Hauxton clean-up shows what can be achieved

Tackling the legacy of industrial pollution can be a lengthy process, but remediation of Bayer CropScience’s former site in Hauxton, Cambridgeshire, is proceeding apace. The multi-million pound project will deliver 8.5 hectares of prime development land, finds David Carr

Hauxton site, courtesy of VertaseThe past two years have not been a boom time for contaminated land remediation. The recession blunted the appetite for brownfield development and many contaminated sites have simply remained dormant (ENDS Report 408, pp 5-6).

But an 8.5-hectare site near Hauxton, Cambridgeshire, is going against the grain. It was host to Bayer CropScience’s plant, where the company and its predecessors – Fisons, Schering Agrochemicals, Agrevo and Aventis CropScience – had made and stored agrochemicals since the 1940s (ENDS Report 341, p 29).

Now it is being remediated. Works started in March and are set for completion in September 2011.

Bayer acquired the site and Aventis CropScience in 2002. It operated there until 2004, when pesticides and herbicides manufacturing ceased, leaving a legacy of soil and groundwater contamination.

Contamination was recorded as early as 1965. In 1972, it was discovered in an adjacent watercourse, the Riddy Brook, and again in the late 1980s. The water was both a receptor of and pathway for the contaminants.

 But it was only detailed investigations, undertaken by consultants Enviros and Atkins in 2005 and 2006, that confirmed the presence of multiple contaminants on the site. The effectiveness of a protective barrier installed in 1974 was a concern.

In 2003, South Cambridgeshire District Council determined the site as contaminated land, under part 2A of the Environmental Protection Act 1990. It was designated a special site , making it the responsibility of the Environment Agency.

Hauxton has several distinct characteristics. It is large, its rural location distinguishes it from its typically urban peers and it has a fairly complex, unique mix of contaminants.

It was also one of the first special sites to be designated. By March 2007, 35 such sites had been designated, but only five had been successfully remediated. Progress on part 2A sites as a whole has been painfully slow (ENDS Report 410, pp 36-39).

Several problems have blunted the regime’s effectiveness, but this site illustrates how they can be overcome. Claire Sproats, the district council’s current contaminated land officer, says: “Part 2A gave us a method of dealing with it.” For Hauxton, the question was “not whether it would be remediated, but how”.

Taking responsibility

Liability clearly lay with Bayer, but developer Harrow Estates acquired the site in 2005 with a view to building a housing and mixed-use development.

“Bayer wanted to sell it to someone who could fulfil the part 2A obligations and take the liability away,” explains Mark Nicholls, technical director at Harrow Estates.

But why take on such a complex site and the liability for it? Mr Nicholls says: “It’s attractive to us because it’s what we do. We have a track record of similar sites. It offers a fantastic opportunity. It’s a rural site, yet close to Cambridge, in a prime location close to the A10 and M11 corridor.”

Ownership passed to property group Bridgmere, with Harrow becoming the managing agent. But Hauxton is the most challenging site Harrow has tackled and redeveloping it for housing introduced a possible threat to human health.

Planning permission was only considered subject to the site being suitably remediated. Harrow Estates made two planning applications: one for the remediation and the other for the development.

Given the site’s complexity, “there were very contentious issues involved”, says Mr Nicholls. The original remediation planning consent was granted, then quashed by agreement after a neighbouring farmer challenged it. South Cambridgeshire District Council conceded that it did not have enough information available when it decided whether an environmental impact assessment (EIA) was required. An EIA was later undertaken and the planning application resubmitted. 

But the five years that passed from 2005 until remediation work began was, Mr Nicholls claims, something of a bonus: “It gave us the luxury of time, allowing us to do things properly and fully.”

Atkins was appointed as a consultant, detailed site investigations were carried out, a strategy developed, works tendered and plans enacted. Site demolition works ended in June 2008, paving the way for remediation and redevelopment.

This finally got the green light in February 2010, when planning consents were granted for a residential and mixed-use development, subject to remediation being achieved to a sufficiently high standard.

