Your browser is no longer supported

For the best possible experience using our website we recommend you upgrade to a newer version or another browser.

Your browser appears to have cookies disabled. For the best experience of this website, please enable cookies in your browser

We'll assume we have your consent to use cookies, for example so you won't need to log in each time you visit our site.
Learn more

One creature's meat. . .

A heavily contaminated brownfield site can also be a home for rare wildlife. Damon Schunmann reports on one rehabilitation project with two kinds of problem.

Described as one of the most polluted in western Europe, the 99ha Avenue site just south of Chesterfield is the former home of a coking works, a coal gas plant, and a massive sulphuric acid production line.

More recently it has been a licensed landfill site. The ground is soaked with a daunting list of nasties: benzopyrene, 'blue billy' (a mixture of ferric and ferro cyanides, sulphur and sulphates), naphthalene, phenols, thiocyanate and benzene among them.

The National Coalfields Programme has committed £104.5M to rehabilitating the site, which is now owned by the East Midlands Development Agency (EMDA). Most of it will become public open space; some will be earmarked for housing and offices. But before major works can begin, consideration must be given to the wildlife that has found safe haven among the settlement lagoons and along the River Rother which bounds the site.

Water voles appear to flourish in the polluted waters, kingfishers fly above them, barn owls nest in the abandoned plants and little ringed plovers find nesting sites on the ground. Eventually Cheetham Hill Construction will build a £750,000 'giant water vole holiday resort' once the main remediation is complete.

The main task, however, is to deal with more than 650,000m 3 of contaminated soil, and to encourage an innovative approach to this challenge EMDA has gone for early contractor involvement, as pioneered by the Highways Agency.

'We want innovation to come from the contractor, ' says consultant Jacobs Babtie divisional director Jon Smithson.

'It would have been nonsense for us to specify one method.

'What we are asking the tenderers to do is indicate the combination of processes they would use, and the volumes that will go through each process.' The worst contamination is concentrated at the northern end of the site. Here run-off from a solid waste tip has caused further pollution to a complex of old unlined lagoons, which are only a few metres from the river.

Work has already been carried out to stabilise the overstressed embankment that separates the Rother from the main lagoon, but this has not stopped the pollution seeping through.

Worse still, the original construction method used for the 3ha lagoon positively encouraged the pollutants to migrate into the alluvial beds. Clay was excavated to form the lagoon and used to construct the berms that doubled the effective depth.

Unfortunately the permeable sands beneath the clay were exposed during construction.

Recent boreholes 800m from the eastern edge of the site discovered contamination 100m down in the underlying coal measures. And the silt in the lagoons has a high carbon content, three times higher than is acceptable for landfill, so sending it off site is not an option.

So, says Smithson, the only realistic alternative is to treat material on site. Up to 300,000m 3 of grossly contaminated soil will probably undergo low temperature thermal desorption, a technique which uses heat to vaporise hydrocarbons in the soil and then destroys the vapours in an 'afterburner'.

Options for treating the less badly contaminated soils include bioremediation, cement stabilisation and soil washing.

There may be others, and EMDA stresses it is open to more innovative solutions that potential contractors may put forward.

Whatever the techniques eventually adopted, cleaning up the Avenue will take a long time.

Have your say

You must sign in to make a comment

Please remember that the submission of any material is governed by our Terms and Conditions and by submitting material you confirm your agreement to these Terms and Conditions. Please note comments made online may also be published in the print edition of New Civil Engineer. Links may be included in your comments but HTML is not permitted.