UST Services, Inc.
Precision Underground Leak Detection Specialists
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Stage II Testing

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Introduction:

Stage II Systems are required at nearly all fueling facilities located in areas identified as "non-attainment areas" by the U.S. Environmental Protection Agency (EPA). The purpose of a Stage II system is to prevent gasoline vapor emissions from releasing into the air. Stage II systems collect vapors from vehicle gasoline tanks as they are fueling and return them to the fueling facility tanks, thereby reducing the emissions into the air.  In Texas, the "non-attainment areas" are the Dallas-Fort Worth Area, Beaumont Port Arthur Area and the Houston-Galveston area.

The Texas Commission on Environmental Quality (TCEQ) follows the rules and regulations that were enacted by the California Air Board (CARB). The Executive Orders issued by CARB include installation, operating and testing procedures for all approved Stage II systems. 

In general, there are two types of systems, the balanced system and the vapor assist system. 

Testing Requirements

All gasoline tanks at a location with Stage II installed need to be manifolded together to allow equalization so that none of the tanks are either over or under pressurized during normal operation. 

This test involves introducing nitrogen gas into the system from a port in one of the dispensers at the location and determining whether all of the gasoline tanks are properly manifolded either underground or above ground. After introducing nitrogen gas into the dispenser port, all of the gasoline tanks connected to the vapor recovery system are pressurized. The system passes this test if all of the gasoline tanks are pressurized after introducing the nitrogen. If a tank is not pressurized, it can be established that the tank is not included in the manifold. 

The Dynamic Backpressure Test involves the testing of vapor return lines from the dispenser to the tanks and the testing of the vent lines from the vents to the tanks. 

By design, the return line and vent line piping must be sloped back to the tank so that liquids that collect in them drain back to the tank. The purpose of the test is to insure that there is no appreciable blockage in either the Stage II return line or the vent line.

Blockage in the Stage II return line can cause the Stage II system not to operate because the flow of vapors from a fueling vehicle can not be returned to the fuel system.

Blockage in the vent line can cause the tank to pressurize above the maximum pressure rating of the tank which can cause the tank to rupture.

Stage II fuel systems are designed to contain the vapors that are collected from the fueling of vehicles. Recent research from the California Air Board indicates that emissions from fueling locations is a major cause of ozone creation. 

The Pressure Decay Test  is designed to assure that the system is sealed to the manufacturers specifications. This test must be performed annually as well as part of the initial test and the 3 year full system test. 

The testing procedure involves introducing nitrogen into the tank system to a predetermined pressure and measuring the change in pressure over a 5 minute period. If the system decays beyond a predetermined specification, the leak in the system must be located and repaired. 

The most common causes of leaks are defective nozzles or hoses, Stage I adapters, vent caps, fill caps and fill adapters and the related gasketing. Most of these parts can be replaced as part of the testing procedure. 

In order for a Stage II system to properly remove vapors from the vehicle fuel tank during fueling, many Stage II system administrative orders require that the dispensers dispense at least 6 gallons per minute and less than 10 gallons per minute. This test is performed before vapor or air over liquid tests (V/L or A/L) nozzle tests are performed.

Five gallons of gasoline for each product is pumped from the dispenser located closest to the tanks. The time to dispense the five gallons is recorded with a stopwatch. If the required threshold is met, then testing progresses to the V/L or A/L  test discussed below. 

After establishing that the dispensers are pumping fuel at a rate within the parameters specified in the executive order, nozzle tests are performed to confirm that the vapor motors are pulling back vapors from the vehicle tank at a rate within the parameters specified in the executive order. This test is generally the last test that is performed at the site.  

Annual Testing Requirements: In the years between the initial test and the 3 year tests, There are lesser testing requirements.

The pressure decay test is required annually on all systems. As stated above it it part of the Initial and 3 year testing requirements and is also part of the annual testing that is required. 

The nozzle tests are required on most of the vapor assist systems. Balance systems do not have an annual nozzle test requirement. 

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Last modified: October 21, 2006