“We’ve not had a site that has taken so long to get to this point and because it’s a part 2A site, it’s been quite a process. It has been an interesting journey and quite a learning curve,” says Mr Nicholls.

Sheffield-based contractor Vertase FLI was appointed to undertake the remediation. Steve Edgar, the firm’s project director for Hauxton, says that by March it was “well prepared, having looked at the site data, considered Atkins’ findings and the risks posed to water and health”.

Investigations had found contamination scattered across the site following decades of agrochemicals production. A number of ‘hot-spots’ were identified, alongside less-contaminated areas. There were 23 key contaminants of concern identified, posing the greatest threat to human and water health, and these were mostly dissolved within soils and groundwater.

Comprising mostly hydrocarbons used in the manufacturing processes, alongside finished and intermediate agrochemicals and break-down products, they included pesticides, herbicides, toluene, tri- and tetra-chloroethene and tri-methylbenzene.

Pilot trials and laboratory tests were used to establish the optimal treatment methods. A single, site-wide remediation technique was rejected because of the variety of contaminants and soil types. Some are clay-like, others more granular.

Covered odorous soils, courtesy of VertaseInstead, a treatment process was agreed with ‘ex-situ’ bioremediation as the primary technique. This involves excavating soils and treating them elsewhere on-site using physical and biological processes.

A detailed strategy was developed and a method statement prepared, showing how the remediation would be delivered, attaining a standard suitable for housing.

“We decided to excavate the whole site and identify all the problems and contamination sources,” says Mr Edgar. “This drove the whole strategy.”

The aim is to remove all uncertainty surrounding the soils and groundwater through excavation, characterisation and treatment. Only when this is achieved, confirmed through laboratory analysis and the soils returned will the site be ready for redevelopment.

This must all be done within the terms of the planning consent and an environmental permit, issued and regulated by the agency.

The permit covers the specific activities undertaken and allows for on-site treatment of contaminated materials. The permit also specifies monitoring requirements and details the abatement measures that must be complied with to prevent pollution and potential harm to human health.

Levering experience

The Hauxton remediation is a major project but Vertase and Harrow can draw on their experience in tackling similar sites for residential development, such as a former chemical works and tar distillery in Cadishead, Salford.

Located above an aquifer, Cadishead also had a long history of industrial activity. Chemicals, including solvents, hydrocarbons, heavy oil fractions and tar distillation products were made there from about 1900, leaving a legacy of contamination.

The soil and groundwater was contaminated with benzene, toluene, ethylbenzene, xylenes, polycyclic aromatic hydrocarbons (PAHs), diesel, general hydrocarbons and tar in both solid and liquid states.

Harrow Estates proposed to develop the site for housing and contracted Vertase to undertake the remediation. The tar contamination was removed, but all other soils were treated on-site, through biological treatment. After being excavated, screened, crushed, segregated and placed into windrows, more than 100,000 cubic metres of soils were treated through ex-situ bio-remediation.

And like Hauxton, the Cadishead site posed a risk to ground­water. A temporary barrier was installed to prevent contaminants migrating and to collect groundwater. The site was drained and the effluent treated on-site.

At Hauxton, a spring start on the remediation was favoured to minimise exposure to bad weather. The work plan was started and equipment installed. Some 170,000m3 of soils will be handled, dug from depths of up to seven metres.

Materials began to go though the treatment process from 15 March, with a number of techniques being deployed. They include simple concrete crushing and sorting, soil conditioning and screening for reuse, ex-situ bio-treatment, force-ventilated bio-treatment and chemical oxidation.

Materials are assessed for contamination as they are uncovered. Soils are separated using mechanical screens or sieves and shredders, breaking them up so they can be treated. The contaminants’ nature and their host soils dictate where materials are directed to for on-site treatment.

The bio-treatments involve natural processes. Once excavated and exposed to the air, microorganisms in the soils serve to degrade the contaminants to harmless by-products. Where soils permit, the process is enhanced by using forced-air ventilation, with the by-products being vented to the atmosphere following appropriate treatment via an air biofilter.

Following treatment, soils are sampled to find out if the treatments have been effective. The goal is to reuse most soils on-site to avoid large-scale transfer of contaminated materials and reduce costs.

