A circular hole

Wow a really fasinating picture. I wonder how much gas seeped in to the soil over the years

Not much if Elf and Safety did it s job (some hope!!!) sad# sad#

The gasometer is a separate metal self compacting tank, so the bricks and ground did not come into contact with the gas, except for residual escape. I have diagrams here somewhere of the arrangement of a gas producing plant of that time.