Turning the tide

After more than a decade of investigation and negotiation, a determined builder has moved a regulatory mountain to turn a polluted old shipyard into a residential complex and marina

Brownfield regeneration and the reuse of dredged materials are entwined in a groundworks, dredging and marine-construction project under way at Brightlingsea in Essex.

The former James and Stone Shipyard has been a blight on the town’s otherwise functional River Colne frontage for more than a decade. In its golden era, oyster and sprat fishing, and an excellent natural harbour, brought Brightlingsea to prominence. The yard produced scores of fishing boats, Thames barges and, during the war, military vessels at a time when environmental protection measures were non-existent.

The consequence has been a site polluted by oils, heavy metals and tributyl tins (TBTs).

A determined builder, Hampstead Homes (London), has bought the site after more than ten years of negotiation and investigation, and is now in the process of building a waterside residential complex with underground parking and a marina.

Previous applications had floundered on objections to the transport of heavily contaminated soils to distant (and expensive) landfill sites, and proposals to dump dredged materials from the required harbour area at sea.

Last autumn, Hampstead Homes appointed the Surrey-based Land and Water Group to develop and deliver a sustainable enabling works package as the first stage of a £25 million redevelopment scheme.

This required Land and Water to design a project and obtain consents from a wide array of regulators, led by the Marine Consenting Environment Unit of Defra.

Also requiring convincing of what can be done in an environmentally sound way in an intertidal habitat was the Environment Agency, the Harbour Commissioners, Tendring District Council, Brightlingsea Town Council, the Royal Society for the Protection of Birds, English Nature, Essex Wildlife, the Wildfowlers Association, and the local Oyster

Bed Association.

And all landward borders of the 2.5 hectare plot are occupied housing, and all seaward areas are protected habitat sites.

Within the Land and Water Group, Land and Water Remediation was to develop all aspects of the project relating to remediation of the heavily contaminated land, while Land and Water Services would preside over the design of marine works and conduct the dredging of the marina harbour.

The starting point was analysis of data from a geotechnical survey of the site, which had been conducted on behalf of the developer. Land and Water produced a 3D model of

the contamination based on the borehole results, chose an on-site soil-washing solution.

A flood-risk assessment carried out by the Environment Agency required the height of the site to be raised behind the sheet piling to cope with rising sea levels. The clean materials required to do this could be obtained by washing the contaminated soils on site, eliminating the need for lorry loads of soil to be removed from or delivered to the site.

This option also precluded the need to take contaminated soils to landfill. With the Landfill Directive substantially altering waste-disposal law last year, there are only six sites in the UK equipped to receive materials such as those at Brightlingsea, and the economics have swung in favour of reuse.

Hence, all the contaminated soils are screened and washed with a licensed mobile soil-washing plant, one of two such facilities in the UK. The skid-mounted equipment is brought to site on four articulated lorries and assembled using a mobile crane. The plant is capable of 350m3 per day throughput during the tightly restricted working hours.

The site is a beehive of activity. Excavators dig through sedimentary layers of oil-soaked soil while others separate metallic rubble and timber, and another delivers the dark, stinking raw material into the processing plant.

A mobile crushing plant among the cranes reduces large hard rubble to a size suitable for processing. Even old concrete ships, buried for decades under layers of sludge, have been pulled out and run through the crusher.

The plant itself is an L-shaped sequence of conveyors, separators, washing chambers, filters, water cleansing tanks and, finally, output belts taking finished product to storage piles where they await reuse. The plant is located on the only non-polluted portion of the site. Even the nearby Hampstead Homes sales office and show flat will have to be relocated so that the ground beneath it can be processed.

The processing plant has four separate outputs, all of which are reused on site. Course rubble, once clean, is crushed and used as fill. Washed shingle is used as a filter around the base of the sheet piling. Washed course sand is also used as fill. The final product is a lesser-contaminated fraction, which goes through a filter press and is chemically stabilised with cement to become a cake. This will be used to provide a base for the underground car parks.

The seaward side of the project is also well under way. Land and Water got the first of a series of consents between last November and the start of works in February 2005. At the time of EB going to press, the company was on track to delivering a remediated site with car park floors, three sheetpiled fingers for housing, and a dredged central harbour over to the builders by mid-November.

Again, the environmental benefits of the plan have won through in the consenting process. A sheet-piling design includes cathodic protection to combat accelerated low-water corrosion, while a low-level piled sill will hold water in the harbour at low tide.

Some 2,000 tons of sheetpiling was supplied and delivered to a scrap metal export yard on one chartered ship, eliminating the need for road deliveries by lorry. The piling is moved the short distance to site on flat-top barges. Piling works are being carried out by Haven Ports (Marine and Construction Management) and Commercial Marine Piling, which also provide two flat-top barges to move dredged material and additional manning on Land and Water’s pusher tugs.

Land and Water Services is dredging some 30,000m3 of non-contaminated alluvial clays and mud from the harbour area to a depth of 5m using a pontoon-mounted excavator featuring a self-developed visor, which closes over the bucket as it is lifted to minimise siltation. A special electronic dredging-control system has been supplied by Tower Hyrographics.

Dredging is restricted by consents to the incoming tide so that all sediment plume stays within the working basin. Dredged material is placed on to two flat-top barges and another two specially designed shallow-draft split-hopper barges built for Land and Water.

Working only on the high tide, the laden barges are pushed up the adjoining Brightlingsea Creek to three beneficial reuse areas licensed by the Environment Agency in a wildfowl sanctuary. Here another excavator removes the material and places it precisely to protect the eroded toe of sea-defence walls, while simultaneously constructing a new bird habitat.

With sites such as the old James and Stone Shipyard dotted in maritime locations throughout the UK and Europe, and the regulatory environment becoming ever more challenging, the Brightlingsea Marina project demonstrates that a carefully crafted and environmentally responsible development plan can still win the day.

As Land and Water’s Director James Maclean says: “This epitomises our way of working through complex regulatory issues. So many projects like this are defeated by legislation, but we have overcome a number of major obstacles to take this one forward.”

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