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What  happens when a home inspection finds a possible underground oil tank?

A common request our office receives regarding a tank sweeps.

"Hello, I'm selling my home and we suspect that the buyer did a tank sweep with a metal detector vs GPR. They supposedly think they found a tank on the property. We do not see any evidence of a tank, nor was one disclosed by the previous owner (who bought the home in the 70s, house is 80 years old). Is it possible that this 'tank' is just a gutter drain pipe, part of our sprinkler system and/or rubble backfill such as a chunk of concrete sidewalk with rebar or metal containing soil? If so, would a GPR scan be conclusive? Thanks."

This is a common situation we get from property owners who are told they have a buried oil tank.   The owner has the question regarding if the meta detector is reliable.    Here are some common talking points...

1. The property owner is unclear how the suspect tank was found.  Was it found with a Metal detector, or  Ground Penetrating Radar or both? (both GPR and a metal detector would be best) The solution would be having the owner receive a copy of the Tank Sweep Report so they would have a baseline regarding what they found and where. Yes, every professional service should come with a report, no report, then question how professional the service was.
2. The property is over 70 years old, so while the owner has no knowledge that there was an oil tank, they also have no documentation that there was not an oil tank. A 70 year old property most likely had oil heat at one point in time as oil was very popular in the past and other fuel sources such as natural gas was not commonly available or financially appealing until the 1970's.
3. The tank scan found a buried object, presumably metal. If only a metal detector was utilized, you can't say 100% if the metal found is a tank as metal detectors detect metal and properties have all sort of buried metal. Metal can be in the soil naturally, you could have buried debris, buried metal pipes or surface metal (like a fence) that distracted the metal detector and have a false buried metallic signature reading. Happens all the time. A metal detector on a sandy beach is great it will find buried metal, likely a bottle cap, but people hope for coins or expensive jewelry. People paying a couple hundred dollars for someone to use an $800 metal detector to find a tank are also helpful.

The photo below was where a metal detector thought there was a tank.  There was no tank, just soils with a metallic signature.

The guy in shorts, is using a $900.00 metal detector and found a suspect tank in the front yard.

When you scan for a tank, the more expensive the equipment the better.   GPR (Ground Penetrating Radar) costs tens of thousands of dollars because it has the technology to do the job.

 Effective Oil Tank Scan or Oil Tank Sweeps like on commercial sites would use GPR as it will                            provide a signal (image) of buried objects.

The signal above shows the underground oil tank. 

Purchasers of commercial properties are more aware of the liability associated with leaking USTs (Hundreds of thousands of dollars) compared to a residential home buyers (Homeowners think a few thousand dollars is a lot.) So on the commercial side of real estate tank sweeps are completed with GPR, not metal detectors. Most environmental consultants that perform tanks weeps will use GPR and discount the cost for residential sites. Nobody wants to see someone buy a house and find a $50,0000 cleanup is required.

What if a buyer finds a suspect tank?

This is a really hard question because it relies so much on the quality of the tank sweep.    If they used GPR, if the property is likely to have had an oil tank (older the home, the more likely) and if the buried anomaly has the signature of a tank.  Well then you have to excavate and confirm that object is an oil tank.

Who pays for the oil tank removal?

Owner will pay 98% of the time as finding a hidden oil tank is a defect that needs to be addressed.

Do they have buried oil tanks at the beach (shore)?

If the home wanted heat, then yes homes along the coast and on islands had buried oil tanks.  Oil was king up until the late 1970's in New Jersey.  The photo below is of a home we scanned on a barrier island.  Many older beach houses eventually converted to natural gas, as gas could also  fuel the stove, dryer,  hot water heater etc.   After conversion to gas, it was not uncommon that the tank was just left in the ground.  So short answer beach houses had oil tanks.

What if a suspect tank is found and we don't believe its a tank?

Short answer prove your opinion right and dig it up and verify its not a tank.

What is the best tank sweep?

Using Ground Penetrating Radar is the best technology for finding buried tanks at properties, period.  Can you use a metal detector to verify a GPR signal that identified a tank?  Sure, always verify the object is metal.  GPR can't penetrate metal so when a GPR sweep pings a tank, it means the radar can't penetrate the object (likely a metal tank) but there are buried concrete tanks.  Metal detectors can verify an object is metal, but a metal detector  should not be used to be your sole technology

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.

 

 

 

 

Utilizing foam to fill an Underground Storage Tank (UST) can be a cost effective approach to closing a UST.   Injecting foam into a tank can save the cost of excavating the entire tank.  Larger tanks and tanks that have access issues & hard surface coverings such as asphalt, building, paving or structures tend to be the ideal sites for foam filling.

 

Is foam filling appropriate and cost effective for every tank?

Short answer is it’s not cost effective in every situation.  People think you can just stick a hose into the tank and pump foam, but that's not the case. The tank must be exposed, entered and cleaned of all oil before foam can be injected. Also, residual oil in the tank breaks down the foam, so the tank must be thorough cleaned of oil or else you will have an issue making proper foam.  In short, you have to enter and clean the tank and for small tanks, it might take that much more effort to remove the tank, since you already excavated part of the tank to enter and clean it.

 

No matter if you foam fill a tank, fill a tank in with sand/slurry or remove the tank there are still a set of tasks and associated costs that will be incurred, no matter the approach.

First, permits are required so the work can be inspected by the local municipality.

Second, the tank has to be excavated to some extent so the tank can be opened, entered and cleaned. You see, you have to clean the tank of all liquid prior to filling it or removing it. Cleaning entails going inside the tank. Now depending on the size of the tank, the physical act of exposing the top of the tank may actually entail exposing 60% to 80% of the tank, which at this point, it may just be another 10 to 15 minutes to uncover the rest of the tank, making removal not that much effort.

Third, once the tank is cleaned you need to test the soil, which entails cutting holes in the bottom of the tank. This actually takes longer than someone would expect as the person who cleaned the tank, has to leave the tank, change work clothing to cut these holes. Where as in the situation when you remove the tank it is much easier to sample the excavation as the soil is exposed.

Finally, you have the task of backing the area. If you remove the tank, backfilling is fairly straight forward as you have an open area to fill in.

If you are leaving the tank in place, you are tasked with placing material in the access hole you cut in the tank and pushing it to the far end of the tank. Remember the tank is a cylinder and you need to fill the cylinder completely, and sand is not self-leveling.

Utilizing foam is convenient as it is self-leveling, but you also have to make the foam on site.

 

The prep for making foam can be 1.5 to 2 hours. It’s kind of like baking you need the ingredients, proper mixture and temperature). You also have about 2 hours to clean the foam trailer post filling, as the equipment and lines have to be devoid of the foam ingredients or else they will harden and clog hoses, fitting valves, etc. so you are cleaning the kitchen so to speak. Foam filling hits a sweet spot when you have hard issues for accessing the tank with other material such as sand or concrete. Also, larger tanks (tanks greater than 2000 gallons) are more cost effective to foam fill, as you realize the advantages of the foam cost structure verse the labor of using sand or slurry.

Propane tanks are uniquely suited for foam filling as they are pressure vessels and longer than the same size oil tank.  Longer tanks disturb a larger footprint to remove, so foam filling is an ideal solution for propane tanks.