Coins, bottles, and other interesting objects have often been unearthed by homeowners who dig around the property of older residences. However, these homes can also be more likely to have an undesirable buried item: a subterranean oil tank.

These tanks are associated with a home's heating system, or were in the past. Ryan Smith, writing for the real estate site Redfin, says many homes have abandoned heating oil systems in favor of natural gas heat. The Environmental Protection Agency says underground storage tanks were constructed of bare steel until the mid-1980s, making them more susceptible to corrosion and leaking over time.

While this issue led to federal regulations on underground storage tanks, the rules typically don't apply to individual residential systems. The Connecticut Department of Energy and Environmental Protection says it does not regulate these tanks unless they serve five or more residential units.

However, the tanks can present health risks and other hazards if they start to leak into the surrounding soil. This problem can also lead to an expensive cleanup effort or liability issues for the homeowner. If you have a buried oil tank, it's helpful to have it inspected to ensure that it won't cause any problems.

Do you have a tank?

Even if your heating system isn't actively served by an underground tank, one may be present at your home. You can check with your local fire marshal to see if there is a record of a tank removal at your property. Homeowners who have decommissioned a tank may provide a record of this process to the next person who buys the property. DEEP will also have a record on file if an oil leak was reported at your address.

Certain telltale signs can also tell you if a hazardous underground oil tank is present at your home. Smith says the fill valve and gas meter are usually left behind if a tank was abandoned instead of properly decommissioned. The furnace may also have copper tubes that have been disconnected from the tank and pinched off.

If you suspect that a buried oil tank is on your property, you can get an inspection to confirm it and see if it is leaking. Nick Gromicko, writing for the International Association of Certified Home Inspectors, says ultrasound and ground-penetrating radar can locate a tank as well as identify any leaks.

Other tests will pressurize the tank and monitor it to see if leaks are occurring, or test to see if water intrusion points to possible openings in the tank. An inspector may also test the soil around the tank to see if it has been contaminated by leaking oil.

The age of the tank can also help you determine its risk. The New York Department of Environmental Conservation says tanks are unlikely to leak if they are less than 15 years old, but the risk of corrosion increases after this point.

Hazards

Leaks from underground oil tanks can cause a variety of serious hazards. The EPA says fumes and vapors released from the tank can accumulate in basements and other areas of a structure, increasing the risk of a fire or explosion.

Fuel can also pollute the surrounding area, including groundwater sources. Gromicko says water contaminated by benzene and other harmful compounds found in petroleum can increase the chances of cancer or other health problems if ingested or used for bathing.

The homeowner might be liable for any issues related to a leaking tank if the problem is not treated. Smith says a neighbor may file a lawsuit against you if the leak affects their property.

The cleanup process associated with a leak can also be very expensive for the homeowner, often costing several thousand dollars. The New York Department of Environmental Conservation says homeowners insurance policies may include an exclusion cause for this type of problem, leaving the homeowner to foot the entire bill.

Leak response

If you detect a leak from an underground oil tank on your property, take steps to address it as quickly as possible. Leaks can often occur gradually over a long time, but stopping them early can help minimize the remediation costs.

A leak may become apparent through an inspection or leak detection monitoring equipment, or it may be detected through other means. The EPA says you may notice a fuel odor in your home, an oily sheen on nearby water, or water that smells or tastes like petroleum.

In Connecticut, the DEEP says leaking tanks should be promptly reported to the department's Emergency Response and Spill Division. You can also contact your heating oil supplier, who might be able to help you quickly find a contractor to clean up the spill.

Take steps to shut down the system, remove fuel from the tank, or otherwise prevent more oil from leaking. The EPA says you should also remove any potential fire hazards, and that your local fire department can advise you on this process.

Treatment

Homeowners can be proactive by upgrading their underground storage tank or, if it is no longer used, decommissioning it. The New York Department of Environmental Conservation says you can consider replacing an older tank with a modern double-walled one or installing an aboveground tank.

The old tank can be excavated and removed, which will prevent the possibility that the tank will degrade over time and cause a sinkhole to form. DEEP recommends that homeowners hire a registered contractor for this process, collect soil samples to ensure that soil contamination has not occurred, and ask the contractor to provide a brief report on the removal. This document can assure buyers that the tank was safely removed when you sell your home.

Tanks can also be abandoned in place if they are in a place that is difficult to access or if the removal could damage the home's foundation. However, you should also check to see if there are any local ordinances on abandoning an oil tank.

If the tank is left in the ground, it should be emptied and cleaned. It can then be filled with an inert material such as sand or concrete. Smith says a polyurethane foam can also be used for this process.