Old flue removed and the hole left reeks of heating oil

Airship · December 12

We recently had our old furnace flue removed as part of replacing a gas gravity furnace system and ducting. The flue pipe was sheet metal with a clay liner, sitting on what appeared to be a concrete base on the garage floor.

After the abatement contractors took down the flue, it left an approximately 16" x 16" hole in the garage floor that is giving off a very strong petroleum / oil smell. The contractors said that the flue pipe had an opening in the bottom down into the hole, but it's not clear if this was by design or due to corrosion over time. They didn't know what was causing the smell.

The house is in San Francisco and was built in 1939. We thought that the gas gravity furnace was original to the house, but with this smell, we're starting to think that it may have previously had oil heating.

Other than the smell, the potentially related evidence I can see in the garage are two unexplained bolts in the floor near the flue and what looks like a cut-off pipe about seven feet away towards the front of the garage. There's no smell coming from the pipe and it appears to be filled in. There's also a potentially suspicious area in the flue hole (highlighted in yellow).

Unfortunately, the HVAC contractors were scheduled to come the next morning and they installed the new furnace over part of the hole before it was fully dealt with. They partially, but not completely, filled it in, and the smell is still present. Luckily the furnace base can be removed, but there's now not nearly as much access to dig out the hole as before.

I had a tank search company come out and they agreed that the smell was bunker oil / heating oil, but they didn't see any other direct evidence of a tank. Hopefully if it had one it was above ground and not buried under the garage. And maybe the smell is just old oil flue fumes and prior incomplete combustion byproducts that settled at the bottom.

We're trying to figure out how to best deal with the hole so that this isn't an issue going forward. My thinking is that the following needs to happen:

Dig out the hole to remove all material that was in direct contact with flue gas
Potentially apply Odorgon powder or spray
Install vapor barrier in the hole
Fill in the hole with concrete
Paint the concrete with a primer / sealer barrier paint

Has anyone come across something like this before? Are we missing anything in our plan to resolve it?

Jamie Hall · December 12

This is not good. I wouldn't be a bit surprised if there had been an oil fired unit in there at one time — otherwise you wouldn't have a fuel oil smell — at least not in San Francisco. The question is whether or not it is just residuals from the old flue — or whether you had a genuine spill, and the only way to tell is to take samples of the soil from the area and have them tested.

If you find fuel oil contamination in there you have major problems.

I don't want to know who you are. I don't want to know just exactly where you are. I never heard of this thread. Burn before reading.

Waher · December 12

a hygienist would have to look at it. Best case they direct a small amount of soil be removed to verify there wasn’t a spill. That soil would be replaced with a clay cap to absorb any remaining residual VOCs, a vapor barrier installed above to block vapor rise into the house, then new concrete with a sealed finish applied above.

Airship · December 12

Thank you both! I agree that all signs point to there being an oil furnace in the past. I don't think there's any other reason we'd be smelling oil. Whether or not there's an oil tank buried under the garage is a whole nother can of worms.

It makes sense that we'd have to do a soil test to determine exactly what we're dealing with in the hole. I'll look up some environmental testing firms and see what they say.

Old flue removed and the hole left reeks of heating oil

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