Title 18 . Environmental Conservation

Chapter 78 . Administrative Enforcement

Section 65. Release detection methods and monitoring for tanks

18 AAC 78.065. Release detection methods and monitoring for tanks

(a) Each method of release detection for tanks that is used to meet the requirements of 18 AAC 78.060 and 18 AAC 78.070 must meet the requirements of this section. Using one method or a combination of the methods listed in this section, an owner or operator shall monitor each tank for releases at least once every 30 days.

(b) Inventory control. Inventory control must be capable of detecting a release of at least 1.0 percent of flow-through plus 130 gallons monthly. Inventory control must be conducted monthly as follows:

(1) inventory volume measurements are recorded each operating day for petroleum

(A) inputs;

(B) withdrawals; and

(C) amount remaining in the tank;

(2) the equipment used is capable of measuring the level of petroleum over the full range of the tank's height to the nearest one-eighth of an inch;

(3) at the time of delivery, inputs of petroleum are reconciled with delivery receipts, by measurement of the tank inventory volume before and after delivery;

(4) deliveries are made through a drop tube that extends to within one foot of the tank bottom;

(5) dispensing is metered and recorded within state standards for meter calibration;

(6) at least once a month, the measurement of any water level in the bottom of the tank is made to the nearest one-eighth of an inch; and

(7) the information generated under this subsection must be reviewed and analyzed monthly by the owner or operator.

(c) Manual tank gauging. Manual tank gauging as a release detection method may be used in the following circumstances:

(1) for tanks of 1,000 gallons or less nominal capacity, only if

(A) tank liquid level measurements are taken at the beginning and end of a time period set out in Table A of this subsection, during which no liquid is added to or removed from the tank;

(B) level measurements are based on the average of two consecutive stick readings at the beginning and the end of the appropriate period in Table A;

(C) the equipment used is capable of measuring the level of product over the full range of the tank's height to the nearest one-eighth of an inch; and

(D) testing is conducted at least once each week, and the four weekly results are averaged to obtain a monthly result; if the variation between the beginning and ending measurements exceeds the weekly or monthly standards in Table A, a leak is suspected, and the owner or operator is subject to 18 AAC 78.200 - 18 AAC 78.280;

TABLE A Monthly Weekly Standard Minimum Nominal Tank Standard (average of Test Capacity (one test) four tests) Duration) 550 gallons or less 10 gallons 5 gallons 36 hours 551 - 999 gallons 13 gallons 7 gallons 36 hours 1,000 gallons 9 gallons 4 gallons 44 hours (64" X 73") 1,000 gallons 12 gallons 6 gallons 58 hours (48" X 128") 1,001 - 2,000 26 gallons 13 gallons 36 hours gallons

(2) for tanks of 1,001 - 2,000 gallons nominal capacity in combination with tank tightness testing under (d) of this section, instead of monthly inventory control; and

(3) for tanks of greater than 2,000 gallons nominal capacity, never.

(d) Tank tightness testing. Tank tightness testing, or another test of equal performance, must be capable of detecting a 0.1 gallon per hour leak rate from any part of a tank, including the associated piping, that routinely contains petroleum, while accounting for the effects of thermal expansion or contraction of the petroleum, vapor pockets, tank deformation, evaporation or condensation, and the location of the water table. To satisfy the requirements of this subsection, the owner or operator may use only tank tightness tests that have been developed and reviewed by a nationally-recognized association or third-party testing laboratory and that meet or exceed the criteria for the detection of leaks set out in the United States Environmental Protection Agency's manuals Standard Test Procedures for Evaluating Leak Detection Methods: Volumetric Tank Tightness Testing Methods, March 1990 (EPA/530/UST - 90/004), and Standard Test Procedures for Evaluating Leak Detection Methods: Nonvolumetric Tank Tightness Testing Methods, March 1990 (EPA/530/UST - 90/005), the provisions of which are adopted by reference. The tests required by this subsection must be performed by a person certified under this chapter. The owner or operator shall submit to the department a certified copy of the evaluation results indicating that the criteria have been met or exceeded and a copy of the manufacturer's test protocol. An owner or operator may use tank tightness testing only if the UST meets the performance standards set out in 18 AAC 78.025 or 18 AAC 78.030 and the owner or operator complies with the monthly inventory control requirements set out in (b) of this section or the manual tank gauging requirements set out in (c) of this section. If tank tightness testing is used, the test must be conducted every five years for ten years after the tank is installed or upgraded, whichever is later. The department may disapprove a tank tightness test or testing system under this subsection if the

(1) test or testing system fails to disclose leaks that fall within the boundaries of the criteria stated in this subsection; or

(2) tester is not certified by the manufacturer of the test or testing system.

