How Water Contamination Gets into Buried (Underground) Oil Tanks
     

• How water leaks into or condenses inside of a buried oil tank - water in USTs
• OIL TANK WATER CONTAMINATION - separate article
• How Water Gets in Buried Oil Tanks
• How Water Gets in Above-Ground Oil Tanks - separate article
• How to Keep Water Out of Oil Tanks - separate article
• How to Measure Oil Tank Water Contamination - separate article
• OIL TANK WATER REMOVAL - separate article
• DISASTERS: BUILDING INSPECTION & REPAIR - separate article
• FLOOD DAMAGE ASSESSMENT, SAFETY & CLEANUP - separate article
• OIL TANK TESTING & OIL TANK TESTING COs - separate articles
• Questions & Answers about sources of water contamination in oil storage tanks
• References

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• Water enters a buried or above ground tank by condensation: as temperatures vary moisture-containing air may be drawn into and then out of an oil tank.
  
  Air leaves the tank as oil is consumed; air enters and leaves the oil tank through the oil tank vent. Moist air entering the tank from outside can bring water which, on entering the cooler tank interior, condenses out of vapor form into water droplets which can, over time accumulate.
  
  
• Water enters a tank filler pipe: from roof spillage onto the tank or filler top (particularly and obviously if the filler cap is left off), or from ground or surface runoff entering the oil storage tank (particularly and obviously if the filler cap is near, at, or below ground surface level).
• Leaving off an outside oil tank filler cap for a few days is not itself a likely source of a problem unless the filler was exposed to heavy rain, roof runoff spillage onto the open filler pipe, or surface runoff entering the tank (such as for a filler pipe flush with the ground).
  
• Water leaks into a buried oil tank from an actual tank perforation that admits ground water, or from a bad plumbing fitting on the tank. When oil levels in the tank is below an oil tank perforation or a leak in oil tank piping, it is possible for ground water to leak into a buried oil tank just heating oil may leak out of the oil tank when it is filled above the perforation or leak point.

• Water leaks into the buried oil tank from a faulty filler cap gasket around the oil tank filler pipe plug, especially at installations whose oil tank filler pipe is located in a box whose top is flush with the ground surface (see our photo, left).
• Water leaks into the buried oil tank from an oil tank vent pipe that is missing a cap to protect against rainwater or roof runoff spillage into the tank, especially if the vent (or filler pipe) are located under the roof's drip-line.
• Water leaks into a buried oil storage tank from leaky oil piping fittings. R.W. Beckett recommends that [Quoting]
  All pipe fittings must be tightened securely and have the threads sealed with a resilient compound that can endure the environmental variables in temperature. Any loose or poorly sealed [oil tank fuel piping, fill, or vent piping] joints can permit ground water to infiltrate the [oil] storage tank.
  
• Water is delivered to the oil tank along with the heating oil fuel: This is not common, but it is possible to get a delivery of "bad" heating oil that is water contaminated, especially if the oil truck happens to fill-up at the oil storage depot when an oil barge is unloading oil since during that operation water which is normally kept in the bottom of oil depot storage tanks may be stirred-up.
  
  Most oil companies know to avoid this problem and some also have water filters installed at their oil trucks. No oil company is going to admit that they picked up and delivered water-contaminated oil to your home so don't waste time asking them if they are guilty of this crime.
  
  R.W. Beckett referred to this [quoting] "possible but rare contributor due to storage and maintenance practices in the [heating oil] distribution system. Large bulk [oil storage] tanks must be checked for condensation accumulation and bled periodically.
  
  If this is not done conscientiously, then it is possible for water to be drawn out with the oil when the stocks are extremely low or when the bulk storage is filled and the water is forced into temporary suspension.
  
  Fortunately, [the heating oil sales and delivery] industry has implemented effective maintenance measures and this has been virtually eliminated. However, if water and sludge are found in a tank that does not have a leak, then it must be thoroughly pumped out, cleaned, and treated with a chemical additive that disperses water, sludge and neutralizes bacterial growth."

• The Home Reference Book - the Encyclopedia of Homes, Carson, Dunlop & Associates Ltd., Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop, and from the InspectAPedia bookstore. The 2010 edition of the Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.