Hauxton’s groundwater is also being treated at a dedicated plant across the A10. This has long been used to treat the site’s groundwater, but has been modified to improve its efficiency. Once treated, water is discharged into the river Cam.

So far, so good. But a number of other issues have had to be tackled as remediation proceeds. Chief among these is reducing the incidence of odours, stemming from the release of volatile organic compounds (VOCs).

A number of odour complaints have come from people living nearby. The local MP and health secretary, Andrew Lawnsley, visited the site in June and conveyed their concerns to the agency. They are being addressed through various management techniques and an on-site deodoriser system.

Odorous soil beds are kept covered and the most potentially odorous activities are planned around wind and weather conditions.

Meanwhile, nozzles placed around the site’s perimeter spray a fine water mist and a dilute, non-toxic deodoriser akin to a domestic air-freshener.

Air quality is being monitored at fixed locations, in response to complaints, and at random points. Results are forwarded to the agency and the council, with the Health Protection Agency (HPA) helping to interpret the findings. It has raised no toxicology concerns from the odours and emissions emanating from the site.

In all, the remediation process should take about 80 weeks and be completed by September 2011. The site will then be monitored for at least six months and the groundwater tested. Only when it receives a clean bill of health will the site be deemed fit for development. A protective membrane will not be needed once the groundwater is remediated.

Several other stakeholders are active alongside Harrow and Vertase, on-site and further afield, providing advice, monitoring progress and ensuring compliance. Atkins is supervising Vertase. Acting as the on-site environmental consultant, it ensures independent validation and monitoring of the work.

Hauxton is also being visited frequently by the regulators: South Cambridgeshire District Council and the Environment Agency. The council is responsible for enforcing the planning conditions and working with the agency in addressing local residents’ concerns.

The agency must ensure that the terms of the environmental permit are fulfilled and act as first port of call for responding to on-site environmental incidents, such as excessive emissions or odour problems.

“We’ve long been involved with the site,” says Kevin Rutterford of the agency’s Anglian region, who has responsibility for assessing compliance and enforcing permits. “The agency and its predecessors regulated production there and discharges from it. Now we’re back, ensuring compliance with its remediation.”

The regulators are also being assisted by the HPA and the NHS, who are providing scientific, toxicological analysis and data monitoring services.

Digger excavating soil on the Hauxton site, courtesy of VertaseCoordination and communication

The importance of effective coordination and communication between parties is a key lesson being learned at Hauxton. It is proving crucial in ensuring the project’s smooth progress. (Please also see this article on the revised guidance on communicating land risks).

“It’s a complex process, but it is working well and communications are good,” says Mr Edgar. Teleconferencing has been used to ensure all parties are regularly kept informed.

“Hauxton is a good example of many people and organisations successfully working together,” says the council’s Mrs Sproats. “The importance of good working relationships can not be understated.”

But wider public communication has also been important, particularly in the post-Corby case era (ENDS Report 415, pp 20-21). Media coverage of the legal action which followed the badly managed Corby steelworks clean-up sparked concerns among some locals who knew the Hauxton site was in line for remediation.

They were unfounded, given the high standards set for Hauxton. Most local people broadly favoured the site’s redevelopment, but the developers still wanted to keep them informed.

A communications strategy for all parties was drawn up, aimed at giving the public a forum to have their concerns aired and addressed. Comprising drop-in sessions, letter drops to residents, notice boards and question-and-answer sessions, the strategy has helped allay local concerns. Detailed information has also been made available on the council’s website.

Getting the communications strategy right was key. If provided with too little information, the public may have been ill-informed. Too much, and needless concerns could have been exacerbated.

“It’s taken a lot of work, but most people are now okay about the project,” says Mrs Sproats.

Indeed, five years on from Harrow’s acquisition of the site, the project now seems to be heading towards a successful conclusion after a long and complex process.

“Hauxton shows that you can reclaim large sites in sustainable ways and bring them back into beneficial use,” says Vertase’s Mr Edgar. If that sounds like a simple process, it certainly has not been so.

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