The testing of an underground storage tank (UST) should be a straightforward process. The tank test company sends a technician certified by the manufacturer and state they are operating in. The heating system or emergency generators that are connected to the tank are taken offline temporarily. The manways are removed and the fuel system supply, return and vent lines are closed off or plugged. Groundwater monitoring wells are checked for water table height and pretest calculations are made. The tank testing equipment is inserted in the tank fill pipe or test point and the test process is started. Unfortunately, a tank testing service rarely happens as we just described and this impacts the time to test, cost of testing and the duration that the facilities equipment is offline.
Planning Ahead for Tank Tightness Testing
If your facility has an underground storage tank and testing is required then it’s a good practice to have your tank inspected prior to scheduling the test. Why is this important? Many USTs were not installed with testing in mind and changes to the configuration are often necessary. The following are common things to check for on your UST prior to scheduling a test:
- Groundwater monitoring well within 25 feet of the UST
- Fill pipe diameter greater than 2 inches
- Fill or test piping free of corrosion
- Vent pipe accessible from rooftop or less than 16’ high
- UST easily isolated from piping (tank with shutoffs or unions are ideal)
- Manifolded USTs able to be disconnected and tested separately
- UST access (USTs that are elevated or below grade can be difficult to reach with test equipment)
- UST sumps accessible (tight spacing limits the use of wrenches if piping needs to be disconnected to add test plugs)
Sometimes the tank is blocked by temporary structures, especially if located in a parking lot. Roll-off containers or trash compactors are often installed near underground tank pads and can cover tank manways. Vehicle access to facility loading docks, hospital entrances and marine boat ramps are a few examples of high traffic areas. Traffic restrictions should be in place prior to performing a tank test.
Underground Storage Tank Testing Companies
The manufacturer of tank testing equipment provides training and certification for its equipment and test method. The test methods are evaluated by the National Work Group on Leak Detection Evaluations (NWGLDE) and certified by a 3rd party to meet EPA leak detection performance requirements. The technician performing the tightness testing must be trained and certified for the equipment they use and include their certification number on the tank test report. The State of NH also requires the technician to have an International Code Council (ICC) Certification for UST Tank Tightness Testing. A list of certified tank testing companies can be found on the NH UST Program Resources Page.
EPA Requirements for Tank Testing
The requirement for testing is typically covered by Automatic Tank Gauges (ATGs) installed at regulated facilities. These gauges use the ‘Continuous In-Tank Leak Detection Method’ which meets EPA leak detection requirements. If the monitoring equipment has failed or is in an alarm condition then the state or local fire department can require a tightness test. Real estate transactions may also trigger testing. The buyer may need a written statement for the bank or insurance company that proves the UST is sound.
Consumptive Use tanks (tanks that supply fuel to heating systems or gas to fleet vehicles) larger than 1,100-gallons, do not have the same leak detection requirements as regulated tanks. An interstitial monitor that is capable of detecting leaks from the inner wall to the outer wall meets the leak detection requirement for Consumptive Use tanks.
Underground storage tanks connected to emergency generators and fire pumps, larger than 1,000-gallons and installed prior to January 2, 2015, that do not have ATGs, are required to have annual tightness tests performed. Owners of USTs, smaller than 1,000-gallons, can utilize weekly tank gauging per CMR 80.26(7) as it satisfies the leak detection requirements or perform monthly gauging and annual tightness testing.
Tank Testing Nightmares
During the 14-years that we have conducted tank tests, there have been a number of tough jobs that we apply the label “nightmare” too. The following are examples of problem jobs and images of properly installed tanks to highlight the difference between a poor installation and good one as it applies to tank testing.
Figure 1: Spill Container with Two 45 Degree Elbows
Figure 2: Ideal Test Point Configuration
The UST in Figure 1 had three elbows coming off the 4” riser pipe which connect to an aboveground spill bucket. This configuration is a “nightmare” for tank testers because there is no direct access to the tank. A tester is not able to measure the fuel and water levels, or the diameter of the tank, which is critical information for testing an underground tank. Also, technicians need a direct access point to install their volumetric and non-volumetric instruments. Figure 2 is an example of an ideal test point. The fill pipe is 4” diameter and is piped straight to the top of the UST.
Figure 3: Overfill Prevention Valve Rusted in Place
Figure 4: An example of a functioning drop valve
Figure 3 is an example of galvanic corrosion. The fill pipe is so corroded that the aluminum drop tube has bonded to the steel riser pipe. Test instruments cannot be inserted into the fill pipe if a rusted part like this drop tube is blocking access. Figure 4 shows a drop tube inside a riser pipe of well-maintained UST.
