Ala. Admin. Code r. 335-6-15-.17

Current through Register Vol. 43, No. 1, October 31, 2024

Section 335-6-15-.17 - Methods Of Release Detection For Underground Storage Tanks

Each method of release detection for underground storage tanks used to meet the requirements of Rule 335-6-15-.15 must be conducted in accordance with the applicable requirements (a) through (i) of this rule. The Department may make a determination as to the capability of release detection equipment to meet the requirements of this rule.

(a)Inventory Control. Product inventory control (or another test of equivalent performance) must be conducted at least every 30 days to detect a loss or gain of at least 1.0 percent of flow-through plus 130 gallons on a 30 day basis in the following manner:

1. Inventory volume measurements for regulated substance inputs, withdrawals, and the amount still remaining in the underground storage tank are recorded each operating day;

2. The equipment used is capable of measuring the level of product over the full range of the underground storage tank's height to the nearest one-eighth of an inch;

3. The regulated substance inputs are reconciled with delivery receipts by measurement of the underground storage tank inventory volume before and after delivery;

4. Deliveries are made through a drop tube that extends to within one foot of the underground storage tank bottom;

5. Product dispensing is metered and recorded within the local standards for meter calibration or an accuracy of 6 cubic inches for every 5 gallons of product withdrawn; and

6. The measurement of any water or phase separated entrained water level in the bottom of the underground storage tank is made to the nearest one-eighth of an inch at least once every 30 days.

(b)Manual Tank Gauging. Manual tank gauging must meet the following requirements:

1. Underground storage tank liquid level measurements are taken at the beginning and ending of a period using the appropriate minimum duration of test value in the table shown in subparagraph (b)4. of this rule, during which no liquid is added to or removed from the underground storage tank;

2. Level measurements are based on an average of two consecutive stick readings at both the beginning and ending of the period;

3. The equipment used is capable of measuring the level of product over the full range of the underground storage tank's height to the nearest one-eighth of an inch;

4. A release is suspected and subject to the requirements of rules 335-6-15-.20 through 335-6-15-.23 if the variation between beginning and ending measurements exceed the weekly or 30 day standards in the following table:

Nominal Underground Storage Tank Capacity	Minimum Duration of Test	Weekly Standard (one test)	30 day Standard (average of 4 tests)
up to 550 gallons	36 hours	10 gallons	5 gallons
551-1,000 gallons (when underground storage tank diameter is 64")	44 hours	9 gallons	4 gallons
551-1,000 gallons (when underground storage tank diameter is 48")	58 hours	12 gallons	6 gallons
551-1,000 gallons (also requires periodic tank tightness testing)	36 hours	13 gallons	7 gallons
1001-2,000 gallons (also requires periodic tank tightness testing)	36 hours	26 gallons	13 gallons

5. Tanks of 550 gallons or less nominal capacity and tanks with a nominal capacity of 551 to 1,000 gallons that meet the tank diameter criteria in the table in paragraph (b)4 of this rule may use this as the sole method of release detection. All Emergency Power Generator tanks with a nominal capacity of 551 to 2,000 gallons may use the method in place of inventory control in paragraph (a) of this rule.

(c)Tank Tightness Testing. Tank tightness testing (or another test of equivalent performance) must be capable of detecting a 0.1 gallon per hour leak rate from any portion of the underground storage tank that routinely contains product while accounting for the effects of thermal expansion or contraction of the product, vapor pockets, underground storage tank deformation, evaporation or condensation, and the location of the water table.

1. The test must be performed by an individual having current certification of training from the manufacturer of the test method.

2. Unless waived by the Department the report of tightness testing of an underground storage tank must state whether or not the water table was above the base of the underground storage tank excavation pit at the time of testing and the method by which this determination was made. If it is above the base, the specific elevation of the water table shall be determined and recorded in the test report.

(d)Automatic Tank Gauging. Equipment for automatic tank gauging that tests for the loss of product and conducts inventory control must meet the following requirements:

1. The automatic product level monitor test can detect a 0.2 gallon per hour leak rate from any portion of the underground storage tank that routinely contains product;

2. The automatic tank gauging equipment must meet the inventory control requirements of subparagraph (a)6. of this rule (or other test of equivalent performance); and

3. The test must be performed with the equipment operating in one of the following modes:

(i) In-tank static testing conducted at least once every 30 days; or

(ii) Continuous in-tank leak detection operating on an uninterrupted basis or operating within a process that allows the equipment to gather incremental measurements to determine the leak status of the underground storage tank at least once every 30 days.

(e)Vapor Monitoring. Testing or monitoring for vapors within the soil gas of the excavation zone must meet the following technical and procedural requirements:

1. A vapor monitoring plan with any required plans and specifications, must be submitted to the Department for review by the Department. The plan must be sufficient to demonstrate compliance with the requirements of subparagraphs (e)2. through 8. of this rule or modifications may be required by the Department.

