Ariz. Admin. Code § R18-12-243 - Methods of Release Detection for Tanks

A. If inventory contro l is used to meet the requirements of R18-12-241, it shall be used in conjunction with tank tightness testing described in subsection (C). Inventory control shall be conducted monthly in accordance with R18-12-281(O) to detect a release of at least 1.0% of flow-through plus 130 gallons on a monthly basis in the following manner:

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

2. The equipment used is capable of measuring the level of the regulated substance over the full range of the tank's vertical dimension to the nearest 1/8 of an inch;

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

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

5. Dispensing of regulated substances is metered and recorded within the standards established by the entity with jurisdiction. If no standards are established, dispensing which meets an accuracy of six cubic inches for every five gallons of regulated substance withdrawn shall be used;

6. The measurement of any water level in the bottom of the tank is made to the nearest 1/8 of an inch at least once a month;

7. Inventory control shall not be utilized as the sole method of release detection.

B. Manual tank gauging used to meet the requirements of R18-12-241 shall meet all of the following requirements:

1. Tank liquid level measurements are taken at the beginning and ending of a period equal to the appropriate minimum duration of test in the table below during which no liquid is added to or removed from the UST system;

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 regulated substance over the full range of the tank's vertical dimension to the nearest 1/8 of an inch;

4. A release is suspected and subject to the requirements of A.R.S. § 49-1004 and the rules promulgated thereunder if the variation between beginning and ending measurements exceeds the weekly or monthly standards in the following table:

Nominal Tank Capacity	Minimum duration of test	Weekly standard (1 test)	Monthly standard (average of 4 tests)
550 gallons or less	36 hours	10 gallons	5 gallons
551-1,000 gallons (when tank diameter is 64 inches)	44 hours	9 gallons	4 gallons
551-1,000 gallons (when tank diameter is 48 inches)	58 hours	12 gallons	6 gallons
551-1,000 gallons (also requires periodic tank tightness testing)	36 hours	13 gallons	7 gallons
1,001-2,000 gallons (also requires periodic tank tightness testing)	36 hours	26 gallons	13 gallons

5. Manual tank gauging may be used as the sole method of release detection only for tanks of 550 gallons or less capacity and tanks with a nominal capacity of 551 to 1,000 gallons that meet the tank diameter criteria in the table in subsection (B)(4) of this Section. Manual tank gauging may be used in place of inventory control in subsection (A) for all other tanks of 551 to 2,000 gallons. This method shall not be used to meet the requirements of R18-12-241 for tanks of greater than 2,000 gallons capacity.

C. Tank tightness testing shall be capable of detecting a 0.1 gallon per hour leak rate from any portion of the tank that routinely contains a regulated substance while accounting for the effects of thermal expansion or contraction of the regulated substance, vapor pockets, tank deformation, evaporation or condensation, and the location of the water table.

D. Equipment for automatic tank gauging that tests for the loss of regulated substance and conducts inventory control used to meet the requirements of R18-12-241 shall meet all of the following requirements:

1. The automatic regulated substance level monitor test shall be performed at least monthly and be capable of detecting a 0.2 gallon per hour leak rate from any portion of the tank that routinely contains regulated substance,

2. The automatic tank gauging equipment shall meet the inventory control (or other test of equivalent performance) requirements of subsection (A), and

3. The test shall be performed with the system operating in one of the following modes:

a. In-tank static testing conducted at least once monthly; or

b. Continuous in-tank leak detection operating on an uninterrupted basis or operating within a process that allows the system to gather incremental measurements to determine the leak status of the tank at least once monthly.

