WAC 173-360-345   Methods of release detection for tanks.  (1) Any method of release detection for tanks shall meet the performance requirements of this section. In addition, methods used after December 22, 1990, except for methods permanently installed prior to that date, shall be capable of detecting the leak rate or quantity specified for that method in subsection (6)(b), (c), (d), and (e) of this section with a probability of detection of 0.95 and a probability of false alarm of 0.05. (That is, under test conditions, a method will correctly detect at least ninety-five of one hundred actual releases, and will falsely indicate a release no more than five times in one hundred tests of nonleaking systems.)

Note:

The establishment of leak indication thresholds is a means of setting a standard for the equipment or method used. It is not in any way meant to imply that actual leak rates less than these limits are allowable. No release is acceptable, and any indication that a release may have occurred should be investigated in accordance with WAC 173-360-360. Manufacturers and certified UST supervisors installing or utilizing leak detection equipment and/or methods must follow EPA's standard test procedures for evaluating leak detection methods to demonstrate compliance with the requirements of subsection (1) of this section.

     (2) UST systems that meet the new tank or upgraded tank performance standards in WAC 173-360-305 or 173-360-310, and the inventory control requirements in subsection (6)(a) or (b) of this section, may use tank tightness testing (conducted in accordance with subsection (6)(d) of this section) at least every five years until December 22, 1998, or until ten years after the tank is installed or upgraded under WAC 173-360-310(2), whichever is later.

     (3) UST systems that do not meet the new tank or upgraded tank performance standards in WAC 173-360-305 or 173-360-310 may use inventory controls (conducted in accordance with subsection (6)(a) or (b) of this section) and annual tank tightness testing (conducted in accordance with subsection (6)(d) of this section) until December 22, 1998, when the tank shall be upgraded under WAC 173-360-310 or permanently closed under WAC 173-360-385.

     (4) Tanks with capacity of one thousand gallons or less may use weekly tank gauging conducted in accordance with subsection (6)(b) of this section.

     (5) Tanks that store fuel solely for use by emergency power generators may use the following methods of release detection:

     (a) Emergency power generator tanks with nominal capacity of one thousand gallons or less may use monthly tank gauging conducted in accordance with subsection (6)(c) of this section.

     (b) Emergency power generator tanks with nominal capacity of one thousand one to two thousand gallons may use monthly tank gauging conducted in accordance with subsection (6)(c) of this section, in conjunction with annual tank tightness testing conducted in accordance with subsection (6)(d) of this section.

     (c) Except as provided in subsection (2) of this section, emergency power generator tanks with nominal capacity greater than two thousand gallons may use weekly tank gauging conducted in accordance with subsection (6)(b) of this section, in conjunction with annual tank tightness testing conducted in accordance with subsection (6)(d) of this section.

     (6) Each method of release detection for tanks used to meet the requirements of WAC 173-360-335 shall be conducted in accordance with the following:

     (a) Daily inventory control. Daily inventory control (or another test of equivalent performance) shall be conducted in a manner capable of detecting a release of at least 1.0 percent of flow-through plus 130 gallons on a monthly basis in the following manner:

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

     (ii) The equipment used is capable of measuring the level of regulated substance in the tank over the full range of the tank's height to the nearest one-eighth of an inch;

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

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

     (v) Dispensing of regulated substances is metered and recorded within the local standards for meter calibration or an accuracy of at least six cubic inches for every five gallons of regulated substances which is withdrawn; and

     (vi) The measurement of any water level in the bottom of the tank is made to the nearest one-eighth of an inch at least once a month.

Note:

Practices described in the American Petroleum Institute Publication 1621, "Recommended Practice for Bulk Liquid Stock Control at Retail Outlets," may be used, where applicable, as guidance in meeting the requirements of this paragraph.

