How clean is your valley?

Regeneration of a former steelworks site in Ebbw Vale is under way.

The Welsh valleys were synonymous with mining and manufacturing for two centuries, but their decline in terms of activity has been just as acute as their sudden transformation in the Industrial Revolution. During the past 30 years, coal mining and steel making have disappeared completely from the area, leaving high rates of unemployment and large tracts of derelict former industrial land.

The typical response to this decline has been to clean up the land as quickly as possible and build light industrial units in an attempt to generate new employment. But a different approach is being taken at Ebbw Vale, where a decision by Corus to close its steelworks in 2002 has left 81 hectares of empty land alongside the town.

“We were acutely aware that the site is actually bigger than the town, so what we do here will have a huge impact on the community," says Richard Crook, project director for the scheme to regenerate the site. "We've decided to look at it from a quality, long term perspective rather than a short term fix."

Consultant Halcrow has drawn up a masterplan that includes not just business premises and housing but also a new primary school, a learning campus for 3,500 students, a hospital and the terminus for the new Ebbw Valley rail link, as well as 28 ha of public open space. Mr Crook concedes it is likely to take at least 10 years and £350 million of private and public money to bring this masterplan to fruition. But he is determined that the result will be a fully sustainable development.

Quality and sustainability are the watchwords for the regeneration, which is being spearheaded by the local authority, Blaenau Gwent County Borough Council, and the Welsh Assembly Government. Best environmental practice is being applied to everything from the clean up operation to carbon usage in the completed buildings - starting with the most appropriate way to deal with the contaminated ground left behind by 200 years of iron and steel production.

"The initial engineering approach to reclaiming the site was going to be to import 250,000 cubic metres of fill and cover what was there," says Mr Crook. "A quick calculation shows that would require 100,000 lorry loads of material, which works out at about 2,000 lorries a week going through the town. If sustainability and quality are what we are about, then we had to do it in a sustainable way - which means dealing with the material on site," he says.

This is now the overriding philosophy for the clean up, and a source of pride for both the client and contractor, Nuttall, which has a £9.5 million contract for remediation. Viv Cole, Nuttall's project manager, estimates that only a tiny fraction of material perhaps as little as 20 cu m will have to go off site. The rest will be treated in situ using a mixture of bioremediation, soil washing, screening and crushing and reused as fill.

Corus vacated the site in 2005, having demolished most of the buildings. What was left behind was an entirely artificial environment, with the ground built up over the years from waste materials and by products, including slag. Much of the area is covered in 600 mm thick heavily reinforced concrete all that remains of the steelworks' two main structures, the hot and cold mills. Outside the footprint of these two slabs, much of the ground is known to be contaminated with hydrocarbons, while the material beneath the slabs could contain other contaminants.

Nuttall's strategy is to bioremediate all the ground that is contaminated with hydrocarbons (about 100,000 cu m), and excavate, screen, test and segregate a further 650,000 cu m, taken from below the concrete slabs and elsewhere on the site. This is unlikely to contain hydrocarbons but may contain “expansive" slag, which could affect foundations of new buildings if left in place. There is also 7,000 cu m of railway ballast from old freight lines to be taken up, cleaned and screened.

In addition, all the concrete from the two slabs will be broken out a total of 100,000 cu m tested, screened and crushed for use as drainage material, fill and capping elsewhere on the site. As part of its tender, Nuttall also vowed to reclaim 7,000 tonnes of rebar and offset the income from recycling this against its tender price.

As a result, the slab demolition is a complex activity, requiring excavators equipped with demolition equipment to break out the concrete, cut through the steel and pull it free.

Timing of this activity is also important, as Nuttall is making use of the flat concrete slabs for crushing, screening, segregating and storing the different types of material it finds. The main slab of the hot mill is being stripped out from north to south, while material in the "central valley" is being removed from south to north. This valley will eventually contain a new railway line and linear park, including a wetland park running the length of' the site.

"The real logistics come in when we start demolishing the slab," says Mr Cole. "The material under the slab is potentially contaminated, so we have to take it to the bioremediation area and then take samples for expansive slag, clean and separate it to make it ready to use as fill."

The slab of the cold mill, on the eastern side of the site, has been set aside for bioremediation. This involves using natural bacteria to break down hydrocarbons the major form of contamination on the site and will be used for about 100,000 cu m of excavated material.

Nuttall has a waste exemption certificate that allows it to use green waste (compost) as the bacterial medium for the bioremediation. Contaminated soil is mixed with this green waste in a ratio of 5:1, covered and left for about six weeks with air passing through it to encourage bacterial activity.

Temperatures soon reach 40 degrees Celsius, indicating that the bugs are doing their job. Once it has been bioremediated, this material can go back into the works as structural fill, as long as the organic content is not too high.

Nuttall is importing a total of 50,000 cu m of green waste, 20,000 cu m of which is for the bioremediation and a further 30,000 cu m for "soil forming". Two hundred years of heavy industry on the site have left it without any natural soil, so the client has taken the innovative step of asking for soil to be “grown" on site rather than imported. Halcrow's environmental experts have designed a mix that will result in a high quality growing medium for use in the wetland park and other landscaping areas. In all, 80,000 tonnes of new soil will be made from carefully mixed green waste, colliery spoil (shale), gritstone dust and dried sewage sludge.

Both the hot mill and the cold mill buildings contained extensive basement structures, the largest of which measures 100 in x 30 in x 10 in in depth. Another is a staggering 26 m deep the equivalent of a five-¬storey building. The client is keen to find uses for some of these structures, rather than just filling them in, and has engaged the local community in identifying possible future uses. Suggestions so far include a contemporary art gallery, underground parking, sunken gardens and young people's play space.

Some of the smaller basements are interconnected and will be filled with drainage material (formed from crushed concrete or rail ballast won on the site) to provide a path for any water leaching through the site. Others are being set aside for grey water storage. At the moment Nuttall is going through the process of draining all the basements, testing the water before and taking cores of the concrete to ensure no contaminants have leached into the walls or floors.

Understandably, testing forms a significant element of the project, and Nuttall has brought specialist environmental and scientific consultant ExCal on board to handle this and for advice on bioremediation and treatment.

The contractor is currently eight months into a 16 month remediation contract that will see the site fully prepared for the proposed development. Construction of the first building the hospital is set to begin next year.

Article courtesy of Construction News (26/07/07)

Further Info

For further information, contact Peter Bishop, Head of Public Relations at:
Edmund Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484
Fax:01276 66060
E-Mail: peter.bishop@edmund-nuttall.co.uk