How is that stuff cleaned up? Washed away with water - or like alot of foam based fluids does it slowly just disintegrate?
Depends if that foam has fluorinated surfactants in it. If it has then it will need to be scooped up and incinerated, the burnt residue is tiny. If it hasn't got fluorine or other nasties in it then the slow discharge into the public sewerage system may be allowed, but it needs to be done to prevent polluting open waterways and closed courses. There will be a well managed drill for this at Heathrow I'm sure, due to the use of foam in training exercises.