Petroleum USTs with a capacity of more than 2,000 gallons shall be monitored at least every thirty (30) days for releases using one or more of the following methods:
(a) Inventory control. Inventory control is never acceptable as a leak detection method except when it is combined with another method. Product inventory control (or another test of equivalent performance) shall be conducted monthly to detect a release of at least 1.0 percent (1%) of throughput plus one hundred thirty (130) gallons in the following manner: - (i) Inventory volume measurements for regulated substance inputs, withdrawals, and the amount still remaining in the UST shall be recorded each operating day;
- (ii) The equipment used shall be capable of measuring the depth of regulated substance over the full range of the USTs height to the nearest one-eighth (1/8) of an inch;
- (iii) The regulated substance inputs shall be reconciled with delivery receipts by measurement of the UST inventory volume before and after delivery;
- (iv) Deliveries shall be made through a drop tube that extends to within six (6) inches of the Storage Tank bottom;
- (v) Dispensing of regulated substances shall be metered and recorded within the local standards for meter calibration or an accuracy of six (6) cubic inches for every five (5) gallons of regulated substance withdrawn; and
- (vi) Water in the bottom of the UST shall be measured to the nearest one-eighth (1/8) of an inch at least once a month.
- (vii) Owners and/or operators using inventory control may combine this method with tank tightness testing at least every five (5) years until December 22, 2008, or until ten (10) years after the UST itself first met the requirements of Section 6(a), whichever is sooner;
- (viii) Owners and/or operators using inventory control shall report a suspected release under Section 19(c) of this chapter whenever:
- (A) The inventory control fails to balance within 1.0 percent (1%) of total throughput plus one hundred thirty (130) gallons for the second consecutive month;
- (B) More than 20 daily readings are either positive or negative for the second consecutive month; or
- (C) A graph of the daily over/short readings shows a consistent non-zero trend for two (2) consecutive months.
- (ix) The following methods are methods of equivalent performance to inventory control:
- (A) Vapor Monitoring conducted in accordance with section 16(d) of this chapter;
- (B) Groundwater Monitoring conducted in accordance with section 16(e) of this chapter;
- (C) Interstitial Monitoring conducted in accordance with Section 16(f) of this chapter;
- (D) Statistical Inventory Reconciliation conducted in accordance with Section 16(g) of this chapter;
- (E) Tracer Surveys conducted in accordance with Section 16(h) of this chapter;
- (F) Passive Acoustical Sensing conducted in accordance with Section 16(k) of this chapter; and
- (G) Other methods approved under Section 16(j) of this chapter, providing that the approval of the method specifically states that the method is of equivalent performance to inventory control.
(b) Tank tightness testing. Tank tightness testing shall be capable of detecting a 0.1 gallon per hour leak rate from any portion of the UST that routinely contains 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 facility of the water table. Whenever a tank tightness test shows a failing result, the owner and/or operator shall report a suspected release and follow Section 20(a)(i) and (ii) of this chapter.
(c) Automatic tank gauging (ATG). Equipment for automatic tank gauging that tests for the loss of a regulated substance shall detect a 0.2 gallon per hour leak rate from any portion of the tank that routinely contains a regulated substance. Owners and/or operators using automatic tank gauging shall also: - (i) conduct inventory control in conformance with paragraph (a) of this section, unless:
- (A) the regulated substance is placed in the UST in batches of twenty-five (25) gallons or less;
- (B) the tank is used only to fuel an emergency power generator;
- (C) a passing result is obtained monthly from the Automatic Tank Gauge with the tank at least 85% full;
- (D) the automatic tank gauge itself reconciles the inventory to the same levels as required by paragraph (a)(i) of this section; or
- (E) a method of equivalent performance to inventory control is also used.
- (ii) report a suspected release and follow the requirements of Section 19(c) of this chapter whenever:
- (A) Any calendar month goes by when a passing result cannot be obtained from the ATG sometime during the month; or
- (B) A pattern becomes evident that the ATG produces a failing result whenever the level of a regulated substance in the tank is high, even if passing results can be obtained when the level is low.
- (C) Inventory control fails for the second consecutive month.
(d) 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 UST system, is sufficiently volatile 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 (30) days;
- (iv) The soil and backfill material immediately surrounding the UST system shall not be contaminated with the regulated product in such a way as to interfere with the method used to detect releases from the UST system;
- (v) The vapor monitors shall be designed and operated 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;
- (vi) In the UST excavation zone , the site is assessed to ensure compliance with the requirements in this section and to establish the number and positioning of vapor monitoring wells that will detect releases within the excavation from any portion of the tank that routinely contains regulated substance; and
- (vii) Vapor monitoring wells shall be clearly marked for identification and secured to avoid unauthorized access and tampering.
- (viii) Owners and/or operators using vapor monitoring wells for leak detection shall report a suspected release under Section 19(c) of this chapter whenever a vapor monitoring device detects a leak and cannot be made to reset within forty-eight (48) hours.
- (ix) After the effective date of these regulations, no new UST facility shall be installed using vapor monitoring as the only leak detection method. Owners and/or operators may install vapor monitoring wells as a secondary method. In the event that vapor monitoring wells are installed in the backfill, a permit to construct under Chapter 3, Wyoming Water Quality Rules and Regulations is not required.
