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Microbes do Skansk's dirty work


Skanska has already been praised for cleaning up contaminated land at Stratford but its use of biopiles, which accelerate natural processes, confirms its environmental approach, writes Russ Lynch

THERE'S an old adage that journalism is all about sifting through the dirt, but the expression is rarely taken literally.

Yet here I am on a cold and drizzly January day in Stratford, east London, ankle-deep in mud, staring at a 60,000 cu m heap of contaminated earth.

While it is not glamorous, it is worthy of attention.

What looks to the layman like a massive heap of earth is, in fact, the biggest ever bioremediation project in the country, attracting high-profile visitors such as Environment Agency chairman Sir John Harmon.

The site is Skanska Construction's Contract 230 for Union Railways (North), part of the second section of the Channel Tunnel Rail Link.

The contractor has the task of clearing up a total of 95,000 cu m of land contaminated by the two pollution hotspots on the Stratford site - a railway goods yard and a former gas works.

Due to the sheer volume of material involved, on-site remediation is the only economic option. Skanska calculated it would take 120,000 journeys in 7.5-tonne vehicles to remove the earth to the nearest landfill site nearly 15 miles away - the 'dig and dump' method.

It is difficult to imagine the local authority, Newham Borough Council, being overjoyed at this prospect.

Jennifer Clark, Skanska's environmental manager on Contract 230 says: 'Besides the cost of the operation, residents in the area would not have been too happy with that amount of vehicle activity.

'The council keeps a very close eye on things. When the wheelwash at the entrance broke down and there was some mud from the site getting on the road, vehicles were banned from leaving the site until it was fixed.'

The more conventional soil remediation technique is to lay out contaminated matter in lines known as 'windrows' and to drag a windrow turner up and down, aerating the soil with large blades.

But the cramped confines of the Stratford site do not afford the luxury of windrows; there simply is not the room. So Skanska brought on board a Canadian-owned company, Biogenie, in August 2001 to provide an alternative method.

The firm's £1.2 million solution works by shaping the land to be treated into two vast 'biopiles'. Pumps then draw oxygen through a vast network of piping - 8,000 m-worth in the 60,000 cu m of soil at Stratford - to accelerate the work of mother nature.

Paul Garrett, Biogenie's general manager, says: 'We are speeding up what would usually take up to 100 years into a 16-week process. Basically what we are doing is maximising the rate at which the billions of microorganisms present in the soil consume hydrocarbons.

'The speed of the process depends on the type of soil.

For example, gravelly soil will be treated more quickly than clay. Our assessment of the mixed soil composition at Stratford - clay, alluvials and gravel - was that it would be suited to biopiling.'

The first biopile was set up in October last year to treat matter extracted from the railway refuelling yard.

The results from this test will be analysed shortly. A second 35,000 cu m biopile is being built to remove the pollutants from the former gasworks site.

The average temperature of the biopile is a hot 50 deg C, with moisture levels kept at around 20 per cent for optimum efficiency.

Biogenie has agreed a target to reduce pollutants to one 10th of their original level at the end of the 16-week process. Skanska estimates that the biopiles will achieve this at less than a third of the cost of alternative methods.

The biopile also has a footprint of just 2,000 sq m - a quarter of the area required by the windrow method.

This is a significant factor on a site where space is at a premium.

When the majority of the pollutants have been consumed, the earth will be incorporated as fill into the lower levels of the land raise at Stratford, prior to the development of the area.

Ms Clark says: 'Along with Biogenie and two windrow firms, we also had a company tender for the job that wanted to use an 'E-Clay' system, where the contaminated soil is encased in a impermeable layer of clay.

'But this method is unproven and seems to be burying the problem rather than dealing with the pollutants. There is also the risk that a developer could come along later and pile through the protective layer.'

Using the biopile also eliminates the need for the specialist plant involved with windrows.

Mr Garrett adds: 'Using the windrows process, you would need to drag a windrow turner up and down to aerate the rows. Because of the size of the machinery, the rows would be limited in height to around 1.5 m.

'Besides, if the windrow turner was to develop a fault, it could take days to get a replacement on site. But you only need standard 360-degree excavators to manage the biopile.'

The Stratford biopile stands 2.5 m high. They can be built higher but, if the pile is too high, soil compaction near the base slows down the process.

Although the technology has been around for 20 years in Canada and the USA, the method is only just catching on over here.

Biogenie has already built a 12,000 cu m biopile for Edmund Nuttall on a remediation deal at Fulham gasworks in London and a 20,000 cu m structure for Mowlem at a former colliery site in Burnley. But the Stratford site represents the largest use of the technology so far in the UK.

Skanska has already won environmental plaudits at Stratford for clearing up over 500,000 litres of diesel fuel from the site. That the contractor has embraced biopiling confirms its conscientious approach. Just spare a thought for those billions of unpaid microscopic subbies beavering away 24 hours a day to clear the soil.

The environment manager

JENNIFER Clark is Skanska's environmental manager on Contract 230. This is not Ms Clark's first Channel Tunnel Rail Link contract as environmental manager - she also worked on Skanska's Contract 430 on the first section of the CTRL at Ashford in Kent.

She says: 'At Ashford there were vastly different challenges, such as river diversions.

There was some bioremediation, but not on the huge scale that we're doing here.'

CTRL Contract 230 SKANSKA began site work on the £105 million Stratford Box scheme, part of the Channel Tunnel Rail Link, in July 2001. The project involves the construction of a huge 1070 m underground box housing the new Stratford international station.

By the end of the deal, the contractor will have excavated 2.5 million cu m of earth to form the cut and cover box, which is 50 m wide and up to 31 m deep. The scheme is due for completion for client Union Railway (North) in mid-2005.

The excavated earth will raise the level of the land by around 9 m to allow future regeneration of the area (see below).

The two ends of the box were built first, so they could be handed over for the two bored tunnel deals, Contract 220 (Stratford to Gifford Road) and Contract 240 (Stratford to Barrington Road) last year.

A vision of the future

TWO HEAVYWEIGHT developers have joined forces for what will be one of the largest urban regeneration projects in Europe when the Stratford Channel Tunnel Rail Link station is completed.

London and Continental Railways chose Stanhope and Chelsfield as partners on a massive £3.5 billion development for the 60 ha site and the town centre last October.

The scheme will be phased over 15 years and includes 5,500 homes, 325,000 sq m of office space, and retail space spanning 140,000 sq m. More than 15,000 construction jobs will be created.

The project is seen as a key element in the development of the Thames Gateway and a way to address the imbalance between east and west London.

A Chelsfield spokesman said the development partners are planning to submit a planning application for the mammoth project to Newham Borough Council 'within the next few months'.