As pressure mounts to achieve the government’s housebuilding objectives, the effective regeneration of brownfield land is becoming increasingly important. Builder & Engineer takes a look at the challenges of regenerating contaminated land
THE Campaign to Protect Rural England (CPRE) recently analysed figures from 53 councils in the government’s brownfield register pilot scheme and found that more than 270,000 homes could be built on previously developed land across the country.
And with the government looking increasingly likely to miss its target of 160,000 new homes on publicly-owned land by 2020, Chancellor Philip Hammond and Sajid Javid MP recently announced plans to encourage housebuilding on brownfield sites “to get Britain building”.
Defined as land that has already been developed and having previously accommodated industrial, commercial or mining activities, Battersea Power Station and Nine Elms in central London are two of the high-profile brownfield sites already being redeveloped for residential use in the UK.
With 40 years in the industry and having completed its first remediation of Tipton Gas Works in the West Midlands in the 1980s, John McAuliffe, managing director of the McAuliffe Group, says these projects and the government’s plans to bring brownfield land back into use is fantastic news for the sector.
“Brownfield land offers UK housebuilders proximity to urban amenities and the opportunity to avoid using greenfield sites, so it’s time that these spaces were developed,” he says.
“The announcement by Hammond and Javid signals that the construction industry is now realising the value of regenerating smaller brownfield sites in towns and cities nationwide.”
But if the government’s aspirations on housing numbers is to be realised a more flexible approach to planning policies needs to be introduced.
“Planning on brownfield land can be extremely lengthy and complex given the legacy impact on the land,” explains Neil Williams, senior construction manager and head of remediation at St Modwen.
“The acquisition of brownfield land includes an initial purchase cost to acquire the land from former industrial land owners and a significant cost to prepare the land to a standard which is suitable for the intended uses.”
And, he explains, a one-size-fits-all approach regarding planning policy on brownfield sites (including community infrastructure levy, affordable housing, and S106 planning gain obligations) “can often put brownfield sites at a significant disadvantage when compared to greenfield sites.”
As expert geo-environmental consultants and remediation contractors, The LK Group provides integrated strategies to help housebuilders and land owners navigate the planning conditions attached to contaminated brownfield land and get regeneration projects moving.
Over the past 19 years, The LK Group has established a track record bringing brownfield land back into use, including cost-effectively cleaning sites that were previously thought to be undevelopable.
And technical director Dr Paul Quimby says that potential developers should be forearmed with as much site information as possible before engaging in any expensive regeneration projects.
“The remediation of land may not be as extensive or as expensive as housebuilders initially believe, and may not even be necessary at all. The key to understanding the level of work required is doing sufficient research up-front, so that developers don’t come across any unexpected costs further down the line,” he says.
Types of contamination
Before brownfield land can be redeveloped, sites need to be assessed by an environmental consultant who will test soil, groundwater and surface water for hazardous compounds and take steps to identify risks and liabilities.
The type of contamination depends on both the previous use of the site as well as the ground conditions and can include hydrocarbons on ex-petroleum oil refinery sites and pollutants like lead at former manufacturing sites.
And as contaminated land can present risk to human health, “re-use will normally require a degree of decontamination and clean up before a brownfield site can be deemed sufficiently safe to comply with current regulations,” explains McAuliffe.
Once the extent of contamination is established a range of remediation techniques can be employed to render the site suitable for use.
“In some instances, a simple clean soil capping system and physical barrier within the ground is sufficient to mitigate risks posed and allow development to continue,” says Alex Smiles, earth sciences director at civil and structural engineering specialist RoC Consulting.
However, on more heavily polluted sites, there may be a need to engage a specialist remediation contractor to excavate and clean the soils.
“In these instances, we would complete detailed mathematical modelling of the pollutants on site in order to identify the safe levels to which chemicals need to be reduced. This complex modelling is required to treat both soil and groundwater pollution,” explains Smiles.
The MLM Group has been actively involved with brownfield sites for nearly 20 years. Technical director Mark Henderson explains the two-stage approach to investigating contaminated land
Phase 1: Preliminary site investigation including desk study and site reconnaissance
The desk study involves collating all relevant available information including geological and historical mapping, carrying out environmental searches, checking online information held on the Environment Agency and British Geological Survey websites. In some cases, extended searches may be necessary such as for mining and petroleum storage licences.
