Abandonment of an Underground Storage Tank

Now that in most cases the removal of a leaking underground oil tank and associated contaminated soils is not required, in-place abandonment by filling the underground storage tank with an inert solid is the most common method for taking a buried heating oil tank out of service. It is essential that the proper method of tank abandonment is used, and that the abandonment procedure is properly documented.

Also, please note that even when not required by State regulations, buyers, lenders, and other stakeholders may require the abandonment of the tank prior to the sale of the property, whether or not it has leaked.

Do I need to abandon my underground oil tank?

If the tank has not leaked then you do not have to do anything concerning the tank. However, many underground oil tanks still contain oil which can cause environmental problems in the future, even if they have not yet leaked. Surface oil leak from underground oil tankCedar Rock recommends the proper abandonment of the tank in these cases to prevent future problems arising, such as the surface overflow leak shown in the photo to the right.

Even if the tank has leaked, in most cases the NCDEQ will not require the tank to be abandoned or removed, nor will any environmental cleanup or assessment be required.

What MUST be done?

A leaking oil tank must be reported to the State, and before the property can be conveyed it is also necessary to file a Notice of Residual Petroleum for the property. This will also lead to obtaining a “No Further Action” (NFA) letter from the State. Generally, a NFA letter is required to satisfy buyers and lenders requirements regarding the leaking tank.

Proper tank abandonment removes the possibility of the tank causing an environmental or structural issue in the future, or of it worsening an existing condition. If you are preparing a property for sale, it is a prudent step to have the property checked for leaking tanks, and to have any underground tanks abandoned. This will prevent any delay in the subsequent sale of the property.

Can a tank always be abandoned?

Tank abandonment may not satisfy NCDEQ requirements in certain situations. One common situation is the presence of water supply wells within 150 feet of the release area. These wells do not necessarily have to be in use. In these cases, some environmental assessment may be required, such as sampling the wells, before tank abandonment can proceed. Sometimes the State may require removal of the tank and the associated contaminated soils and the wells may have to be abandoned. Cedar Rock will advise property owners of the proper course of action if any of these situations apply to their property.

What to do First?

Soil samples from the native (undisturbed) soils beneath the underground storage tank should be obtained by a North Carolina Licensed Geologist or Engineer to determine whether or not the tank has leaked. A Cedar Rock site inspection usually confirms the presence or absence of soil contamination immediately. In some cases, it may be necessary to submit soil sample(s) for laboratory to confirm whether or not a tank has leaked. If the tank has leaked the release must be reported to the State. The tank should then be properly abandoned in-place unless site conditions require other work to be performed.

Proper procedure for in-place abandonment of an underground storage tank

Filling tank with flowable fill. Click to play.

Video of tank being filled with cement slurry
It is extremely important that the tank be thoroughly cleaned and an excavatable, flowable-fill cement slurry be used to fill it. This prevents the buried tank from causing new, or worsening existing, soil contamination, and prevents subsidence resulting from tank collapse. Cedar Rock's tank abandonment method ensures that the tank is clean and can cause no future problems.

The slide-show on this page and the video show the stages of a Cedar Rock tank abandonment.

Cedar Rock Tank Abandonment Procedure

  1. A hole is cut at one end of the tank, to allow access to the interior for cleaning and filling activities. Any water, sludge or oil are pumped out of the tank prior to pressure washing the interior.
  2. Flowable fill, a sandy cement slurry that will completely fill the tank without leaving air pockets, is poured into the tank. (As explained below, Cedar Rock strongly recommends that sand or foam not be used.)
  3. The metal flap is folded down and the landscape restored. As the before and after photos show, no one would suspect that a tank had been taken out of service.
  4. A report with color photographs is produced to document the abandonment activities.

Proper Documentation is Essential!

A report, including photographic documentation, should be generated as proof that the abandonment was fuly cleaned of its contents and then properly abandoned. Cedar Rock produces a report, signed by a NC Licensed Geologist, for every tank abandonment, which details each step of the procedure and documents the work with photos taken at different points throughout the abandonment of the tank.

Photographic Documentation

Photographic documentation demonstrates conclusively that the tank has been cleaned of its water and/or oil, and oily sludge contents. This documentation can be used to show potential buyers and other relevant stakeholders that the tank has indeed been properly cleaned and abandoned, and that there is no risk of the tank causing further problems due to leakage. Below are examples of the photos routinely included in a Cedar Rock abandonment report.

Tank site prior to work UST fluid contents prior to pumping out

UST after fluids pumped out and tank cleaned UST being filled with cement slurry

UST filled with cement slurry Tank site restored after completion of abandonment

The importance of adequate documentation is highlighted by this example of “tank abandonment”. Cedar Rock's reporting ensures that nothing like this will happen to you!

Why an underground storage tank should NOT be filled with foam, sand or water

The following photos illustrate some reasons why the correct method of tank abandonment should be used.

The left photo shows a 1,000-gallon oil tank (approximately 10 feet long) that had been filled with foam. The tank subsequently filled with fluids (1,000 gallons) which were pumped out by Cedar Rock. You can see that the foam had been in contact with the upper part of the tank but that in the course of time it has shrunk to a greatly reduced volume. When the metal rusts away the ground will eventually subside.

UST filled with foam showing shrinkage UST filled with sand slurry showing voids from incomplete filling

The photo to the right shows a UST filled with a sand slurry. Clearly, the contractor believed that the tank had been filled but as a sand slurry does not flow sufficiently a void nearly always remains within the tank.

A tank abandoned using these methods is typically filled through a small opening (usually the fill pipe). The same small opening is used to pump out the remaining fluids in the tank prior to its filling (if the fluids are removed). Oil tanks typically contain water, oil, and oily sludge which adheres to the walls of the tank. It is not possible to remove all of this sludge from a five to eight foot long oil tank through such a small opening, nor is it possible to wash down the tank thoroughly. Cedar Rock’s method of tank abandonment ensures that all fluids are removed from the tank and that the oily sludge that typically remains in the tank is also removed. This removes any possibility of petroleum leakage from the tank in the future. In many cases, improperly abandoned tanks still contain oil and/or sludge and can still cause leakage!

The left photo, below, shows the softness of the foam that is sometimes used to fill a tank. The hand auger was simply pushed through to the bottom of the tank. In this case, Cedar Rock was asked to confirm that a previous abandonment had been performed adequately. This is a risk with a poorly performed and documented tank abandonment. A buyer may still require the tank to be checked and if there is still contamination the owner may be up for further expense.

UST filled with foam UST filled with foam not cleaned of oil

The right photo shows another tank filled with foam. The fact that the tank was not properly cleaned of its contents is obvious by the discoloration of the foam and the presence of free oil in the tank.

It is essential that tank abandonment be performed correctly to avoid further problems and expense in the future.