Before natural gas became the dominant heating fuel in the Portland area, most homes were heated with oil. Oil was stored in large tanks buried in the yard or under the house. When homes converted to gas heating, many of those tanks were simply abandoned in place. The oil was left inside, or the tanks were partially filled with sand or dirt, and the conversion moved forward without addressing the tank itself.
That was decades ago. Those tanks are still there. And they are a significant liability for the homeowners who currently own those properties, and for buyers who don’t find out about them before closing.
Why Abandoned Oil Tanks Are a Problem
Steel corrodes. An underground steel tank full of heating oil, buried in Oregon’s wet soil, does not last forever. Over decades, the tank walls thin and eventually develop holes. When that happens, the residual oil in the tank leaches into the surrounding soil. Heating oil contamination in soil is regulated as a hazardous substance in Oregon and Washington. Once contamination is discovered, cleanup is required by law.
Cleanup costs are not predictable. A minor leak with limited soil contamination might cost $5,000 to $15,000 to remediate. A tank that has been leaking for years into soil with high permeability, or one that has contaminated groundwater, can cost $50,000 or more. These are not hypothetical numbers. Environmental contractors deal with exactly these situations in Portland neighborhoods regularly.
The liability follows the property. Whoever owns the home when the contamination is discovered owns the cleanup obligation, regardless of when the contamination occurred or who owned the tank when it started leaking.
Where Are These Tanks?
Abandoned oil tanks are most common in Portland homes built between the 1930s and 1960s. Neighborhoods with dense pre-war housing stock have the highest concentration. This includes large parts of Southeast Portland, Northeast Portland, Sellwood, Northwest Portland, and the older neighborhoods of Oregon City and Milwaukie.
Tanks were typically installed in the backyard, sometimes in the side yard, occasionally under the concrete floor of a garage or basement. They are usually 275 to 550 gallons in capacity. They are buried between two and five feet below the surface.
How to Find Out If a Property Has One
A standard home inspection is not designed to locate buried oil tanks. We document any visible evidence of former oil heating systems such as fill pipes, vent pipes, and abandoned oil lines, and we note when these indicators suggest a tank may be present. But locating buried tanks requires specialized equipment and a dedicated investigation.
The most common methods for finding abandoned tanks are a probing survey, which uses a steel rod pushed into the soil to locate metal objects, and a metal detector or magnetometer survey. Environmental companies in Portland offer these surveys for $200 to $400. If you are buying a home built before 1970 in one of the neighborhoods listed above, a tank sweep is worth considering.
Checking Oregon DEQ’s underground storage tank database is a free first step. Tanks that were voluntarily decommissioned and registered are in the database. However, many abandoned tanks were never registered, so an absence from the database does not guarantee there is no tank.
What Decommissioning Involves
If a tank is discovered, proper decommissioning requires hiring a licensed contractor. The process involves excavating to expose the tank, pumping out any remaining contents, cleaning the interior, taking soil samples around the tank, and either removing the tank entirely or filling it with slurry and abandoning it in place under a permit.
Decommissioning a tank with no contamination typically costs $1,500 to $3,500. If soil samples show contamination, the cost rises significantly depending on the extent and the cleanup method required.
What Buyers Should Do
If you are buying a home built before 1970 in close-in Portland, ask for the seller’s disclosure about oil heat history. Oregon’s disclosure law requires sellers to disclose known material facts about the property. If the seller knows there was an oil furnace, they should be able to tell you whether a tank was ever decommissioned.
A prior owner claiming they don’t know is not unusual. Many homeowners inherited a property that was already on gas and have no personal knowledge of what was done to the tank. In those cases, a tank sweep before closing is the responsible step.
If a tank is found and testing shows contamination, that information belongs in your negotiation. Sellers are generally not in a position to argue with an environmental contractor’s report. The cleanup cost is real and documentable.
If the tank is found with no contamination, decommissioning costs are reasonable and the property can be cleared with appropriate documentation.
Seeing Signs of Old Oil Heat?
During every inspection of a pre-1970 home, we document any indicators of former oil heat systems. If you are uncertain about a property you’re considering, call Russ at 971-202-1311 or schedule your inspection online. We will document what we see and help you understand what additional steps may be appropriate.