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Government environmental agencies consider removing a storage tank as remediation, because storage tanks are known to rust and leak petroleum, which can contaminate soil and groundwater.    Know that the government views storage tanks as an environmental liability.  In real estate transactions, attorneys, buyers, mortgage companies, and insurance companies also view tanks as a liability and want them removed.   Many tanks can be readily removed and tested, but some tanks require an excessive amount of effort to remove, which can exponentially increase the cost.  In these situations, tanks can be closed in place, with testing, as testing will confirm whether the tank did or did not leak.  Now we deal with parties that have their own opinion regarding what is or is not possible.  Curren is licensed in three states for tank work and has completed tens of thousands of tank closures. We are experienced in what is feasible and budget-friendly for clients.

Take this crawlspace tank.  It looks like an AST, but the federal definition says it's a UST as more than 10% of the tank volume is buried below the ground.   The client said it could not be removed, Curren said it was cheaper to remove than filling the tank in place.

Filling the tank in place would have taken more labor which would have cost more.  You can see how the area looks after removal, the concave area of the tank grave.

Cutting the tank into manageable pieces allowed the tank to be removed from the space.

This project is in contrast to the next property, where a tank had a sunroom built on top of the tank.  I am sure that when this was done, the owners never thought the buried tank would be an issue.

• The subject 1000 gallon tank is right through the sliding glass doors. 
• The tank is 1000 gallons and is about 11' long. 
•  The top of the tank is 3' deep.   
• You would have to support the sunroom to remove the tank, which does not make financial sense.

The fill pipe is pretty far from the door to the room, further complicating matters.

84" inches deep

48" diameter tank

84 - 48 = 36"   or 3' deep.

For this tank, removal could be done with some engineering, but it would cost significantly more than simple cleaning, testing, and filling the tank in place.  Of course, you could also demolish the sunroom and remove the tank, but that would also cost more, and you would lose a sunroom.

In this circumstance, you cut an area of the floor out, hand dig to the tank top, 3' deep, enter and clean the tank, cut coupons, holes in the bottom of the tank, and acquire soil samples for laboratory analysis, backfill, and restore the floor.  Everything is documented in a report.

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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?

The 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 thoroughly 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 with sand/slurry, or remove the tank, there is 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 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 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. Whereas 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 straightforward, 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, 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, a proper mixture, and a 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 accessing the tank with other materials, 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 versus 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.