(e) Groundwater monitoring. Testing or monitoring for liquids on 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 (1);
- (ii) Groundwater is never more than twenty (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);
- (iii) The slotted portion of the monitoring well casing or well screen 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 groundwater conditions;
- (iv) Monitoring wells shall be sealed from the ground surface to the top of the filter pack with hydrated bentonite and concrete;
- (v) Monitoring wells or devices shall intercept the excavation zone or are as close to it as is technically feasible;
- (vi) The continuous monitoring devices or manual methods used shall be capable of detecting the presence of at least one-eighth (1/8) of an inch of free product on top of the groundwater in the monitoring wells;
- (vii) Within and immediately below the UST excavation zone, the site shall be assessed to ensure compliance with the requirements in Section 16(e)(i) through (v) 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 a regulated substance;
- (viii) Monitoring wells shall be clearly marked for identification and secured to avoid unauthorized access and tampering; and
- (ix) Groundwater monitoring shall not be used when the ambient groundwater is already contaminated with the regulated substance being stored in the UST system.
- (x) Owners and/or operators using groundwater monitoring shall report a suspected release and follow the requirements of Section 19(c) and (d) of this chapter whenever any regulated substance is observed in any monitor well at any level whatsoever.
- (xi) After the effective date of these regulations, no new UST facility shall be installed using groundwater monitoring as the only leak detection method. Owners and/or operators may install groundwater monitoring wells as a secondary method. In the event that groundwater monitoring wells are installed in the backfill, a permit to construct under Chapter 3, Wyoming Water Quality Rules and Regulations is not required.
(f) 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 shall be capable of detecting a release through the inner wall in any portion of the tank that routinely contains a regulated substance;
- (ii) For UST systems with a secondary barrier within the excavation zone, the sampling or testing method used shall be capable of detecting a release between the UST system and the secondary barrier;
- (A) The secondary barrier around or beneath the UST system shall consist of artificially constructed material that is sufficiently thick and impermeable to direct a release to the monitoring point and permit its detection. The permeability of this barrier to the regulated substance stored shall be no more than 10-6 cm/sec;
- (B) The barrier shall be 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 USTs, the secondary barrier shall be installed so that it does not interfere with the proper operation of the CP system;
- (D) Groundwater, soil moisture, or rainfall shall not render the testing or sampling method used inoperative so that a release could go undetected for more than thirty (30) days;
- (E) The site shall be 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; and
- (F) Monitoring wells shall be clearly marked for identification and secured to avoid unauthorized access and tampering.
- (iii) For USTs with internally fitted liners, an automated device shall be capable of detecting a release between the inner wall of the UST and the liner. The liner shall also be compatible with the regulated substance stored.
- (iv) Owners and/or operators using interstitial monitoring shall report a suspected release and follow the requirements of Section 19(c) of this chapter whenever any monitoring device indicates a leak and the device itself cannot be shown to be defective within forty-eight (48) hours of the initial alarm.
(g) Statistical Inventory Reconciliation (SIR). All SIR methods shall: - (i) meet the requirements found in Section 16(a) for inventory control
- (ii) be capable of detecting a 0.2 gallon per hour leak rate or a release of one hundred fifty (150) gallons within a month with a probability of detection of at least 0.95 and a probability of false alarm of no more than 0.05; and
- (iii) be approved, in writing, by the department prior to use.
- (iv) All "inconclusive" results shall be investigated by the owner and/or operator as soon as they are reported by the SIR company, including a complete audit of all input data. The owner and/or operator shall make every effort to resolve all "inconclusive" results as soon as they are reported. If the inventory for an entire month fails to balance within two thousand (2,000) gallons, that month shall be treated as inconclusive. A month with an un-resolved inconclusive result is a month when no valid leak detection was provided.
- (v) Owners and/or operators using SIR shall report a suspected release and follow the requirements of Section 19(c) of this chapter whenever:
- (A) Any single month is reported as a failure for the UST system by the SIR company;
- (B) Any month is reported by the SIR company as "inconclusive" unless that inconclusive result has been resolved by re-submission of audited inventory numbers to the SIR company.
- (vi) UST Systems with a throughput of more than 500,000 gallons per month in any single system shall not be monitored using SIR as the only release detection method.
(h) Tracer Surveys. Owners and/or operators may use tracer surveys as an approved monthly monitoring technique if: - (i) The tracer method can detect a 0.2 gallon per hour leak rate or a release of one hundred fifty (150) gallons within a month with a probability of detection of 0.95 and a probability of false alarm of 0.05; and
- (ii) The tanks are inoculated with the same tracer each month;
- (iii) The tanks are inoculated each month before the 10th day of the month;
- (iv) The Tracer Survey is completed before the 25th day of each month;
- (v) The report for each month includes the calculations of the amount of tracer needed, the amount actually added to each tank, and the calculated leak detection limit in gallons per day; and
- (vi) The report for each test clearly states that the tank(s) either passed or failed the test.
- (vii) Any failing test using tracer surveys shall be treated as a suspected release under Section 24 or 25.
(i) Passive Acoustic Sensing. Owners and/or operators of Storage Tanks using this method shall be equipped with a continuous sensing system capable of detecting a release of 0.2 gallons per hour or a release of 150 gallons per month with a probability of detection of 0.95 and a probability of false alarm of 0.05. All passive acoustic sensing systems shall produce a written record showing that the system is on and operable. All passive acoustic sensing systems shall be calibrated annually;
(j) Other technology. With prior department authorization, pursuant to Section 33, other types of release detection methods, or combination of methods, may be used if: - (i) The method can detect a 0.2 gallon per hour leak rate or a release of one hundred fifty (150) gallons within a month with a probability of detection of 0.95 and a probability of false alarm of 0.05; or
- (ii) The owner and/or operator can demonstrate that the method can detect a release as effectively as any of the methods allowed in Section 16(b) 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/or operator shall comply with any conditions imposed by the department to ensure the protection of human health and the environment.
(k) Multiple Methods. Whenever these regulations require the use of more than one leak detection method, the owners and/or operators shall meet all of the requirements for all of the leak detection methods required.
020-17 Wyo. Code R. § 17-16