The effective regeneration of brownfield land is becoming increasingly important as pressure mounts to meet the government’s housebuilding targets. Builder & Engineer examines the difficulties of regenerating contaminated land.
THE Campaign to Protect Rural England (CPRE) recently analysed data from 53 councils participating in the government’s brownfield register pilot scheme and discovered that more than 270,000 homes could be built across the country on previously developed land.
And, with the government looking increasingly likely to fall short of 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 in order “to get Britain building.”
Battersea Power Station and Nine Elms in central London are two high-profile brownfield sites that are already being redeveloped for residential use in the UK. Brownfield sites are defined as land that has already been developed and has previously housed industrial, commercial, or mining activities.
With 40 years of experience 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 repurpose brownfield land are fantastic news for the sector.
“Brownfield land provides UK housebuilders with proximity to urban amenities as well as the opportunity to avoid using greenfield sites, so it’s past time that these spaces were developed,” he says.
“Hammond and Javid’s announcement shows that the construction industry is finally realising the value of regenerating smaller brownfield sites in towns and cities across the country.”
However, if the government’s housing targets are to be met, a more flexible approach to planning policies must be implemented.
“Because of the legacy impact on the land, planning on brownfield land can be extremely lengthy and complex,” explains Neil Williams, senior construction manager and head of remediation at St Modwen.
“Brownfield land acquisition includes an initial purchase cost to acquire the land from former industrial land owners as well as a significant cost to prepare the land to a standard suitable for the intended uses.”
And, he adds, a one-size-fits-all approach to brownfield planning policy (including community infrastructure levy, affordable housing, and S106 planning gain obligations) “can frequently put brownfield sites at a significant disadvantage when compared to greenfield sites.”
The LK Group, as expert geo-environmental consultants and remediation contractors, offers integrated strategies to assist housebuilders and land owners in navigating the planning conditions associated with contaminated brownfield land and moving regeneration projects forward.
Over the past 19 years, The LK Group has built a reputation for repurposing brownfield land, including cleaning sites that were previously thought to be undevelopable.
And, according to technical director Dr. Paul Quimby, potential developers should be armed with as much site information as possible before embarking on any costly regeneration projects.
“Land remediation may not be as extensive or costly as homebuilders initially believe, and it may not even be necessary at all.” “The key to understanding the level of work required is conducting adequate research up front, so that developers do not encounter any unexpected costs later on,” he says.
Before brownfield land can be redeveloped, it must be evaluated by an environmental consultant, who will test soil, groundwater, and surface water for hazardous compounds and identify risks and liabilities.
The type of contamination is determined by both the previous use of the site and the ground conditions, and can include hydrocarbons on ex-petroleum oil refinery sites and pollutants such as lead on former manufacturing sites.
Furthermore, because contaminated land can endanger 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,” McAuliffe explains.
Once the extent of contamination is determined, a variety of remediation techniques can be used to make the site safe 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 firm RoC Consulting.
However, on more heavily polluted sites, a specialist remediation contractor may be required to excavate and clean the soils.
“In these cases, we would conduct detailed mathematical modelling of the pollutants on-site in order to determine the safe levels to which chemicals must be reduced.” Smiles explains that “complex modelling is required to treat both soil and groundwater pollution.”
The investigation procedure
For nearly two decades, the MLM Group has been actively involved with brownfield sites. Mark Henderson, technical director, explains the two-stage approach to investigating contaminated land.
Phase 1: Preliminary site investigation, which includes desk research and on-site reconnaissance.
The desk study entails gathering all relevant available information, including geological and historical mapping, conducting environmental searches, and double-checking online information on the Environment Agency and British Geological Survey websites. Extensive searches may be required in some cases, such as for mining and petroleum storage licences.
A walkover survey is conducted to identify features of interest such as current site use, such as fuel storage tanks, industrial process areas, chemical and waste storage, fly-tipping, and visual evidence of contamination.
Based on these, we determine what sources of contamination may exist as a result of past or current site activities, and we consider how future site residents or groundwater quality receptors may be exposed to that contamination.
Phase 2: On-site investigation that is intrusive.
The scope of the ground investigation will be based on the findings of the first phase and will be focused on areas of concern, such as underground storage tanks (USTs) discovered during the walkover that may have leaked fuel or an infilled pond shown on historical mapping that may be emitting ground gases.
Boreholes or trial pits are typically installed on the job site to observe ground conditions and collect soil samples. We will install monitoring wells at some sites and return to measure ground gases or collect water samples. Following that, samples will be tested for a variety of contaminants based on what the site was used for and what was discovered in the ground.
Testing and monitoring results are compared to screening levels, which may indicate any risk to human health or the environment and necessitate remediation for safe development.
STUDY OF A CASE
Bolton’s Horwich Locomotive Works
The £260 million Rivington Chase development in Bolton is one of the largest brownfield regeneration schemes in the North West, covering an area of more than 80 hectares on the former Horwich Locomotive Works.
RoC Consulting was hired to conduct a site-wide first phase ground investigation that included 160 boreholes to establish baseline conditions and a remediation strategy to increase the developable area.
The site has been subjected to over 130 years of industrial activity, with numerous sources of contamination, but a review of the site investigation works revealed that, despite the presence of numerous contamination hotspots, the made ground depth in the area of the former Loco Works buildings was relatively shallow and workable.
As a result, RoC Consulting recommended traditional processes such as soil washing and bio remediation, which means that the created ground material can be reused as additional capping across the adjacent works tip.
The works tip can be used as public realm space or housing by increasing the thickness of the soil capping.
Furthermore, by removing made ground 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.
A site-wide “cut and fill” exercise was also carried out as part of the brief, using specialist 3D modelling software PDS Volumetrics, and RoC Consulting is currently carrying out more detailed design of supplementary ground investigation to further characterise site conditions and remedial works.
South Wales, Coed Darcy
A 25-year project is well underway in Neath Port Talbot to regenerate the industrial legacy left behind by the former BP Llandarcy oil refinery.
The £1.2 billion Coed Darcy project will include 4,000 new homes, 40,000 square feet of retail and leisure space, three primary schools, and 85,000 square feet of additional commercial space when completed.
Llandarcy, established as an oil refinery in South Wales in 1918, became one of the region’s largest employers, but by the time it closed in 1998, it had also become one of Europe’s most polluted sites, with 1,060 acres of land heavily polluted with the by-products of 70 years of intensive production in processing hydrocarbons.
St Modwen, a regeneration specialist, brought in Celtic, Hydrock, and Hawk, as well as WS Atkins, in 2008, and introduced ground-breaking technologies to transform the site.
Heavy oils that had settled to the bottom of ponds and lagoons, forming a thick layer of sludge, were de-watered.
This resulted in a more concentrated material with a peat-like consistency, to which the team added “cement bypass dust,” a byproduct of cement manufacturing.
The end result was a structural material that could be used to construct road embankments for Coed Darcy without the need for construction materials.
Lighter hydrocarbons that formed a top layer on open ponds, reservoirs, and shallow groundwater were removed with specialised mops and recycled into oil products.
Bioremediation was used on earth that was less heavily contaminated but still needed cleaning. Natural soil bacteria broke down the hydrocarbons into carbon dioxide and water.
The ground was ploughed up to form rows of earth that could be aerated further by turning them over every two or three weeks to introduce the oxygen required for this process.
Despite the industrial activity, Llandarcy has a thriving wildlife population, and the wetland now serves as a natural source of native plants and animals for reintroduction to the site.