E. Testing or monitoring for vapors within the soil gas of the excavation zone used to meet the requirements of R18-12-241 shall be conducted at least monthly and shall meet all of the following requirements:

1. In the UST excavation zone, the site is assessed to ensure that the leak detection method will comply with the requirements in subsections (E)(2) through (6);

2. The leak detection system is constructed and designed so that the number and positioning of monitoring wells will detect releases into the excavation zone from any portion of the system which routinely contains a regulated substance within 30 days from the date of commencement of a release;

3. The stored regulated substance, or a tracer compound placed in the UST system, will produce a vapor level that is detectable by the monitoring devices in the monitoring wells within 30 days from the date of commencement of a release from the UST system;

4. The materials used as backfill will allow diffusion of vapors from releases into the excavation area such that a release is detected within 30 days from the date of commencement of a release from the UST system;

5. The groundwater, rainfall, soil moisture, or other known interferences will not render the measurement of vapors by the monitoring device inoperable so that a release could go undetected by the monitoring devices in the monitoring wells for more than 30 days from the date of commencement of the release from the UST system;

6. The level of background contamination at the site will not interfere with the method used to detect releases from the tank system;

7. The vapor monitors are designed and operated to detect any significant increase in concentration above a documented background level of the regulated substance stored in the tank system, a component or components of that substance, or a volatile tracer compound placed in the tank system;

8. Monitoring wells are clearly marked and secured to avoid unauthorized access and tampering.

F. Testing or monitoring for liquids on the groundwater used to meet the requirements of R18-12-241 shall be conducted monthly and meet the following requirements:

1. Within and immediately below the UST excavation zone, the site is assessed to ensure that the leak detection method will comply with the requirements in subsections (F)(2) through (7);

2. The leak detection system shall be constructed and designed so that the number and positioning of monitoring wells or devices will detect releases into the excavation zone from any portion of the system which routinely contains a regulated substance;

3. The regulated substance stored is immiscible in water and has a specific gravity of less than 1;

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

5. Monitoring wells or devices intercept the excavation zone or are as close to it as is technically feasible;

6. 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;

7. Monitoring wells shall be sealed from the ground surface to the top of the filter pack;

7 8. The continuous monitoring devices or manual methods used can detect the presence of at least 1/8 of an inch of free product on top of the groundwater in the monitoring wells;

8. Monitoring wells shall be sealed from the ground surface to the top of the filter pack;

9. Monitoring wells are clearly marked and secured to avoid unauthorized access and tampering.

G. Interstitial monitoring between the UST system and a secondary barrier immediately around or beneath it which is used to meet the requirements of R18-12-241 shall be conducted at least monthly and shall be designed, constructed and installed to detect a leak from any portion of the UST system that routinely contains a regulated substance, and shall meet one of the following requirements:

1. For double-walled UST systems, the sampling or testing method shall be able to detect a leak through the inner wall in any portion of the UST system that routinely contains a regulated substance.

2. For UST systems with a secondary barrier within the excavation zone, characteristics of the site and system components shall be designed and constructed to detect a leak between the UST system and the secondary barrier and shall meet all of the following requirements:

a. The secondary barrier around or beneath the UST system shall be constructed of synthetic materials which are sufficiently thick and impermeable to prevent structural weakening of the secondary barrier as a result of contact with any released regulated substance. The rate of permeability shall not exceed 10^-6 centimeters per second for the regulated substance stored. In addition, the secondary barrier shall be capable of directing any leak to the monitoring point and permit its detection;

b. 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;

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

d. 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;

e. The characteristics of the UST site are 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;

f. Monitoring wells are clearly marked and secured to avoid unauthorized access and tampering.

3. For tanks with an internally fitted liner, an automated device shall be able to detect a leak between the inner wall of the tank and the liner, and the liner shall be 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 R18-12-243(A) shall 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; and

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

H I. Any other type of release detection method, or combination of methods, may be used to meet the requirements of R18-12-241 if all of the following requirements are met:

1. The monitoring is conducted at least monthly;

2. The Department determines that the method meets either of the following requirements:

a. The method can detect a 0.2 gallon per hour leak rate or a release of 150 gallons within 30 days with probability of detection and probability of false alarm in accordance with R18-12-240(A)(4);

b. The owner and operator can demonstrate that the method is able to detect a release as effectively as any of the methods allowed in subsections (C) through (H). 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 shall comply with any conditions imposed by the Department on its use to ensure the protection of human health and the environment.

Notes

Ariz. Admin. Code § R18-12-243

Adopted effective July 30, 1996 (Supp. 96-3). Amended by final rulemaking at 25 A.A.R. 3123, effective 1/1/2020.