements shall be based on an average of two consecutive stick readings at both the beginning and ending of the period; and

    (c) A release is indicated and subject to the requirements of COMAR 26.10.08 if the variation between beginning and ending measurements exceeds the weekly or monthly standards in the following table:

    Nominal Tank Capacity Weekly Standard (one test) Monthly Standard (average of four tests)
    550 gallons or less 10 gallons 5 gallons
    551-1,000 gallons 13 gallons 7 gallons
    1,001-2,000 gallons 26 gallons 13 gallons

    (2) Only tanks of 550 gallons or less nominal capacity may use manual tank gauging as the sole method of release detection. Tanks of 551 to 2,000 gallons may use manual tank gauging, but only in conjunction with precision tightness testing or hydrostatic testing conducted every 5 years as permitted under COMAR 26.10.07. Tanks of greater than 2,000 gallons nominal capacity may not use this method to meet the requirements of this chapter.

    D. Precision Tightness Testing.

    (1) The precision test method as defined under COMAR 26.10.02.04 may be used.

    (2) When a precision test is performed, the following table shall be used to determine UST system tightness:

    Tanks greater than (gals.) and Up to and Including (gals.) Criterion (gph)
    0 12,500 0.05
    12,500 17,500 0.063
    17,500 22,500 0.075
    22,500 27,500 0.088
    27,500 32,500 0.100
    32,500 37,500 0.113
    37,500 42,500 0.125
    42,500 47,500 0.138
    47,500 greater 0.150

    (3) Only tests and testing procedures approved by the Department shall be used.

    (4) UST systems with an inconclusive test shall be retested within 2 working days.

    (5) A second inconclusive test shall be reported to the Department as a failure.

    E. Automatic Tank Gauging. Equipment for automatic tank gauging that tests for the loss of regulated substance and conducts inventory control shall meet the following requirements:

    (1) The automatic regulated substance level monitor test shall be capable of detecting a 0.2 gallon per hour leak rate from any portion of the tank that routinely contains a regulated substance; and

    (2) Inventory control, or another test of equivalent performance, is conducted in accordance with the requirements of §B of this regulation.

    F. Vapor monitoring is not an acceptable method of release detection and may not be used after April 1, 2009 unless approved under §I of this regulation.

    G. Ground Water Monitoring. An assessment shall be performed 60 days before the implementation of this method. A written report of this assessment shall be provided to the Department upon request and shall demonstrate that the testing or monitoring to detect a regulated substance on the ground water shall meet all of the following requirements:

    (1) The regulated substance stored is immiscible in water and has a specific gravity of less than one;

    (2) Ground water is never more than 15 feet from the ground surface and the hydraulic conductivity of the soil or soils between the UST system and the monitoring wells or devices is not less than 0.01 centimeter/second, with the soil consisting of gravels, coarse to medium sands, coarse silts, or other permeable materials;

    (3) The slotted portion of the monitoring well casing shall be designed to prevent migration of natural soils or filter pack into the well and to allow entry of regulated substance on the water table into the well under both high and low ground water conditions;

    (4) Monitoring wells shall be sealed from the ground surface to the top of the filter pack;

    (5) Monitoring wells or devices shall intercept the UST excavation zone or be positioned as close to it as is technically feasible;

    (6) The method of measuring the contents of the well, whether automatic or manual, shall be capable of detecting the presence of at least 1/8 of an inch of free product on top of the ground water in the monitoring wells;

    (7) Within and immediately below the UST system excavation zone, the site is assessed to ensure compliance with the requirements in §G(1)-(5) of this regulation and to establish the number and positioning of monitoring wells or devices that will detect releases from any portion of the tank that routinely contains a regulated substance;

    (8) Monitoring wells are clearly marked and secured to avoid unauthorized access and tampering;

    (9) A key, a lock combination number, or access tool for all monitoring wells is provided to the Administration upon request and made available on the site where the UST system is located.

    H. Interstitial Monitoring. Interstitial monitoring between the UST system and a secondary barrier immediately around or beneath it shall be used, but only if the system is designed, constructed, and installed to detect a leak from any portion of the tank that routinely contains a regulated substance and also meets one of the following requirements:

    (1) For double-walled UST systems, the sampling or testing method can detect a release through the inner wall in any portion of the tank that routinely contains a regulated substance;

    (2) For UST systems with a secondary barrier within the excavation zone, the sampling or testing method used can detect a release between the UST system and the secondary barrier provided that:

    (a) The secondary barrier around and beneath the UST system consists of artificially constructed material that is sufficiently thick and impermeable, at least 1 × 10-6 centimeter/second for the regulated substance stored, to direct a release to the monitoring point and permit its detection;

    (b) The barrier is compatible with the regulated substance stored so that a release from the UST system will not cause a deterioration of the barrier allowing a release to pass through undetected;

    (c) For cathodically protected tanks, the secondary barrier shall be installed so that it does not interfere with the proper operation of the cathodic protection system;

    (d) The ground water, soil moisture, or rainfall will not make the testing or sampling method used inoperative so that a release could go undetected for more than 30 consecutive days;

    (e) The site is assessed to ensure that the secondary barrier is always above the ground water and not in a 25-year flood plain, unless the barrier and monitoring designs are for use under these conditions; and

    (f) Monitoring wells are clearly marked and secured with bolts or a lock to avoid unauthorized access and tampering.

    (3) For tanks with an internally fitted liner, an automated device can detect a release between the inner wall of the tank and the liner, and the liner is compatible with the substance stored.

    I. Other Methods. Any other type of release detection method, or combination of methods, can be used if approved by the Department, if:

    (1) It can detect a 0.2 gallon per hour leak rate or a release of 150 gallons within a month with a probability of detection of at least 0.95 and a probability of false alarm of at most 0.05; or

    (2) The owner and operator can demonstrate to the Department that the method can detect a release as effectively as any of the methods allowed in §§D-H of this regulation and in this section.

    J. If the method in §I(2) of this regulation is approved, the owner and operator shall comply with any conditions imposed by the Department on its use to ensure the protection of human health and the environment.