     (b) Weekly tank gauging. Only tanks of one thousand gallons or less nominal capacity may use weekly tank gauging as the sole method of release detection. Tanks of one thousand one to two thousand gallons may use the method in place of daily inventory control in (a) of this subsection, in conjunction with tank tightness testing, as specified in (d) of this subsection. Tanks of greater than two thousand gallons nominal capacity may use this method to meet the requirements of WAC 173-360-330 through 173-360-355 only if such tanks store fuel solely for use by emergency power generators. Weekly tank gauging shall meet the following requirements:

     (i) Tank liquid level measurements are taken weekly at the beginning and ending of a period of at least thirty-six hours during which no liquid is added to or removed from the tank;

     (ii) Level measurements are based on an average of two consecutive stick readings at both the beginning and ending of the period (that is, four measurements shall be taken, two consecutive measurements at the beginning and two consecutive measurements at the end of the period during which no liquid has been added or removed from the tank);

     (iii) The equipment used is capable of measuring the level of regulated substance in the tank over the full range of the tank's height to the nearest one-eighth of an inch;

     (iv) If the variation between beginning and ending measurements exceeds the weekly or monthly standards in the following table, a leak may be occurring and the requirements of WAC 173-360-360 through 173-360-375 shall be followed:

Nominal Tank Capacity	Weekly Standard (one test)	Monthly Standard
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
2,001 gallons or more*	.75% of capacity	.5% of capacity
(*Emergency Power Generator Tanks only.)

     (c) Monthly tank gauging. Only tanks that store fuel solely for use by emergency power generators with a nominal capacity of two thousand gallons or less may use monthly tank gauging as a method of release detection. Such tanks with nominal capacity of one thousand one to two thousand gallons may use manual tank gauging in conjunction with tank tightness testing conducted in accordance with this section. Monthly tank gauging shall meet the following requirements:

     (i) Inventory volume measurements for regulated substance inputs, withdrawals, and the amount still remaining in the tank are recorded whenever inputs or withdrawals occur;

     (ii) Tank liquid level measurements reconciled with inventory volume measurements are taken monthly at the beginning and ending of a period of at least twenty-one days, except when extreme snowfall or other travel obstructions occurring in remote locations and preventing access are specifically documented by the owner and operator;

     (iii) Level measurements are based on an average of two consecutive readings at both the beginning and ending of the period (that is, four measurements shall be taken, two consecutive measurements at the beginning and two consecutive measurements at the end of the period);

     (iv) The equipment used is capable of measuring the level of regulated substance in the tank over the full range of the tank's height to the nearest one-eighth of an inch or a corresponding amount of gallons;

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

     (vi) If the variation between beginning and ending measurements exceeds the monthly standards in the following table, a leak may be occurring and the requirements of WAC 173-360-360 through 173-360-375 shall be followed:

Nominal Tank Capacity	Monthly Standard
550 gallons or less	5 gallons
551-1,000 gallons	7 gallons
1,001-2000 gallons	13 gallons

     (d) Tank tightness testing. Tank tightness testing (or another test of equivalent performance) shall be capable of detecting at least a 0.1 gallon per hour leak rate from any portion of the tank up to the ninety-five percent full level or up to the product level limited by an overfill prevention device 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. Tank tightness testing shall be conducted and the results reported in accordance with the instructions for that method.

     (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:

     (i) The automatic product level monitor test can detect at least a 0.2 gallon per hour leak rate from any portion of the tank that routinely contains a regulated substance;

     (ii) Daily inventory control (or another test of equivalent performance) is conducted in accordance with the requirements of (a) of this subsection; and

     (iii) Automatic tank gauging equipment must be operated in the test mode at least once per year, and the results kept on file.

     (f) Vapor monitoring. Testing or monitoring for vapors within the soil gas of the excavation zone shall meet the following requirements:

     (i) 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 zone;

     (ii) The stored regulated substance, or a tracer compound placed in the tank 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 tank;

     (iii) 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 thirty days;

     (iv) The level of background contamination in the excavation zone will not interfere with the method used to detect releases from the tank;

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

     (vi) In the UST excavation zone, the site is evaluated for its appropriateness for installation of vapor monitors to ensure compliance with the requirements of this subsection and to establish the number and positioning of monitoring wells that will detect releases within the excavation zone from any portion of the tank that routinely contains a regulated substance; and

     (vii) Monitoring wells are clearly marked and secured to avoid unauthorized access and tampering.