Figure 5: Three Feet of Water in UST Sump
Figure 6: Sealed Fiberglass Containment Sump with Good Drainage
UST sumps are designed to contain piping leaks but they will hold 50 to 100-gallons of water if left exposed to the elements. Nothing slows down a tank tightness test like submerged pipes and fittings. The water accumulation in Figure 5 can be avoided by installing a manway larger than the diameter of the sump and installing a covered sump. Figure 6 shows an ideal sump and manway installation. The containment sump is inside this 36” manway. A compression lid will cover the piping so any water that enters the manway will pass into the crushed stone around the sump.
Figure 7: Interstitial Sensor Port Filled with Wet Soil
Figure 8: An example of a clean, dry test point
The interstitial space test point in Figure 7 is filled with soil. Tank testers aren’t usually equipped with tools for removing soil in tank sumps. The tank owner should check this manway on monthly walk-through inspections and clear any debris buildup. Figure 8 shows a clean, dry test point. It not only provides easy access to the interstitial test point but will reduce corrosion and prevent soil and water from entering the piping.
Figure 9: Vent Outside 2nd Floor School Window
Figure 10: Vent Pipe Located Above Roof Line
The vent pipe in Figure 9 is mounted in a location that is inaccessible for tank testing. It is also not installed to code despite it being a school building. The vent is mounted too close (must be at least 24 inches away) to a window which will allow fuel vapors to be drawn inside. The building in Figure 10 shows an underground tank vent pipe properly mounted above the roof line. This location is safe and provides roof top access to the vent so it can be plugged for testing.
Common Causes of Tank Testing Failures
Underground storage tanks are not usually the source of a leak detected during a tank tightness test. It’s typically a fitting connected to the tank that fails. Here is a listing of tank failure points starting from most to least common:
- Fill Pipe – Fill pipes are the most actively used fitting on an underground tank. Vibration during delivery of fuel is the primary reason for this pipe loosening.
- Spill Buckets – Ground water regularly entering a spill bucket will result in rust and corrosion developing at the riser pipe attachment.
- Vent Pipes – a vent pipe can become loose just below grade, or above grade joints may dry out, depending on the location of the tank and the support structure for the pipe.
- Tank Manways – Leaks found at manways usually occur if the sump protecting the manway is not water tight. The rubber seals will dry out over time and need to be replaced. A manway leak is usually confirmed by injecting helium in the tank and tracing the leak with a helium sensor.
- Level Gauges – These gauges will allow air in through the gauge pump so they must be disconnected and the line plugged.
- Level Sensor Mount Points – USTs that have Automatic Tank Gauges use electronic level sensor to measure the fuel level. These need to be removed prior to testing because the seals aren’t always air tight.
- Fuel Supply and Return Lines – It is rare to have a leaking supply or return line but small leaks do occur in the threaded fittings in UST sumps. Typically a visual inspection will catch this leak prior to testing.
- Check Valves – Check valves prevent siphoning and are used to keep a fuel pump primed. Check valves can wear over time and allow air to pass through the valve. Isolating USTs by disconnecting and plugging supply and return lines removes check valves from the test.
Reporting Tank Tightness Test Failures
In Massachusetts the owner/operator and fire depart must be notified within 24 hours of a UST or piping that fails a tightness test. Any piping that has failed must be isolated and emptied immediately. A failing UST must be emptied within 72 hours of a failed tightness test. Once the tank or piping is repaired it must be tested within 30 days.
New Hampshire requires notification of the Department of Environmental Services (DES) within 24 hours after a test failure. The tank owner must investigate the cause of the leak within 7 days or temporarily close the system within 7 days and permanently close with within 30 days.
Declaring a Tank “Tight”
An underground tank system is declared tight when testing is performed in accordance with the EPA “Standard Test Procedure for Evaluating Leak Detection” and is capable of detecting a leak of 0.1 gallon/hour with a probability of detection of no less than 95%. After January 1, 2018 the testing systems are required to have a detectable leak rate of .05 with a probability of detection of no less than 95%. Equipment manufacturers must show their leak detection methods meet these performance requirements. Ask the underground tank test company that performs your test for a copy of the evaluation results to keep on file with your report. This will satisfy the EPA’s record keeping requirement.
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