Site reconnaissance involves a walkover survey noting features of interest such current site use, as fuel storage tanks, industrial process areas, chemical and waste storage, fly-tipping and visual evidence of contamination.
From these, we establish what sources of contamination might exist resulting from past or present site activities and consider how future site residents or groundwater quality receptors may become exposed to that contamination.
Phase 2: Intrusive on-site investigation
The scope of the ground investigation will be based on the findings in the first phase and targeted on features of concern, for example, underground storage tanks (USTs) discovered during the walkover which could have leaked fuel or an infilled pond shown on historical mapping which could be emitting ground gases.
Site work typically involves putting down boreholes or trial pits to observe ground conditions and take soil samples. At some sites, we will install monitoring wells and make return visits to measure ground gases or take water samples. Samples will then be tested for a range of contaminants according to what the site was used for and what was found in the ground.
The results of testing and monitoring are compared with screening levels, which might indicate any risk to human health or the environment and require remediation for safe development.
Horwich Locomotive Works, Bolton
Located on the former Horwich Locomotive Works, and covering an area in excess of 80 hectares, the £260 million Rivington Chase development in Bolton is one of the largest brownfield regeneration schemes in the North West.
RoC Consulting was appointed to undertake a site-wide first phase ground investigation comprising 160 boreholes to establish baseline conditions as well as a remediation strategy to increase the developable area.
The site has been subject to over 130 years of industrial activity with numerous sources of contamination but following a review of the site investigations works, it was noted that, although containing numerous contamination hotspots, the made ground depth in the area of the former Loco Works buildings was relatively shallow and workable.
RoC Consulting therefore recommended conventional processes such as soil washing and bio remediation, meaning the made ground material can be re-used as additional capping across the adjacent works tip.
By increasing the thickness of soil capping, the works tip can be brought into use, either as public realm space or housing.
In addition, by removing made ground in the area around the existing works buildings, RoC Consulting will “design out” numerous abnormal features from the development plots on this portion of the site, by specifying specialist foundations, gas protection measures, chemically resistant pipe work and clean soil capping systems for garden plots.
As part of the brief, a site-wide “cut and fill” exercise was also undertaken using specialist 3D modelling software PDS Volumetrics and RoC Consulting is currently undertaking more detailed design of supplementary ground investigation to further characterise site conditions and remedial works.
Coed Darcy, South Wales
A 25-year project to regenerate the industrial legacy left behind by the former BP Llandarcy oil refinery in Neath Port Talbot is well underway.
When completed the £1.2 billion Coed Darcy project will consist of 4,000 new homes, 40,000 sq ft of retail and leisure space, three primary schools and 85,000 sq ft of additional commercial space.
Established as an oil refinery in South Wales in 1918, Llandarcy became one of the largest employers in the region but, by the time it closed in 1998 the plant had also become one of the most polluted sites in Europe with 1,060 acres of land heavily polluted with the by-products of 70 years intense production in processing hydrocarbons.
In 2008, regeneration specialists St Modwen brought in specialists Celtic, Hydrock and Hawk, as well as WS Atkins and introduced ground-breaking technologies to transform the site.
Heavy oils that had sunk to the bottom of ponds and lagoons, forming a deep layer of sludge, received a de-watering treatment.
This left a more concentrated material with a consistency like peat, to which the team added “cement bypass dust”, a waste product of cement manufacturing.
The end result was a structural material which could be used to build road embankments for Coed Darcy without having to bring in construction materials.
The lighter hydrocarbons, which formed a top layer on open ponds, reservoirs and shallow groundwater, were removed with specialist mops for recycling into oil products.
Earth that was less heavily contaminated but still in need of cleaning was subject to bioremediation, where natural soil bacteria broke down the hydrocarbons into carbon dioxide and water.
To introduce the oxygen needed for this process, the ground was ploughed up to form rows of earth that could be aerated further by turning them over every two or three weeks.
Despite the industrial activity, Llandarcy retained plenty of wildlife and the wetland now provides a natural source of native plants and animals to spread back across the site.