Site remediation: Filth Avenue (Special report on regeneration)

One of Europe's most contaminated sites, a 98h cokinh works near Chesterfield, is undergoing a huge clean-up. Phil Bishop meets the remediation team.

When the doors of The Avenue Coking Works near Chesterfield closed for the last time in 1992, the national coal board simply walked away. What was left behind was a legacy of industrial pollution.

The site had begun life in the 19th century as a colliery, which was later expanded to a lime and iron works. Commercial by-products of coke production included benzole, creosote and sulphuric acid. All the waste products over the years had simply been co-disposed – solids and liquids – in sludge lagoons. On closure, there were 5,000 pipe sections and 500 tanks full of unknown chemicals.

In 1999 the task of clearing this mess fell to the East Midlands Development Agency (EMDA), which had been given ownership of the site. By the second half of next year the clean-up will finally begin.

It is a massive undertaking. The site covers an area of 98ha and there is approximately 2,000m3 of slurry in the lagoons.

EMDA project director Mike Fenton explains the challenge: “When EMDA took over the site in 1999, no one knew what was there. Records were incomplete. We had to demolish the chemical works before we could get at the ground to see what was in it.”

The biggest challenge, says Fenton, is treating the slurries. Rather than ship it off to landfill and export the problem, the plan is to treat it on site and, having made the material inert, return it to various parts of the site.

EMDA is committed to employing best practice and the project has been earmarked as one of six demonstration sites under a European Union initiative to share best practice in cleaning contaminated land. As far as possible, everything will be reprocessed, recycled and re-used. Scrap metal, old tyres and plastic will be the only material actually leaving the site.

In May, the VSD Avenue joint venture was brought on board as preferred design and build contractors. This group comprises civil engineering contractor Volker Stevin, Deme Environmental Contractors (DEC) and waste management specialist Sita Remediation. VSD Avenue is also supported by environmental consultants Entec.

Fenton explains that the contractor was included early so that it could be involved with the detailed design work and agreement could be reached over the appropriate allocation of risk to ensure best value for money.

Over the past seven years there have already been extensive site investigations by EMDA and consultants Jacobs (formerly Babtie Allot & Lomax) and Turner & Townsend, as well as major demolition works.

However, further investigations are now being carried out by the contracting consortium.

“We always thought more ground investigation would be needed,” says Fenton. “We are now doing this to further identify the nature of the contaminates and its limits.”

“We are carrying out screening tests on various samples,” explains senior site agent Rob Dalton of Volker Stevin. This work includes sampling contaminated water to determine the design of water treatment works that VSD Avenue will design and build.

“There’s a fair bit of work involved in the remediation design,” he says.

Treatment technologies

A combination of treatment technologies will be used depending on the level and depth of contamination across the site. Some materials such as metals can just be screened or washed out of the soil, while other compounds need to be biologically or chemically degraded under controlled conditions. But for the highly toxic sludge a cutting-edge technique called thermal desorption will be used.

Dalton explains how it works: “The contamination gets oxidized and all the gases are treated so that the only thing coming out of the chimney is water condensation. The remainder is a clean and inert fill material.”

The thermal desorption process has already been proven by DEC, a Dutch company, in earlier trials. DEC transported material to its facility in Rotterdam. There, contaminated sediment was put through a kiln at temperatures up to 600°C to drive off contaminants such as poly-aromatic hydrocarbons (PAHs) and cyanides. The soil was then damped down to cool the material, reduce dust emissions and to create a material suitable for re-use. All of the contaminants that are driven off form a vapour, which is then passed through an afterburner. The afterburner operates at temperatures of between 850°C and 1,050°C, which breaks down the hydrocarbon vapour contaminants to form water and carbon dioxide. The resultant gases are then passed through a series of ‘scrubbers’ to remove all other contaminants before venting to the atmosphere.

Remediation works

At The Avenue, this will all be done on site. A massive thermal desorption plant the size of a football pitch is to be built and this will be the largest single element of the remediation works.

A total sum of £104.5m has been allocated for the whole project, with funding coming from government and managed by national regeneration agency English Partnerships through its National Coalfields Programme, which focuses on returning derelict colliery sites to beneficial use. There are 110 sites in the National Coalfield Programme, but Fenton says none are as heavily contaminated as The Avenue.

Of the total budget, roughly half is being spent on land remediation, with half being spent in advance on demolition, clearing the site and a vast array of site investigations and tests.

Once the design is fully worked up, a formal planning application will be submitted and work should begin by late summer. At this stage, VSD Avenue is not formally tied into the contract, but as it is preferred contractor and already on site doing the preparatory work, it is expected to stay there.

According to EMDA’s schedule, by 2011 the site will be clean and by 2012 it will be ready for development. The master plan envisages 25ha of mixed-use development and 73ha of nature reserve and parkland.

Despite its grossly contaminated nature, The Avenue is home to several rare species of flora and fauna. EMDA is working closely with the Derbyshire Wildlife Trust to develop plans to protect these species and their habitats while works are underway. Additionally, new areas of scarce wetland habitat will be created to support these species into the future.

Fenton says the opportunity is being taken to build a flood prevention reservoir as well, to protect 800 properties in Chesterfield that are prone to flooding.

The remediation strategy has been approved by the Environment Agency, which is also jointly developing the flood alleviation measures.

Paul Tullett, area manager for the Environment Agency, says: “The Avenue site has been the cause of serious pollution for years, with coal tars seeping into the River Rother. This scheme will see an end to this pollution, and leave in its place a valuable asset for local people and wildlife.”

[Contract Journal, 15 November 2006, p 34-35]