oil leak

[what..the?]

my oil tank have leaked about £150-£200 pounds worth from a fixture, I am upset I have lost that money but I am worried what impact the oil into the ground may have. I live on a solid slate bedrock with a thin soil layer, we are having an extension build very close the the leak but not on top.

Could this cause foundation problems? to the existing house (oil tank is to the rear of the property very close) or the new extension.

Is this something that needs digging out, would the ground around and under the tank need digging out we will have lots of clean spoil we could refill with.

[The Builder]

I doubt if anything will grow around the tank for a while, but otherwise, I can't think of any foundation problem. I demolished a small garage/petrol station once, to put up a new building. I had a "ground investigation" done by a Consulting Engineer. He found nothing out of order. It was mainly to keep the NHBC happy. They worry about contaminated ground.
Be prepared for your digger driver to comment on the smell when he starts digging. He'll think he's fractured a pipe ;o)

[what..the?]

thanks for that :)