Fast tracked remediation reclaims shipyard site
The twin themes of brownfield site regeneration in maritime environments and the beneficial re-use of dredged materials are being entwined at an innovative and significant groundworks, dredging and marine construction project currently under way at Brightlingsea in Essex
The former James and Stone Shipyard has been a blight on the Essex town's otherwise functional River Colne frontage for more than a decade. The legacy of a golden era when oyster and sprat fishing combined with an excellent natural harbour to bring 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 21st century consequence has been a site so polluted by oils, heavy metals and TBTs that a determined builder, Hampstead Homes (London) Ltd, has purchased after more than ten years of negotiation and investigative works, and is now in the process of constructing a waterside residential complex, with amenities such as underground parking and a fully serviced marina. Previous applications had foundered 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 Land & Water Group to develop and deliver a sustainable enabling works package as the first stage of a £25 million redevelopment scheme. This required Land & Water to design a project and obtain consents from a formidable array of regulators, led by the Marine Consenting Environment Unit (MCEU) of the British Government's Department for Environment, Food and Rural Affairs (DEFRA).
Also requiring convincing of what can be done in an environmentally sound way in an intertidal habitat was the UK 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. As if that were not enough, all landward borders of the 2.5 hectare plot are occupied housing and all seaward areas are protected habitat sites.
Within the Land & Water Group, Land & Water Remediation was tasked with developing all aspects of the project relating to remediation of the heavily contaminated land while Land & 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 & Water produced a 3D model of the contamination based on the borehole results and elected to use an on-site soil washing solution. A Flood Risk Assessment conducted by the Environment Agency required the height of the site to be raised behind the sheet piling in order to accommodate rising sea levels.
The clean materials required to do this could be obtained by washing the contaminated soils on site, eliminating the requirement for lorry loads of soil to be removed from or delivered to the site. This option also precluded the requirement 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 re-use.
Hence, 100% of the contaminated soils on site are being screened and washed using Land & Water's licensed mobile soil washing plant, one of only 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 that are a condition of the consent.
On this highly active site, excavators tackle a range of tasks, digging through sedimentary layers of oil soaked soil, separating metallic rubble and timber and feeding the polluted raw material into a processing plant. A mobile crushing plant amongst 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 various types of finished product to storage piles where they await beneficial re-use. The plant is located on what has been determined to be 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 re-used 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" which will be used
to provide a base for the underground car parks.
The seaward side of the project is also well under Seway.
Having obtained the first of a series of consents in the remarkably short period between last November and the start of works in February, Land & Water is on track to deliver a fully remediated site with car park floors, three sheetpiled fingers for housing and a dredged central harbour, 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 ALWC, 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 nearby scrap metal export yard on one chartered ship, again eliminating the need for numerous 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 are also providing two flat top barges to move dredged material and additional manning on Land & Water's pusher tugs.
Land & Water Services is dredging some 30,000 m3 of non-contaminated alluvial clays and mud from the harbour area to a depth of five metres 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 remains 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 & Water. Working only on the high tide, the laden barges are pushed up the adjoining Brightlingsea Creek to three beneficial re-use areas licensed by the Environment Agency in a wildfowl sanctuary. Here another Land & Water excavator removes the material and places it precisely to protect the eroded toe of sea defence walls while simultaneously constructing a new bird habitat.
Pointer to the future
Many sites such as the old James and Stone Shipyard located around the coasts of Britain and Europe are becoming subject to an increasingly stringent regulatory environment, however, the Brightlingsea Marina project demonstrates that a carefully planned and environmentally responsible development plan can succeed.
According to Land & Water's Director, James Maclean, "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."