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It is not unheard of that buildings are built on top of oil tanks.  Definitely not a good idea, but the structure was typically built either before environmental regulations or without regard for the regulations, or the oil tank. 

Every oil tank that is underground and even under a building has the possibility of leaking.  When a tank leaks you may have to clean up the leak, which requires removing soils (soil remediation).  How do you do soil remediation when you have a structure over the tank?    The photo below is a garage, where the walls were supported and the floor and contaminated soil was removed.  

If you want to buy a house with a tank under the house or think of selling a house with a tank in this situation, think again.  The concern with oil tanks is they leak and if they leak you may have to clean them up and that can cost money.  I know a number of properties that owners tried to sell, but having a tank buried under the sunroom was a sticking point and prevented a sale.  The only way these houses went to the settlement table was by having the owner cut open and clean the tank and take samples to show the tank did not leak.  Yes, a project like this can cost thousands of dollars but these are costs that are the responsibility of the property owner even if they never used the tank and bought the house knowing a tank was under a structure. 

In practice, many tanks that are under a garage, house or porch we find are not leaking. Why?  Well because you have an umbrella over the tank being the structure.  The house keeps the tank dry which in turn inhibits rust.  Don't get me wrong some do leak, but the drier any metal is the more corrosion resistance will occur.

When decommissioning the tank a confirmation that the tank did not leak can be acquired by soil sampling.  This entails entering and cleaning the tank of all residual petroleum compounds (liquid and sludge).  The empty cleaned tank can then be removed and soil samples acquired from the tank excavation.    But in the case of a tank under a building where removal is not practical, you can cut holes through the shell of the cleaned tank and obtain soil samples.    

So you see there is no reason you can't take soil samples from tanks that have been filled in place.  People who own tanks do not want to take soil samples because they may get bad results.  The saying goes if you do not test you have a 100% chance of finding nothing.

The photo series below is of a tank under the crawl space floor that was cleaned and tested.  The rub was that the tank leaked and remediation was necessary.  So contaminated soil had to be removed.

The tank was removed, and the soil contamination removed.  A picture is worth a thousand words.

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Protecting your interest when you buy a property is called Due Diligence and one of the most important due diligence steps you can take is performing a tank sweep with GPR. 

Why perform a tank sweep?

Most homes built before 1980 likely had oil heat at one time, so 90% of single-family homes likely had oil heat in the past, possible several owners before.  Oil tank are made of metal, they rust, they leak and it can cost thousands if not tens of thousands of dollars to cleanup.  You don't want to buy a home that has an oil tank liability.

The home in this photo series is  circa 1920's, so oil usage was 100%. 

Buyers were told the basement had two ASTs (Aboveground Storage Tanks), that were removed. This photo shows where the ASTs were located in the basement.

But just because a property had an AST doesn't mean the site didn't have a UST (underground storage tank). 

So why bother to do a tank sweep for a property where there is documentation of former Aboveground Storage Tanks?  Simple nothing lasts forever and the older the property, the more likely that a tank may have had to be replaced.

Can you see evidence of a UST in this photo?   

It's obvious to the trained eye.

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All photos on this page are from the same property.     The buyers were told the home had oil heat, the oil tank was an Aboveground Tank in the basement, which was true but seller's failed to mention that the AST replaced an Underground Storage Tank (UST).  Or the owners didn't know that there was a UST since they didn't do a tank sweep when they bought the house.   Although the sellers had their own consultant use a metal detector to scan the site, which couldn't locate a UST.

Simple is not always best.  No doubt your current smart phone (phone, camera, computer, GPS, etc.) in your pocket is a vast improving from your phone of 10 years ago.  Most likely more expensive but it does so much more.

Having the best available technology also translate to an effective tank sweep.   A $225.00 tank sweep with an $800 metal detector, it not an effective tool for locating tanks, as the cost of the equipment can attest.

The sellers metal detector results?

The metal detector produced some deflection around the plant bed indicating a possible metal tank.    Curren scanned the area with GPR and fund the metal signature were the oil tank lines from the house to the tank. 

The metal detector then went over the adjacent driveway.  The findings?

The metal detector indicated a slight, faint response at a location about mid-way beneath the driveway directly in line with the remote fill. Due to the faint nature of the signal, possibly caused by wire or rebar in the concrete driveway pad, the location could not be defined.

When you need work performed you want to hire a professional with years of experience and the best possible tools for the job.  Curren was hired by the buyers to perform a GPR tank sweep.

Within the first 10 minutes of the Curren technician being on site, we were able to locate the remote oil tank fill which had been covered over with soil.   See photo below, the red tile probe is pointing to a round cap in the landscaping which is the tank fill.

If you were buying a commercial property, you would perform a tank sweep with GPR as that is the standard and most effective approach.  But if you are buying a commercial property, you are more experienced than the run of the mill buyer.

Curren scanned the driveway with GPR and located the tank, which the metal detector could not pin point.   Yes the owners recently redid the driveway and will have to dig up part of the new driveway to remove the tank.  Did the owners know the tank was present?

The tank is outlined in yellow lines in the photo below.  The tank was under reinforced (steel) concrete making the metal detector useless, but allowing the Ground Penetrating Radar to locate the tank.

The best service directly correlates to most experienced and using the best equipment.  Hiring chuck in a truck with an $800 metal detector, who also works out of their house, may offer an attractive price, but are you getting the best service?  Is the metal detector really the best device?

To be fair performing a Geophysical evaluation which is what a tank sweep is, can involve using multiple technologies.   When we find a buried anomaly (tank) we typically also verify the anomaly as metallic using two different metal detectors.  Trust me when you find a tank that a seller didn't know exists, they want to know it's a tank, confirming a metallic signature helps the medicine go down, it is just a metal detector should not be your only technology you rely upon.

The best tanks sweeps are performed by companies that also remove tanks.   There was no rhyme or reason as to where oil tanks were buried.  Removing tanks give you experience in how tanks are situated on a site.  Curren Environmental has been removing tanks for over 30 years and is licensed to remove tanks in 3 states.    We also have removed tens of thousands of tanks, so we know what we are looking for.