Provian Construction digs out a giant landfill cell in south London

Provian Construction is shifting 200,000m³ of soil and clay as part of a cell preparation project to make way for south London's waste. James Stagg reports.

Despite most households now collecting tins, bottles and papers for recycling, the majority of our household waste is still sent to landfill. According to government figures, in 1998 only 7% of England's waste was recycled, but this figure has now quadrupled to 27%. However, the figures vary wildly from authority to authority and some are far more advanced than others.

Some of the more forward-thinking boroughs include Kingston upon Thames, Croydon, Merton and Sutton, who have combined to develop a joint waste strategy. The south London boroughs last month awarded a £112m waste management contract to Viridor Waste Management to help boost recycling and send less waste to landfill. This agreement gives Viridor the responsibility of collecting and disposing of 450,000t of waste and recyclables a year.

One site where this waste is processed is Beddington Farmlands Recycling Centre and landfill facility near Croydon. The state-of-the-art site includes a green waste recycling facility, a mechanical/biological treatment facility and a landfill site and associated gas power plant.

Viridor acquired the site in 2004 and, while it is helping the four boroughs exceed EU targets on waste sent to landfill, a considerable amount is still buried in the ground. This means regularly creating new cells for disposal.

Landfill cell

As part of this process Provian Construction - formerly Brett Construction - is on site creating a new landfill cell. The firm's earthworks division has secured a £400,000 contract to undertake bulk earthworks on the site and install composite linear systems, protection layers and leachate drainage facilities designed to protect waterways and land from contamination.

"Before us, Cemex had been on the site extracting aggregate, but their contract came to an end and Viridor moved in to use it for landfill," explains Provian contracts manager Geoff Milburn. "We are currently removing 200,000m3 of soil, which is stockpiled for the capping of the active landfill. We're about 30% of the way through and expect to be on site for another seven weeks, weather permitting."

Some 50,000m3 of the material removed goes to stockpile, 60,000m3 is saved for engineered clay capping, 14,000m3 goes to engineered clay cell lining and the remainder goes to restoration soils on the engineered clay cap. To remove all of this, Provian is using Volvo 40t excavators, 25t dump trucks and Caterpillar D6 dozers. Sheepsfoot rollers then move in to compact the clay.

The operation sounds simple but with the wet weather the country has endured, the work hasn't been without its problems. "We've had to halt works many times purely for safety reasons," says Milburn. "The last thing we want is a 40t excavator or 25t dump truck slipping down the cell. As soon as the soil is damp we have to look at stopping work to prevent any accidents."

Limited space

Heavy plant sliding down banks of soil isn't the only issue Milburn is concerned about. With dust carts going to and from the landfill cell next door space is limited. "It's a very busy landfill site serving a large area so we've had to make sure our haul routes don't interact with Viridor and compromise the smooth working of the site. To make sure we're not in the way, we've constructed new access routes."

Once the logistical problems are overcome and earthworks complete, the cell is constructed in layers. First, the good quality clay is returned to the base in a 1m-thick layer. On top of that sits a geotextil grid, followed by bails of recycled tyres, which are specified instead of aggregate by Viridor to act as a drainage layer.

"The bails of tyres are bought by Viridor as an environmentally friendly alternative," explains Milburn. "Something has to be done with used tyres and it might as well be this. If you can find a way of completely disposing of used tyres you could make yourself a rich man."

Extraction system

Once the site is filled with waste, Provian will return to cap it with clay and restoration soils incorporating an extraction system to pipe gasses emitted from the landfill to power generation facilities. "The engineered clay capping is 1m thick and has a 300mm clay protection layer on top, followed by between 1.5m-5m of restoration soils," adds Milburn. "We also drill down gas wells that are connected to a ring main. This transports the landfill gas to a power plant on site."

The power plant generates 3MW of electricity, the majority of which feeds directly into the national grid, ensuring that even from the waste that cannot be recycled, some environmental balance is achieved.