(e) Automatic tank gauging. Equipment for automatic tank gauging that tests for the loss of petroleum or that conducts inventory control must be capable of detecting

(1) a 0.2 gallon per hour leak rate from any part of the tank that routinely contains petroleum; and

(2) a release of 150 gallons within a 30-day period, with a probability of detection of 95 percent and a probability of false alarm of five percent.

(f) Soil gas vapor monitoring. Vapor monitoring may be used only at certain sites and only with department approval. The department will, in its discretion, approve the testing or monitoring of soil gas vapors in the excavation zone if the following requirements are met:

(1) material used as backfill is sufficiently porous to readily allow diffusion of vapors from a release into the excavation area; for purposes of this paragraph, gravel, sand, or crushed rock are "sufficiently porous" materials;

(2) the stored petroleum, or a tracer compound placed in the tank system, is sufficiently volatile to result in a vapor level that is detectable by the monitoring devices located in the excavation zone if a release from the tank occurs; for purposes of this paragraph, gasoline is "sufficiently volatile;"

(3) the measurement of vapors by the monitoring device is not rendered inoperative by groundwater, rainfall, soil moisture, other local climatological, geologic, or hydrogeologic conditions, or other known interference so that a release could go undetected for more than 30 days;

(4) the level of background contamination in the excavation zone will not interfere with the method used to detect a release from the tank;

(5) the vapor monitors are designed and operated to detect any significant increase in concentration above background of

(A) petroleum stored in the tank system;

(B) a component or components of the petroleum; or

(C) a tracer compound placed in the tank system;

(6) the UST excavation zone is assessed as required by 18 AAC 78.090 to

(A) ensure compliance with (1) - (4) of this subsection; and

(B) establish the number and positioning of observation wells that will detect a release within the excavation zone from any part of a tank that routinely contains petroleum; and

(7) observation wells are clearly marked and secured to avoid unauthorized access and tampering.

(g) Groundwater monitoring. Groundwater monitoring may be used only if the groundwater is never more than 20 feet from the ground surface and only with department approval.

(h) Interstitial monitoring. Interstitial monitoring between the UST or pipe and a secondary barrier immediately around or beneath the UST or pipe may be used only if the system

(1) is designed, constructed, and installed to detect a leak from any part of a tank or pipe that routinely contains petroleum; and

(2) meets one of the following requirements:

(A) for a double-walled UST, including piping, the sampling or testing method is capable of detecting a release through the inner wall in any part of a tank or pipe that routinely contains petroleum;

(B) for a UST with a secondary barrier within the excavation zone, the sampling or testing method used is capable of detecting a release between the UST and the secondary barrier as follows:

(i) the secondary barrier around or beneath the UST consists of artificially constructed material that is sufficiently thick and impermeable to direct a release to the monitoring point and permit its detection; for purposes of this clause, "sufficiently thick and impermeable" means have a permeability of at least 10 -6 cm/sec for the petroleum stored;

(ii) the barrier is compatible with the petroleum stored so that a release from the UST will not cause a deterioration of the barrier and allow a release to pass through undetected;

(iii) for a cathodically protected tank, the secondary barrier must be installed so that it does not interfere with proper operation of the cathodic protection system;

(iv) groundwater, soil moisture, or rainfall will not render the testing or sampling method inoperative so that a release could go undetected for more than 30 days;

(v) the site is assessed to ensure that the secondary barrier is always above the groundwater and not in a 25-year floodplain, unless the barrier and monitoring designs are for use under those conditions; and

(vi) monitoring wells are clearly marked and secured to avoid unauthorized access and tampering; or

(C) for a tank with an internally fitted liner, an automated device is capable of detecting a release between the inner wall of the tank and the liner, and the liner is compatible with the substance stored.

