Major construction projects produce hundreds of tons of rubble and spoil, but is there an environmentally-friendly alternative to landfill? Four hills which have sprung up on the outskirts of London provide the answer.
For years large quantities of it ended up simply being dumped in landfill sites.
But now, in a more environmentally-conscious age, imaginative solutions are being provided and one of the most innovative has taken shape beside the A40, the main road leading from London out towards Oxford and Birmingham.
Eight years ago Ealing Council wanted to redevelop a 45 acre (18.5 hectare) area of derelict parkland in Northolt, which had become an eyesore.
They recruited a firm of consultants, led by landscape architect Peter Fink, who came up with a solution which included the creation of four man-made hills on the south side of the carriageway. It would become part of a park called Northala Fields.