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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. Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman. WHY OIL TANKS or SEPTIC TANKS FLOAT up out of the ground or up inside buildings 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. Risks of Structural or Mechanical Damage or Fuel Leak Contamination due to Floating-up Fuel Storage Tanks During Flooding At or In BuildingsOutdoors or inside as well, heating oil storage tanks that are full or nearly full are less likely to float up out of the ground or to move off of their moorings during area flooding. During installation of plastic or fiberglass storage tanks for fuel or as septic tanks, the installer can include anchors to help protect these light storage vessels from movement during flooding. But generally installers of heavier steel storage tanks omit tank anchoring systems from their installation. Outdoors buried steel oil tanks are simply placed into an excavation and connected to fuel fill, vent, and supply piping. And above-ground oil storage tanks both outdoors and indoors are typically installed relying on little more than gravity to hold the tank in place top its legs. If exposed to flood waters, and depending on the volume of oil that they contain, oil storage tanks of any material, steel, fiberglass, or plastic, may float off of their support or moorings. Even if the tank itself is not damaged, an oil spill is likely as this movement will rupture oil supply piping lines and connections. And movement can also damage the oil storage tank itself or the movement of the tank may damage other building components & mechanicals. Julie Satow reported in the New York Times (January 2013), during flooding caused by Hurricane Sandy (New York, 2012),
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