Go Earthworms!

Throughout Britain, hundreds of sites where there were once petrol stations are now sitting empty, and seemingly clean. But in fact, the sites are unusable because of the leftover contaminants from the petrol and diesel.

Normally such contaminants would, in due course, be dealt with by micro-organisms that make their living out of cleaning up human beings’ mucky stuff. But the contaminants in this case are very small and hide away, as it were, amongst the soil particles, making their almost unreachable by the micro-organisms.
Enter the heroes: our old friends, the earthworms.
Put to work in the soil where the petrol and diesel contaminants lie, the earthworms chomp their way through it, and leave their excretions all over. The excretions include the now-revealed contaminants, and the way is cleared for the micro-organisms to do their part of the task.