The truth about buried oil tanks

A good home inspector will always advise you: If you’re considering buying a home built in the 1950s or earlier, it’s a good idea to hire a certified oil tank inspector to perform an oil tank sweep of the property. An underground storage tank (UST) specialist will be able to tell you definitively whether or not there is an underground oil tank that could potentially cause you stress or financial burden down the road.

As a new homeowner, discovering that there’s an old oil tank (which could pose a serious hazard to the environment and your family’s safety) still buried underground at your new property is a stressful and unpleasant surprise. Thankfully, there are things you can do to make sure there’s not one buried underneath your home.

Many homes built in Kelowna and the surrounding area prior to 1957 were originally heated by oil furnaces. Although oil tanks have been used to heat homes for decades, they’ve become obsolete in our region as more effective heating methods were introduced. Oil tanks are large, so they were usually buried several feet below ground (in the backyard) to save space. Installing them away from the home also minimized the impact of leakage, and reduced the risk of fire. (There are, however, instances of tanks buried in the ground and subsequently covered by an addition to the home. Watch out for this)! Oil storage tanks are mainly made of metal, and their life expectancy is about 20-30 years, so depending on several factors they will inevitably have some amount of corrosion or rust on them due to the moisture in the soil—and there certainly is the possibility of a leak.

Old, abandoned copper oil supply pipes coming up through concrete slab

What does this mean?

Oil leakage from a buried tank is primarily an environmental concern. As the metal tank deteriorates, petroleum hydrocarbons and other substances can easily leak from underground storage tanks and contaminate soil and adjacent properties.

Most home inspectors communicate to their clients that they don’t inspect for buried oil tanks. They report any evidence of a tank including visible fill and vent lines outside, and copper fuel supply lines inside, although this is beyond the scope of inspection. Since removal and remediation of a buried oil tank is a substantial expense, we think it’s important to point out any evidence to our clients.

Remove abandoned underground storage tanks

In the Okanagan, homeowners converting from oil to natural gas (or another fuel) are required to remove the buried tank or have it properly abandoned, since most jurisdictions won’t allow it to be left in place. First, any remaining oil needs to be drained from the tank. Then the soil needs to be tested for contamination, and if there is any soil contamination, it needs to be decontaminated or completely disposed of at the time of tank removal. Finally, the soil needs to be re-tested and shown to be free of oil and contaminants, and the tank removal company will provide proof, in the form of a report with photos and details about the condition of the underground storage tank, where the it was taken to, and the amount of soil removed from/delivered to the property, etc.

The environmental testing and decontamination of the soil are usually the most costly parts of this process. Manual labour or excavators can be used to dig out the buried tank. In a best case scenario, the remediation process is not too complicated or expensive (a few thousand dollars), but in some cases, it can cost tens of thousands of dollars to clean up contaminated soil!

Our strategy 

First, we try to locate the oil tank inside the house. Tanks are almost always in the basement or lowest floor, near the area where the fill and vent pipes go through the house wall. If we can’t locate anything in the basement, we check any crawlspaces.

Oil tank fill and vent pipes that enter the ground outside rather than pass through the walls of the house may be connected to a buried tank. Basement or crawlspace pipes that pass through the walls of the house were likely connected to an indoor tank. We often find inside tanks out in the open, but sometimes they’re concealed, so we check closets and partitioned utility areas.

If possible, we follow the copper fuel supply line (and return pipe, if applicable) back from the burner. Fuel lines should be buried in or below concrete slab floors (sometimes you’ll notice a patched trench), or embedded in mortar that fills the joint between the foundation and floor. If the fuel line goes through the wall, there may be a buried tank.

Your strategy

Even if there is evidence of a buried oil tank, it doesn’t mean there is one. Ask the seller for the history of the property: whether there ever was a buried oil tank, and if so, details about when/how it was removed. If the tank was properly removed, the buyer will definitely have proof of this. It’s considered an important upgrade to the property and they should be proud to share it with you.

If the home was built in the 1960s or earlier and the seller can’t provide proof that there is no underground storage tank, ask them to have the grounds professionally inspected. Talk to your real estate agent. Do some research about the implications, and do your best to avoid any unwanted surprises.