Tarmac smell from soakaway

[thecookies]

Hi all,
We dug a soakaway out around the front of our house a couple of days ago (had been meaning to do it since we moved in - previous owners had breeched DPC by laying a driveway on top of old driveways) to free up our air bricks.
After removing top layer (brick), some rubble and hardcore, we then hit tarmac which stank to high heaven when we smashed it up. We now have a 20cm wide/10-15cm deep soakaway filled with pea shingle to help drainage.
However...the downstairs of the house is constantly filling up with the smell of tarmac/diesel and we are a bit worried and very grossed out.
Any tips?

Is the Tarmac coming from the ground you dug through?

My first thought is that although it smells like tarmac/diesel, it's actually something else. Possibly sewer gases - could you have a damaged drain? Would explain why the tarmac smelled when you were breaking it up. It could also be that the damp problem was down to a cracked clay drain as well as breach of the DPC.

There could possibly be something dead and decomposing which has been disturbed by the work you've done and is now exposed to air.

Ah, so there was a pipe (about 5cm diameter) that was completely hidden in a cement block under the central air brick, dead centre of the house. We smashed the cement to dig the soakaway but as soon as we saw the pipe we stopped. So I guess it is possible we have upset a sewer pipe. Would we call Thames water to check?

You could try them. 5cm doesn't sound very big for a drain though. Call Thames Water for advice and take it from there. You are usually responsible for pipes on your property - the water company is responsible from the boundary to the mains in the street.

Do you have accidental damage cover on your home insurance? If so, call your insurers - they will send a drains company out to investigate. If it is sewer gases, they are dangerous. If they build up inside it could be very dangerous indeed.

I was thinking that the house builders may have tried to hide some contaminated waste on site (illegal) and the OP had disturbed this, but the broken pipe is intriguing.

It's a 1900 mid terrace so I doubt there is any waste hidden waste, surely it would have been disturbed already?
The sewer gas idea is scary, but it smells like a mix of diesel and tarmac and paint thinner - I figured sewer gas would smell like sewage...

Well diesel, tarmac and sewers gases all give off sulphurous fumes to some degree.

The smell will be coming in through the airbricks you have uncovered, at least in part.