Note:

Monitoring wells must also comply with the minimum standards for construction, maintenance, and abandonment of resource protection wells specified in chapter 173-160 WAC. UST system owners and operators are encouraged to retain the services of a qualified professional who is experienced in determining the design and placement of vapor monitoring wells surrounding an UST system.

     (g) Groundwater monitoring. Testing or monitoring for liquids on or in the groundwater shall meet the following requirements:

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

     (ii) Groundwater is never more than twenty 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);

     (iii) 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;

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

     (v) Monitoring wells or devices intercept the excavation zone or are as close to it as is technically feasible;

     (vi) 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;

     (vii) Within and immediately below the UST system excavation zone, the site is evaluated for its appropriateness for installation of groundwater monitors to ensure compliance with the requirements in (g)(i) through (v) of this subsection 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; and

     (viii) Monitoring wells are clearly marked and secured to avoid unauthorized access and tampering.

Note:

Monitoring wells must also comply with the minimum standards for construction, maintenance, and abandonment of wells specified in chapter 173-160 WAC. UST system owners and operators are encouraged to retain the services of a qualified professional who is experienced in determining the design and placement of groundwater monitoring wells surrounding an UST system.

     (h) 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 tank that routinely contains a regulated substance and also meets one of the following requirements:

     (i) 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;

Note:

The provisions outlined in the Steel Tank Institute's "Standard for Dual Wall Underground Storage Tanks" may be used as guidance for aspects of the design and construction of underground steel double-walled tanks.

     (ii) 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;

     (A) 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 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 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 thirty days;

     (E) The site is evaluated for its appropriateness for installation of interstitial monitors to ensure that the secondary barrier is always above the groundwater and not in a twenty-five-year flood plain, unless the barrier and monitoring designs are for use under such conditions; and

     (F) Monitoring wells are clearly marked and secured to avoid unauthorized access and tampering.

     (iii) 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) Statistical inventory reconciliation. Statistical inventory reconciliation (SIR) shall meet the following requirements:

     (i) Statistical inventory reconciliation must detect at least a 0.2 gallon per hour leak rate from any portion of the tank that routinely contains a regulated substance with a probability of detection of at least 0.95 and a probability of false alarm of no more than 0.05; and

     (ii) Daily inventory control must be performed in accordance with the requirements of (a) of this subsection; and

     (iii) Owners and operators must submit daily inventory records from at least the previous thirty days on a monthly basis to a SIR vendor whose statistical analysis method has been demonstrated to meet the performance standard of (i) of this subsection; and

     (iv) The SIR vendor must perform an independent SIR analysis on the daily inventory records submitted and report the results to the owner or operator within fifteen days of receiving them; and

     (v) If the results of a SIR analysis show a 0.2 gallon per hour or greater leak rate in any single month, from any portion of the tank that routinely contains a regulated substance with a probability of detection of at least 0.95 and a probability of false alarm of no more than 0.05, it shall be determined to be a "fail." If an owner or operator receives a "fail" for two consecutive months, the owner or operator shall have a tank tightness test conducted in accordance with (d) of this subsection within fifteen days of receiving the second "fail" from the SIR vendor.

     (j) Other methods. Any other type of release detection method, or combination of methods, can be used if:

     (i) It can detect a 0.2 gallon per hour leak rate or a release of one hundred fifty gallons within a month with a probability of detection of 0.95 and a probability of false alarm of 0.05; or

     (ii) The department or delegated agency may approve another method if the owner and operator can demonstrate that the method can detect a release as effectively as any of the methods allowed in (d) through (i) of this subsection. In comparing methods, the department or delegated agency 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 or delegated agency on its use to ensure the protection of human health and the environment.



[Statutory Authority: Chapter 90.76 RCW. 95-04-102, § 173-360-345, filed 2/1/95, effective 3/4/95; 91-22-020 (Order 91-26), § 173-360-345, filed 10/29/91, effective 11/29/91; 90-24-017, § 173-360-345, filed 11/28/90, effective 12/29/90.]