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Package deal

Remediation of a former explosives facility in Essex has adopted innovative technical and contractual approaches to reduce costs and environmental damage.

Cleaning up the historic Royal Ordnance explosives factory at Waltham Abbey in Essex is nearly complete. Soon, new owner Twigden Homes, part of the Kier Group, will take possession of the 97ha site, along with another 44ha, and start construction of the Waltham Park residential and business development as well as newly established parkland and highways.

In an innovative approach to the transfer of brownfield land, the sale included information on the historical use of the site, outline planning permissions and a fixed price remediation contract. Remediation was carried out and contamination contained on site, without the need for conventional dig and dump.

Royal Ordnance says that by linking remediation to the sale, Twigden had the benefit of a fixed price contract carried out by a main contractor and planning supervisor - Royal Ordnance Environmental Services Group - with detailed knowledge of the site and experience of cleaning up former explosive manufacturing sites. Royal Ordnance has also avoided any cashflow penalty by ensuring the site clean was finished before the sale.

The Waltham Abbey operation had been a research and development centre for explosives and propellant technology since the beginning of the century and acted as an overflow site to the much older Royal Gunpowder Mills to the north of the town, itself decontaminated between 1993 and 1996 and now a heritage site. In 1989, it was decided that UK research and development should be located with manufacturing and production activities, and the site was closed.

The main issue, says Royal Ordnance, was how to give future occupiers complete confidence that there was no risk remaining. The plan was agreed with the Environment Agency and Epping Forest District Council following a major site investigation.

Remediation in- cluded decontam- ination and demolition of more than 350 manu- facturing, storage and administrative build- ings totalling 48,000m2 and remedial earthworks removing some 400,000m3 of contaminated material. Two buildings of special significance have been dismantled and will be rebuilt at the Gunpowder Mills site.

Traditional dig and dump would have needed 45,000 lorries to remove the pollluted material and it was considered a poor and expensive environmenta solution. Instead, detailed site investigation was used to classify the materials.

Those exceeding agreed upper contamination limits (generally two to three times the open space thresholds) were buried in a 50,000m3 licensed containment landfill constructed on site, in a location with 'almost perfect geology'. Royal Ordnance says that the material is contaminated soil rather than toxic chemicals or industrial waste and that the landfill is licensed only for waste from the site itself.

Material above agreed public open space thresholds was placed above the water table to form landscape features on part of the site which is not being redeveloped, and capped with crushed arisings from the demolition plus a thick capping layer of clay.

Finally, some material was removed for confidence reasons. This was placed above the water table to form landscaping and capped with clay. The capped non-development areas will be sold on by Twigden to the Lee Valley Regional Park Authority to be restored as an extension to the park.

A further 600,000m3 of earthworks are now being finished. These include 'removing' a landscape feature known as Quinton Hill and will result in the site being almost level. It will provide the clay needed to cap the relocated contaminated materials and will be used as backfill on other areas of the site. Earthworks, landfill construction, excavation of nitrocellulose lagoons and dredging and reprofiling of a stream that was used for transporting explosives were carried out by J McArdle Contracts in a partnership contract with Royal Ordnance.

The project also included the relocation of grass snakes and bats to wooded areas on the southern edge of the site while remediation was carried out. These will be allowed to return naturally on completion of works.

And as part of the redevelopment scheme, French Kier Anglia is building a link road to the M25 through the site, which will also act as a bypass to Waltham Abbey town.

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