Underground Storage Tanks
It has been estimated that as many as 25% of the residential underground fuel storage tanks are currently leaking. Sometimes homeowners are alerted to a leak by what seems like excessive fuel consumption, most often the fuel oil used for heating purposes. This will only happen, of course, if the tank is badly corroded or otherwise damaged and the leak is quite significant. In most cases, however, the leak is not readily detectable in this manner. Even if the rate of leakage is relatively slight, over time, it can lead to a significant amount, creating an environmental contamination concern for both the soil and underground water. Clean-up requirements will depend on the type and degree of contamination. It should be noted that the age of a tank alone is not always a true indicator of its potential for leakage. Since the corrosion process associated with underground tank deterioration is, at least in part, due to the interaction of the metal tank with the soil, the type of soil the tank is buried in will significantly affect the rate of corrosion and ultimate life of the tank. Under extreme soil conditions, some tanks have deteriorated and leaked in as few as seven years.
When a leak is ultimately discovered and the tank is removed, significantly contaminated soil must also be removed and disposed of properly. The additional cost involving the contaminated soil can be significant. Most cases are not subject to reimbursement by any form of insurance. If the leakage has actually gotten to the point where it has affected the water table or groundwater supply, the cleanup costs can skyrocket. In such cases, usually long-term monitoring must also be done after costly corrective measures have been undertaken.
It should be noted that the age of a tank alone is not always a true indicator of its potential for leakage. Since the corrosion process associated with underground tank deterioration is, at least in part, due to the interaction of the metal tank with the soil, the type of soil the tank is buried in will significantly affect the rate of corrosion and ultimate life of the tank. Under extreme soil conditions, some tanks have deteriorated and leaked in as few as seven years.
The only way to accurately determine the condition of the tank and soil is to have them tested. There are several different types of evaluations available for underground tanks. Subject to any local restrictions or requirements, tank evaluation methods available may include profiling, hydrostatic (standpipe), petrotite (volumetric), or underfill.
There is no one method that is 100% effective in determining underground storage tank leakage, short of removing the tank from the ground and performing a physical inspection. Naturally for an initial evaluation of an underground storage tank, in most cases removal and inspection of the tank would not be a feasible approach. However, since the primary issue of underground fuel tanks is one of possible contamination, certainly soil sampling by itself or in conjunction with other testing methods is a viable option. The profiling method uses soil sampling and a measurement of the potential corrosion rate of the tank to determine the likelihood of deterioration and leakage.
Hydrostatic and volumetric testing (overfill methods) generally require adding a minimal amount of positive pressure (usually 3 to 5 psi) to a tank that is filled with product (for example, fuel oil). This is achieved by adapting an extension to the fill pipe, and filling it with product to a pre-determined height. This column of product puts a slight amount of added pressure on the tank. The column is monitored for movement. Product temperature and barometric pressure fluctuations also factor in the final assessment.
The underfill method generally requires that there be product in the tank, but unlike the volumetric and hydrostatic methods the tank doesn't have to be full. A slight negative pressure (3 to 4 psi) is applied to the tank and the tank is monitored for pressure change. Depending on the specific underfill method, a listening device may also be inserted into the tank.
One caveat with the “pressure” methods is that the fuel supply to the systems fed by the tank must be shut down during the evaluation process, which on average is a two or three hour process. Also, with the overfill methods the tank must first be filled, and additional product will be necessary to fill the column.
Even if a property is not currently using fuel from a buried tank, there may be an abandoned tank. Unconnected pipes that enter the structure below grade or pipes sticking up from the ground may be a sign of a buried tank.
If there had previously been a conversion to a different type of fuel, the owner or fuel supplier may have information on previous conditions or the status of any buried fuel tanks, if one had been present. Even if a tank has not leaked previously, some local regulations may require special abandonment procedures or even tank removal.
A home inspection does not include identifying or locating buried fuel tanks or an evaluation of their condition. For this reason, homebuyers should question the owner of any property they are considering purchasing for knowledge of tank conditions or any prior evaluations. Local authorities may also be able to provide information if tank leakage or contamination issues have been problematic in the area. If a buried storage tank is located on a property, whether active or abandoned, an evaluation of the tank is recommended to determine its condition and whether it has leaked.
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