(i) Statistical inventory reconciliation. Statistical inventory reconciliation methods that analyze inventory records for the loss of petroleum and that are intended as a release detection method must meet the following requirements:

(1) the statistical analysis must be capable of detecting a 0.2 gallon per hour leak rate from any part of the tank that routinely contains petroleum; and

(2) the collection of inventory data must meet the requirements of (b) of this section.

(j) Other methods. Any other type of release detection method, or combination of such other methods, may be used with prior approval, if the method or combination of methods can, for volumetric release detection methods, detect a 0.2 gallon per hour leak rate or a release of 150 gallons in a 30-day period with a probability of detection of 95 percent and a probability of a false alarm of five percent. For non-volumetric release detection methods, the department may approve another method of release detection not described in (d) - (i) of this section, if the owner or operator shows that the method can detect a release as effectively as any of the methods allowed in (d) - (i) of this section. In comparing methods, the department will consider the size of release that the method can detect and the frequency and reliability with which it can be detected. If the method is approved, the owner or operator shall comply with any conditions imposed by the department on its use to ensure the protection of human health and safety and the environment.

(k) Certification of performance standards. The National Work Group on Leak Detection Evaluations' List of Leak Detection Evaluations for Underground Storage Tank (UST) Systems, Ninth Edition, November 21, 2001, shall be used to determine compliance with the applicable performance standards for automatic tank gauging, statistical inventory reconciliation, tightness testing, electronic interstitial monitoring, and automatic line leak detectors. The List of Leak Detection Evaluations for Underground Storage Tank (UST) Systems, Ninth Edition, November 21, 2001, is adopted by reference.

History: Eff. 3/25/91, Register 118; am 8/21/91, Register 119; am 11/3/95, Register 136; am 6/25/99, Register 150; am 1/30/2003, Register 165

Authority: AS 46.03.020

AS 46.03.365

AS 46.03.375

Editor's note: 1. Practices described in the American Petroleum Institute Recommended Practice 1621, Bulk Liquid Stock Control at Retail Outlets , Fifth Edition, May 1993, may be used, if applicable, as guidance in meeting the requirements of (b)(6) of this section.

2. The provisions outlined in the Steel Tank Institute's Standard for Dual Wall Underground Steel Storage Tanks, F841-01, revised June 1, 2001, may be used as guidance for aspects of the design and construction of underground steel double-walled tanks as described in (h)(2)(A) of this section.

3. The information described in the United States Environmental Protection Agency's document Detecting Leaks, Successful Methods Step-by-Step, Chapter 4, November 1989 (EPA/530/UST-89/012), may be used as guidance for tank tightness testing.

4. The National Work Group on Leak Detection Evaluations' List of Leak Detection Evaluations for Underground Storage Tank (UST) Systems, Ninth Edition, November 21, 2001, may be reviewed at the Department of Environmental Conservation's offices in Anchorage, Fairbanks, Juneau, and Soldotna or may be obtained on the Internet at http://www.nwglde.org.

5. The tank tightness documents referred to in Notes 1 and 2 are on file in the Office of the Lieutenant Governor and may be reviewed at the Department of Environmental Conservation's offices in Anchorage, Fairbanks, Juneau, and Soldotna or may be obtained from the publisher at the address listed in the editor's note at 18 AAC 78.025.

6. The United States Environmental Protection Agency tank tightness testing documents referred to in Note 3 and in 18 AAC 78.065(d) are on file in the Office of the Lieutenant Governor and may be reviewed at the Department of Environmental Conservation's offices in Anchorage, Fairbanks, Juneau, and Soldotna or may be obtained from:

United States Environmental Protection Agency (EPA), Office of Underground Storage Tanks, 401 M St., SW, Mail Code 54-02W, Washington, D.C. 20460; phone (703) 308-8850; Fax: (703) 308-8505; URL: http://www.epa.gov/;

United States Government Bookstore, Room 194 Federal Building, 915 Second Avenue, Seattle, Washington 98174; phone: (206) 553-4270; Fax: (206) 553-6717; URL: http://bookstore.gpo.gov/.