2. The materials used as backfill are sufficiently porous (e.g., gravel, sand, crushed rock) to readily allow diffusion of vapors from releases into the excavation area;

3. The stored regulated substance, or a tracer compound placed in the UST system, is sufficiently volatile (e.g., gasoline) to result in a vapor level that is detectable by the monitoring devices located in the excavation zone in the event of a release from the underground storage tank. The Department may require testing of a vapor monitoring system with a tracer compound where a system's reliability is in question.

4. The measurement of vapors by the monitoring device is not rendered inoperative by the groundwater, rainfall, or soil moisture or other known interferences so that a release could go undetected for more than 30 days;

5. The level of background contamination in the excavation zone will not interfere with the method used to detect releases from the UST system based upon information, to include volatile hydrocarbon concentrations, collected throughout the excavation zone where this method is proposed for use.

6. The vapor monitors and vapor monitoring wells are designed and operated in a manner sufficient to: detect any significant increase in concentration above background of the regulated substance stored in the UST system, a component or components of that substance, or a tracer compound placed in the UST system, and provide a vapor sample to the vapor monitor that is representative of the concentration in the excavation zone. Construction details shall comply with subparagraphs (e)7. through 13. of this rule.

7. The well casing shall be constructed of a material which is compatible with the substance stored; and which has sufficient strength to prevent structural failure.

8. The well casing shall be a minimum of 2 inches in diameter and shall be large enough for the chosen monitoring device to be installed or operated properly in the well. A low permeability backfill may require the use of larger diameter casing.

9. The length and slot size of the slotted portion of the casing should be sufficient to obtain a representative vapor sample in accordance with the depth of excavation zone and site hydrogeology.

10. The well screen should be surrounded by a clean filter pack which allows for passage of vapors while preventing passage of materials which could clog the well screen. The filter pack should extend 1 to 2 feet above the well screen.

11. An annular seal shall extend up from the top of the filter pack for 1 to 2 feet.

12. The well annulus shall be grouted from the top of the bentonite to the ground surface.

13. Monitoring wells shall have a watertight cap or enclosure at the ground surface.

14. In the UST excavation zone, the site is assessed to ensure compliance with the requirements in subparagraphs (e)2. through 5. of this rule and to establish the number and positioning of monitoring wells that will detect releases within the excavation zone from any portion of the underground storage tank that routinely contains product;

15. Vapor monitoring wells are clearly marked with the wording "NOT FOR DELIVERIES" or other sufficient language and locked to avoid unauthorized access and tampering. Monitoring wells which are located in an area subject to traffic must be equipped with enclosures which will not be damaged by normal traffic.

16. In the event of permanent closure of the UST system, all monitoring wells shall be closed according to a method acceptable to the Department, unless otherwise directed by the Department.

17. If a monitoring well is determined to be improperly constructed, closure may be required according to a method acceptable to the Department.

(f)Groundwater Monitoring. Testing or monitoring for liquids on the groundwater must meet the following technical and procedural requirements:

1. A groundwater monitoring plan with any required plans and specifications must be submitted for review. The plan must be sufficient to demonstrate that the requirements of subparagraphs (f)2. through 20. of this rule will be complied with or modifications may be required by the Department.

2. The regulated substance stored is immiscible in water and has a specific gravity of less than one;

3. The level of background contamination in or near the excavation zone will not interfere with the method used to detect releases from the UST system based upon information collected throughout the excavation zone and in the proposed area of well placement if not in the excavation zone;

4. Groundwater is never more than 20 feet from the ground surface and the hydraulic conductivity of the soil(s) between the UST system and the monitoring wells or devices is not less than 0.01 cm/sec (e.g., the soil should consist of gravels, coarse to medium sands, coarse silts or other permeable materials);

5. Monitoring wells used for the purpose of release detection by groundwater monitoring shall be constructed according to the requirements of subparagraphs (f)6. through 15. and 20. of this rule;

6. The well casing shall be a minimum of 2 inches in diameter when used for release detection. Monitoring wells installed for investigations may range from 1" to 2" and wells shall be 4 inches in diameter if installed for corrective action. All wells shall be constructed with only threaded connections between sections;

7. The well casing shall be constructed of a material which is compatible with the substance stored; and which has sufficient strength to prevent structural failure;

8. The well casing shall be slotted from the bottom to at least two feet above the normal annual high water table where the depth to water will allow, and shall be designed to prevent migration of natural soils or filter pack into the well and to allow entry of a regulated substance on the water table into the well under both high and low groundwater conditions;

9. The well casing shall extend at least five feet below the water level at the time of drilling but no deeper than 25 feet;

10. The well annulus shall be backfilled with an appropriate clean filter pack adjacent to the slotted casing;

11. An annular seal shall extend from the top of the filter pack for 2 to 5 feet, where the depth to water will allow;

12. The well annulus shall be grouted from the top of the bentonite seal to the ground surface;

13. Monitoring wells shall have a watertight enclosure or cap with a grouted collar at the ground surface;

14. Monitoring wells shall be developed upon drilling until the water is clear and relatively sand free by over pumping, bailing, or surging with compressed air;

15. Monitoring wells shall be as close to the excavation zone as is technically feasible. If a monitoring well is located within the excavation zone, the base of the excavation zone shall not be penetrated;

16. If a continuous monitoring device is not used, manual monitoring shall consist of removal of fluid from the well, using a bailer, or a sampler of similar design. The fluid shall be taken from the surface of the water table. The fluid shall:

(i) Be poured into a clean, clear glass container kept for the purpose, and examined for signs of an oily layer or odor of pollutant; or

(ii) Be tested at the site; or

(iii) Be sent to a laboratory and tested.

