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Floating oil storage tanks & floating septic tanks: this article explains why some buried oil tanks or septic tanks float up out of the ground, what that event means to the property owner, and how to prevent oil tank or septic tank flotation.

See SEPTIC TANKS for information about septic tanks, drainfields, and onsite waste disposal systems.

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WHY OIL TANKS or SEPTIC TANKS FLOAT up out of the ground during heavy rains or flooding

The photograph at the top of this page and this close up show an old abandoned oil tank which has burst up out of its grave in a thicket along a creek in New York.

Recent rains and area flooding brought water level above the top of the ground in which this empty and buried tank had rested for decades.

As water levels rose the buoyancy of the empty tank caused it to lift right out of its burial spot where it had been hidden. A prior owner had even unscrewed the tank fill and vent valves so that there was no evidence of its presence along this creek.

Oil is lighter than water to begin with, but an oil tank or septic tank which is in use and full is unlikely to rise out of flooded ground even so. But an empty steel, plastic, or fiberglass tank used for oil storage, such as heating oil, or for a septic tank, is very buoyant. Even a modest increase in ground water can be enough to push the tank up through the ground.

When a buried oil tank or septic tank is lifted by rising water or flooding, any piping connections to the building it serves are likely to be severed, leading to an oil spill or a sewage spill.

The tank shown in these photos should not have been installed by a creek in the first place, which may explain why it was later emptied and "abandoned" in place. Had the tank been properly abandoned it would have been cut open, cleaned, and filled with clean sand.

The fill should have prevented the buried oil tank from rising to the surface despite later rising ground water or floodwaters.

A buried oil tank or a buried steel, plastic, or fiberglass septic tank can be prevented from dislocation caused by rising water or flooding if it is either kept full or is physically anchored to the site using cables or other means.

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FLOATING UP OIL STORAGE or SEPTIC TANKS

SEPTIC TANKS

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

• Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
• National Association of Oil Heat Service Managers, PO Box 380, Elmwood Park, NJ 07407
• "Homeowners Guide to Fuel Storage," Agway Energy Products, Verbank, NY, November 1990
• Web Link Exchange: Contact Us to list your website or contact information for oil tank testing, tank corrosion research, oil industry experts
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