By Chris Summers
The cost of the project was £5m
Construction firms were charged up to £90 per lorryload to dump spoil, making the project self-financing
Around 60,000 lorryloads were dumped - a total of a million tonnes
The four hills are part of a 45 acre (18.5 hectare) park
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.
At any one time there are dozens of large construction projects under way in a city the size of London.
Each one generates vast amounts of clay, topsoil and rubble which has to be dug out to enable the builders to put in the foundations of the new edifice.
So what happens to it all?
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.
Over Easter a church group erected a cross on the top of one of the hills
Mr Fink realised that a number of huge civil engineering projects were about to get under way in west London, including the redevelopment of Wembley stadium and a giant shopping centre at White City, and knew the builders would need to get rid of large amounts of what is known in the trade as spoil or "muck away".
"We offered to take all this spoil at our site, charging between £70 and £90 per lorryload, which meant the developers only had to haul it 10 miles rather than 100 miles to a landfill site," says Mr Fink. This process reduced the overall "carbon footprint" of sites such as Wembley and White City.
Around 60,000 lorryloads of spoil and concrete was dumped on the site, which generated so much money the council actually made a profit out of Northala Fields.
The spoil was used to create the four hills while the concrete was crushed and used in gabions - walls surrounded by steel cages, which provide a spiral path up the tallest hill.
The famous twin towers were demolished in 2003
It was not the first time a development had been funded by taking spoil, but the size of the project was a landmark. "It was the first time it had been done on such a massive scale," Mr Fink says.
"Initially there was a lot of mistrust locally from residents and local councillors who feared the idea of dumping and were worried about toxic spoil."
But eventually they persuaded the council and the locals that the project could be done without harming anyone's health or affecting house prices.
Northala Fields, the new park which includes the hills, has now opened to the public and has been getting a positive reaction locally.
When it is completely finished it will offer two playgrounds, a large area for walking and several ponds for fishing and the hills also have the added benefit of helping to muffle traffic noise.
As for Mr Fink's firm, Form Associates, they are hoping to recreate the success of Northala with a huge development in Manchester, Irwell City Park.
Here is a selection of your comments.
The reverse happened years ago when the 'new town' of Peterborough was developed with the aggregates extracted from the beautiful landscaped parkland known as Nene Park.
An area of scrubland that used to have some nice biodiversity now supports nothing at all. A huge step backwards for the greening of London.
Marquee Mark, Wallingford, Oxon
Isn't it still landfill, just "pretty" landfill?
Jim C, Epsom, UK
Would anyone mind using some of that rubbish to fill the great big hole left in Bayston Hill.
John, Bayston Hill
The same concept has been used to create Church Marshes Country Park on a former landfill site in Sittingbourne in Kent. Almost 500,000 cubic metres of fill have been used to create a haven for the public as well as endangered species such as the Great Crested Newt and Shrill Carder Bee, all paid for by construction firms looking to get rid of waste fill - a real win-win situation.
Chris Procter - Friends of Church Marshes Country Park, Sittingbourne, UK
North Weald Golf course in Essex is being extensively landscaped thanks to earth from the Olympic site in Stratford.
Barry, Upminster Essex
I am amazed no one thought of this before. Slag heaps from the coal industry have been dotting the northern landscape for generations. Only in the last 20 years or so have they been landscaped and made to look nice.
Perhaps the government could look at making this a viable option for a lot of developments with tax breaks for not using landfill?
Andie Riley, Leeds