17. A monitoring well must contain at least 6 inches of water or a sufficient depth to allow a sample to be obtained using a sampler selected in accordance with subparagraph (f)16. of this rule. If this requirement cannot be met for more than 30 days, the Department may require the monitoring well to be replaced, or another method of monitoring to be proposed to the Department for review;

18. The continuous monitoring devices or manual methods used can detect the presence of at least one-eighth of an inch of free product on top of the groundwater in the monitoring wells;

19. Within and immediately below the UST system excavation zone, the site is assessed to ensure compliance with the requirements in subparagraphs (f)2. through 15. of this rule and to establish the number and positioning of monitoring wells or devices that will detect releases from any portion of the UST system that routinely contains product. This is to include an evaluation of the direction of the groundwater gradient at a site;

20. Monitoring wells are clearly marked with the wording "NOT FOR DELIVERIES" or other sufficient language and locked to avoid unauthorized access and tampering. Monitoring wells which are located in an area subject to traffic must be equipped with enclosures which will not be damaged by normal traffic;

21. In the event of permanent closure of the UST system, all monitoring wells shall be closed according to a method acceptable to the Department; and

22. If a monitoring well is determined by the Department to be improperly constructed, closure may be required according to a method acceptable to the Department.

23. Existing groundwater monitoring wells which were completed prior to April 5, 1989 will be authorized for continued use if the Department determines that the minimum criteria of the federal UST regulations for monitoring wells are satisfied and the existing wells do not pose a threat of groundwater contamination due to poor construction.

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

1. For double walled UST systems, the sampling or testing method can detect a leak through the inner wall in any portion of the underground storage tank that routinely contains product;

2. For UST systems with a secondary barrier within the excavation zone, the sampling or testing method used can in the determination of the Department, detect a leak between the UST system and the secondary barrier;

(i) The secondary barrier around or beneath the UST system consists of artificially constructed material that is sufficiently thick and impermeable (at least 10^-6 cm/sec for the regulated substance stored) to direct a leak to the monitoring point and permit its detection;

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

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

(iv) The groundwater, soil moisture, or rainfall will not render the testing or sampling method used 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 flood plain, unless the barrier and monitoring designs are for use under such conditions;

(vi) Monitoring wells are clearly marked with the wording "NOT FOR DELIVERIES" or other sufficient language and locked to avoid unauthorized access and tampering; and when located in areas which are subject to traffic must be equipped with enclosures which will not be damaged by normal traffic; and

(vii) Monitoring wells extend to within 6 inches of the secondary barrier but shall not contact the barrier.

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

(h)Statistical inventory reconciliation. Release detection methods based on the application of statistical principles to inventory data similar to those described in paragraph (a) of this rule must meet the following requirements:

1. Report a quantitative result with a calculated leak rate;

2. Be capable of detecting a leak rate of 0.2 gallon per hour or a release of 150 gallons within 30 days;

3. Use a threshold that does not exceed one-half the minimum detectible leak rate; and

4. Meet the inventory control requirements of subparagraphs (a)1. through 6. of this rule.

(i)Other methods. Any other type of release detection method, or combination of methods may be approved by the Department if:

1. It can detect a 0.2 gallon per hour leak rate or a release of 150 gallons within 30 days with a probability of detection of 0.95 and a probability of false alarm of 0.05; or

2. The owner and operator can demonstrate that the method can detect a release as effectively as any of the methods allowed in subparagraphs (c) through (h) above. In comparing methods, the Department shall 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 and operator must comply with any conditions imposed by the Department on its use to ensure the protection of human health and the environment.

Ala. Admin. Code r. 335-6-15-.17

Effective April 5, 1989. Amended: Filed July 2, 2007; effective August 6, 2007. Amended: Filed March 21, 2008; effective April 25, 2008. Amended: Filed December 12, 2011; effective January 16, 2012. Amended: Filed February 25, 2014; effective April 1, 2014.

Amended by Alabama Administrative Monthly Volume XXXVI, Issue No. 02, November 30, 2017, eff. 12/8/2017.

Amended by Alabama Administrative Monthly Volume XL, Issue No. 05, February 28, 2022, eff. 4/14/2022.

Author: Sonja Massey, Curt Johnson, Lee Davis, Latoya Hall, Dorothy Malaier

Statutory Authority:Code of Ala. 1975, § 22-36-3.