The value of second-hand plastic has risen so rapidly that mining operations to dig it out of rubbish dumps are forecast to begin within the decade.

Waste suitable for recycling is already being dug out of landfill sites in the United States and it is thought that commodity prices are on the verge of making it a profitable option in Britain.

Rubbish dumps are regarded by the recycling industry as an untapped source of riches, with an estimated 200 million tonnes of plastic buried as landfill since the late 1980s. At today's prices of £200 a tonne the discarded plastic has a value of about £40 billion. Alongside it are smaller, but still sigificant, quantities of valuable metals, including copper and aluminium.

Peter Mills, of New Earth Solutions, a specialist in waste treatment and recovery technology, said that small-scale operations to retrieve discarded plastic from landfill were already being considered in Britain.

He said: “In the States they have gone back in and have been mining for plastic and metal. Within the UK we have an eye on it. Within the next decade, landfill mining in a controlled or limited basis is going to be viable. It reflects the commodities market and the way prices are going.”

Operations are likely to start as pilot schemes during remedial work on landfill sites, which are designed with linings to prevent waste leaking into the wider environment. So high have the price of commodities risen in the past two years, especially oil, that recycled materials are increasingly sought after. Plastics can be turned back into sheeting and packaging more cheaply than by using virgin materials and with fewer carbon emissions. They also have a high calorific value, so can be an attractive source of fuel.

Mr Mills suggested that the value of plastic would soon rise high enough that entrepeneurs would find it worthwhile to scoop out the estimated three million tonnes that was swirling around the Pacific Ocean.

A further benefit of landfill mining is that once material has been removed from the ground there will then be room to bury more waste. Local authorities face a growing shortage of landfill space.

Peter Jones, an independent waste consultant, said: “If we dig up all the landfill sites in the UK since the late Eighties we could lay our hands on around 200 million tonnes of plastics. If we were going to do landfill mining we would do it for the plastics.”

He said that most of the 1,500 landfill sites used in the past three decades had to be left for 20 to 30 years once they were closed to give time for organic material to decompose and gases to escape. Up to 70 per cent of methane emissions are syphoned off and used to provide renewable energy. Because of this, he was convinced that most, if not all, landfill mining in Britain would be delayed until after 2020.

Richard Woosnam, of Orchid Environmental, a waste consultancy, will join Mr Jones this year in London at Britain's first landfill mining conference, where they will outline its potential. “It has potential for the future,” Mr Woosnam said. “Plastics are a rich source of energy and in the right type of system they can be ... a valuable fuel.”

Landfill sites from the 1980s onwards would be the first to be considered for mining because there are good records of what is in them, including the location of hazardous materials such as asbestos, and because before then plastic was discarded in much lower quantities.

The forecast comes after The Times reported yesterday that the prices of recycled materials, including plastic, paper and metal cans, had increased greatly over the past six years. What was once considered to be mere rubbish is now providing recycling companies with a valuable source of income, but many local authorities have missed out on the green bonanza because they are locked into disposal contracts that run for between 20 and 30 years.

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