Common causes of UST leaks

causes of underground storage tank leaks We are often asked for information on the source of leaks from underground storage tanks (USTs). It is important to address these inquiries because UST leaks may not only cause environmental damage and be very costly to clean up, but can also be very harmful to human health. For this article we went back through our files from over 300 leaking underground storage tank (LUST) projects to find the top 10 causes of underground storage tank leaks.

The leaking UST sites ranged from new service stations with modern double-walled, fiberglass tanks and lines with spill protection devices to old, abandoned, single-walled steel tanks and lines with no spill protection devices.

The sources of the leaks were relatively easy to identify at sites less than 25 years old because of accurate record keeping and government reporting requirements.

Leak sources at sites greater than 25 years old were often determined forensically by the presence of soil staining and contamination.

In many cases it was difficult to pinpoint the exact source of the contamination and sometimes there were indications of multiple leaks that had occurred over many years.

causes of underground storage tank leaks — New product line and tank installation

1. Steel product lines and fittings

Product lines are the steel pipes that convey fluids from the underground tank to the dispenser. Steel is subject to corrosion.

During tank removal projects we often observed soil staining that indicated past leaks, predominantly near fittings.

Modern product lines are constructed of double-walled fiberglass and the interstice is electronically monitored for leaks. There are also leak detectors which monitor fluid pressure and will shut down the flow of product in the event of a line leak.

2. Tank overfills

Overfills occur when a tanker truck delivers product to the underground storage tank. The fill ports for older steel tanks merely consisted of a pipe sticking up out of the ground.

The tanker truck operator connected a hose to the fill pipe to transfer the product from the truck to the tank. If the tank became full, there was a shutoff device to stop the flow of product; however, it was not unusual for some overflow product to spill into the ground around the fill port when the hose was disconnected.

Over the lifespan of the tanks, these small leaks added up to significant spills. Modern fill ports are inserted though spill buckets. In the event of a small spill around the fill port, product is captured in the bucket. There is a chain on the bucket for the operator to open a valve to drain the overfilled fluid back into the UST.

3. Leaks from dispensers

Dispensers have many fittings, filters and hose connections. Older dispensers were installed above native soil and any drips or leaks spilled onto the ground. This is another case where small leaks accumulated over time.

Modern dispensers are constructed over spill containment boxes that are designed to capture any spills or drips.

4. Steel tanks

Prior to 1980, USTs were predominantly constructed of steel. Depending upon soil conditions, some tanks lasted many decades without any corrosion, while at other sites corrosion was present within 10 years.

Newer tanks employed cathodic protection systems to prevent oxidation (rust) which often worked quite well.

5. STP sumps

Submersible transfer pumps are used to pump the product out of the tank to the dispensers. Fittings for these pumps rest on top of the tanks and a sump or manhole is constructed around the pump so it may be accessed for servicing.

Significant spills have resulted from high pressure leaks at the top of the pumps or pump fittings. On older installations, leaks spilled over the sides of the tanks and into the ground. Modern STP sumps are constructed inside spill protection devices designed to contain leaks.

6. Fuel delivery errors

Fuel delivery errors have occurred due to failure of shutoff valves, fuel dispensed into something other than the proper fuel port, insecure hose connections, etc.

7. Leaking overfill and dispenser protection devices

Modern overfill and spill protection and detection devices work very well. However, seals in these devices can become dried out and cracked over time. The high concentration of ethanol in modern gasoline can also cause the seals to become brittle and fail.

8. Leaking fiberglass product lines and tanks

Modern fiberglass tanks and lines are double-walled and employ interstitial monitoring devices to detect leaks.

Most leaks occur due to incorrectly constructed fittings or due to improper installation which allowed the fiberglass to flex and crack.

9. Customer errors

Customer errors include errors such as driving off with the dispenser hose connected to the vehicle, crashing into dispensers, and unattended fueling resulting in overfilling of their vehicles.

Dispensers contain shear valves designed to shut off the flow of fuel in the event of a catastrophic failure, but they do not work in every circumstance.

10. Other leak causes

Other causes include inadvertent instances such as drilling through tanks or lines during construction or environmental investigations and errors made during maintenance. Leaks have also been caused purposely by individuals with criminal intentions.

Leak Prevention

Properly managing underground storage tank systems will reduce interruption to the intended use of the tank system and the cost of contamination cleanup.

Owners/operators of a UST system must abide by the requirements established in the Code of Federal Regulations, 40 CFR Part 280: Technical Standards and Corrective Action Requirements for Owners and Operators of Underground Storage Tanks, as well as the regulations of state and local governments. These regulations require that storage tanks be equipped with a leak detection system and spill and overfill protection as well as maintain the required corrosion protection. Most states have their own specific requirements for routine inspection and testing of USTs and release detection systems.

We recommend owner/operators initiate their own routine inspection of spill buckets, overfill alarms, fill and monitoring ports, dispenser hoses, nozzles and breakaways, dispenser and piping sumps, and spill and overfill response supplies. It is also recommended that owners/operators conduct routine inspection of tank field monitoring wells and establish standard operating procedures to prevent and detect product delivery errors.

Finally, it is strongly suggested, and in many instances required by law, that all leak detection and corrosion performance tests and any maintenance and repair activity be documented and maintained as part of the record keeping associated with the tank system.

Are you interested in finding out more about spill prevention? Do you need assistance with tank management or inspections? Do you need help with a leaking UST? Ambipar Response EMS has the experience to keep you in compliance with environmental regulations and decrease your potential liabilities.