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.