London Olympics: Cleaning up highly contaminated land
With a higher budget than any of the venues, the Olympic enabling works and remediation project is site clearance on a massive scale. Andrea Klettner describes how BAM Nuttall and Morrison cleaned up some of the most contaminated land in modern British construction.

Mankind has inhabited East London's Lea Valley since Roman times, with the area going through vast changes as it encompassed life as a trade route, industrial centre and now its preparation to become the home of the 2012 London Olympic Games.

But the area's rich history has contributed to making the 246ha site one of the most contaminated in modern British construction, resulting in a clean-up operation of unprecedented size.

Olympic Delivery Authority (ODA) director of infrastructure and utilities Simon Wright explains the scale of the job 'Altogether the enabling works and remediation have a higher budget than any of the venues, that shows you just how big this project is.'

The enabling works themselves have a budget of £325m, with the total site preparation and related infrastructure costing £1.7bn.

Because of the size of the site, the ODA decided to split the main enabling works job, which focuses mainly on site clearance and remediation, into two.
'It's all about risk mitigation,' says Wright. 'You have to remember that in 2006 the market was very different and at the time we were worried about a single firm not having enough resources.'

In 2006, Edmund Nuttall (now BAM Nuttall) and Morrison won the demolition and remediation contracts for the site - south and north respectively - from the London Development Authority.

From the beginning the job proved to be a challenge, starting with the geography of the Lea Valley. As an industrial river basin it is criss-crossed by various waterways, railways and the A12 artery road linking London and Essex.

BAM Nuttall engineering manager Stephen Deeble says: 'There are lots of impenetrable boundaries on this site, making about eight smaller island sites. 'When we first started there was only one bridge, so one of the first things we had to do after making the site secure was to build three more bridges to allow us to move materials around, and for other site users to get around more easily.'

Site surveys
Next came a series of site surveys, helping to determine where the re-usable materials were to be found.

Morrison construction manager Aaron Evans says: 'We had a target of re-using 90% of the waste from the site. We don't usually get such high targets, or if we do they go out the window because of budget constraints. 'But for the Olympics we've been strict with sticking to them.'

Before any buildings could be demolished the asbestos was removed and taken away from the site, leaving all other materials to be re-used or recycled.

'The metal was all brought for recycling,' explains Deeble.'"The masonry slabs were lifted, crushed, graded, screened and tested for content - to be made into engineering products.'
The majority of the re-used masonry was turned into load bearing fills to be used across the site including in temporary and permanent roads, piling mats and fill below water level.

But the biggest job for both the southern and northern parts of the park was still to come with the remediation phase, with each area bringing its own challenges.

BAM Nuttall was faced with strict deadlines, having both the main Olympic stadium and the Aquatic Centre on their half of the site, while in the north Morrison had to contest with an unregulated Victorian landfill.

'The excavation around the Aquatic Centre was one of the biggest challenges,' admits Deeble. 'The site had been home to noxious industries including tanneries and motor breakers since the late 18th century and as it was outside the old border of London it was not subject to any kind of environmental constraints.'

The soil contained inorganic metals, petroleum hydrocarbons and volatile organic compounds. 'The soil was washed and when it was too fine to wash we bioremidiated it,' says Deeble.'"Around the main stadium the majority of the soil was stabilised using chemicals.

'As you can imagine, the volume of material that needed moving was immense and we had to find temporary storage for the safe material.'

Working together with Morrison did help here - BAM was able to bring material to the northern part of the site to be stored for future use, with plant mainly supplied by sub-contractor Hawk.

Deeble continues: 'This led us to have the site for the Aquatic Centre ready on time, and for the main stadium we were early, allowing construction to start three months ahead of schedule.'

Thorium barrels
Meanwhile, a few kilometres to the north Morrison was contesting with the Victorian landfill, which was rumoured to contain thorium barrels.
'The tip made up around a quarter of our site and it was full of historic waste,' says Evans.

A 10m-deep archaeological trench was dug around the edge of the site. One of the most exciting things found by the team was an old road, with evidence of an old mill.

'We also found a cobbled street, that was excavated and will be used to build a new road in the Olympic park,' reveals Evans.

The soil from the tip was also re-used, following a complex sorting procedure. First, the finer soils were screened out and the waste was handpicked. Because of the age of the tip the majority of the waste came from wood, leather and material sources, allowing it to be burned.

Oversized items including bottles, bricks and concrete was crushed and re-used around the park for temporary works such as roads and piling mats. During the process all precautions were taken to ensure the site remained safe in the event that thorium was found, but luckily the soil contained no radioactive material.

Throughout the project both teams have kept a close eye on dust control. The sheer size of the site, and the fact that it is surrounded by residential areas, meant that local councils enforced strict policies when it came to dust. "We started setting up contact with the Environment Agency in 2006 and prepared a code of practice that was incorporated into the planning process," explains Deeble. 'Once we started with remediation it helped that the largest muckshift we did, for the main stadium, began in the winter when it's easier for the soil to retain water.

'We also ensure that the stockpiles were shaped smoothly so we didn't get wind shear, and the long-term piles are sprayed with sealant.' Three years on from the start of the job, the remediation is now largely finished - the teams have handed over some 285 sites out of 350. Now BAM Nuttall and Morrison are now working with other contractors on the site to ensure their soil is up to standard.

Evans explains:'"We assess arisings that come from other construction projects, then make them into fill materials. There has definitely been a change in emphasis of our role, we're seeing that materials are being re-used several times over.'

Cleaning up the groundwater
The 2012 Olympic site has become the location of an innovative trial to get rid of ammonia in contaminated groundwater.

Single-celled micro-organisms known as archaea, which occur naturally in water and degrade ammonia in order to survive, have been encouraged to breed on the site.

'We have produced a bioreactor so they can breed more rapidly and extract ammonia from the groundwater,' explains Deeble. 'So far they have generated a notable improvement in ammonia levels, and everyone knows that ammonia is notoriously hard to get rid of.'

The water is also pumped from the ground to be treated. Some contaminants can be dissolved and removed, while others are eliminated through chemical oxidation.

Learning from the project
Brownfield site development is becoming increasingly more popular in the UK, especially with the Government's ambitious housing targets.

ODA director of utilities and infrastructure Simon Wright believes the huge remediation job at the East London Olympic site can serve as a blueprint for future projects, including the Thames Gateway.

He says: 'If we are going to redevelop urban areas and avoid building on greenfield sites, then we will certainly be dealing with contaminated land. And the efficiency with which you can make such land fit for re-use is vital.'

Article courtesy of Contract Journal - september 2009

Further Info
Peter Bishop - Head of Public Relations & Corporate Communication
BAM Nuttall Limited
St James House, Knoll Road, Camberley,
Surrey GU15 3XW
Tel: 01276 63484
Fax:01276 66060
peter.bishop@bamnuttall.co.uk