The bottom line:

Average: 10-15 Years

At 20 years – the risk of leaking increases significantly

BUT – there are many factors that can decrease the lifespan of an underground storage tank significantly.

underground oil tank

Factors that affect the lifespan of an underground oil tank:

  • Exposure of the tank fill pipe to water entry or runoff

    • Particularly if the fill pipe is installed flush with the ground rather than raised. In this situation, rainwater and snow will sit against the pipe for long periods, increasing the likelihood of corrosion and leakage.
  • Damage to the tank during installation

    • If the tank was scraped in any way during its installation, it could create a weak, thinner spot that is more prone to leaks.
  • Damage to tank & piping from surface activity

    • If the tank is buried below a driveway, near the street, or in any area that experiences traffic from vehicles and/or heavy machinery, the added pressure to the tank could cause damage and, therefore, leakage.
  • Damage to tank, piping or vents from vehicles or machinery

    • If vehicles, mowers, tractors, etc. come in contact with any of the pipes or vents near the surface, it could cause damage to the tank that might not be visible from the surface, increasing the potential for leaks.
  • Corrosive soils

    • Some soils are much harder on steel, copper lines and brass fittings than others, and can quickly cause damage to the tank and hardware, resulting in leakage at many different points.
  • Conductive soils

    • Clay soils and tightly packed, moist soils can be very conductive and carry electrical currents to the tank, increasing corrosion rates as well as the likelihood of leaks. This is especially a risk in urban areas and around electrical grounding and/or wiring faults.
  • Amount of groundwater in the soil

    • This is the primary culprit for underground oil tank leaks. The more water present in the soil, the greater the rate of corrosion to the steel tank, copper lines and brass fittings. If there is poor drainage in the area around the tank, if there is frequent rain or snow, or if the tank is near a river or body of water, there is a significant risk of leakage due to corrosion.
  • Defective tanks and/or welds

    • If the tank was manufactured with defects or if the welds were low quality, incomplete or incorrect, the likelihood of leakage is greatly increased.
  • Wrong type of tank

    • There are many cases in which the underground oil tank installers had installed tanks that were never meant to be buried. Smaller tanks, like 250g or 275g tanks, are not rated for underground installation. The steel is far too thin and weak to resist the pressure of the surrounding soil and water in the ground and will therefore leak significantly faster than others.

TIPS To minimize the risks of a leaking underground oil tank

  • Test your underground oil tank for the presence of water at least once per year.  Even if the tank is relatively new and installed properly, this is the best practice to detect a leak. If water is found in the tank, it should be pumped out immediately, as water corrodes the steel from the inside out and increases the likelihood of a leak.
  • Make sure roof spillage and surface runoff is directed away from the location of the buried oil tank.  
  • Because the back-fill around the buried oil tank will normally be less dense than surrounding soils, surface runoff or roof drainage will more readily seep into the area around the buried tank. This not only adds to the corrosion of the tank but may also increase the likelihood of water finding its way into the foundation and/or basement if the tank is close to the house.

It’s always best to have your underground oil tank removed before it gets too old or if it’s buried in corrosive soil or if it’s installed in an area that’s exposed to a lot of water.

Tank with Backhoe