Building homes on used land

Pal Syms and Peter Knight

This study examines the redevelopment process and the problems faced by the developers of ten sites where housing is being built on previously developed land.

Summary

Summary

The areas of derelict and vacant land found in many towns and cities are a legacy of Britain's industrial past. All too often this land is forgotten, 'unused and unloved', possibly contaminated or suffering from other problems, such as inadequate access or lack of service infrastructure. In spite of these drawbacks this 'previously developed' land may be in locations where people want to live, close to employment and social amenities. It is also Government policy that this land should be reused for housing, in preference to greenfield development. Researchers from Sheffield Hallam University have examined the redevelopment process and the problems faced by the developers of ten sites. The study found:

  • Relationships between housing developers and local authorities can be strained by different objectives in reusing 'previously developed' land.
  • The historic study of land use forms an essential part of a comprehensive site investigation.
  • There are many different remediation options: selecting the most appropriate options will often have a significant impact on the viability of a housing development. For most of the developers on the case study sites, cost and speed of completion were the main factors behind selecting which methods to use.
  • Providing factually correct and readily assimilated information on past uses, site investigations and remediation works does not appear to deter purchasers and tenants.
  • The researchers conclude that validation of the site preparation work by an appropriately qualified person would ensure compliance with the remediation strategy and achievement of its goals. 

Introduction

The brief for this research was to look at how Government policies were applied in practice by housing developers and the problems they faced in reusing land, by examining a range of case studies. 

Government policy is that most land contamination should be dealt with through the planning system, except where 'significant harm' or pollution of controlled waters is being or is likely to be caused. In such cases the regulators may take action unconnected to the planning regime under Part IIA of the Environmental Protection Act 1990 (the 'contaminated land' legislation).

Development problems

The case studies demonstrate that contamination is an important issue that needs to be addressed at an early stage and show that the selection of suitable consultants and contractors is extremely important. One of the case studies illustrates how extensive contamination may be missed by an inadequate site investigation or one that is hindered by the presence of existing buildings and plant. 

Site access is an important consideration; without adequate access the site is unlikely to be developable, even though it may be possible to resolve physical ground condition problems. In the case of a former cotton mill and bleach works, for example, problems with access contributed to the development being abandoned. Related to access problems are issues such as the closure of existing streets or the diversion of public footpaths, so as to ensure comprehensive redevelopment. 

Even when landowners and occupiers are prepared to sell by agreement, site assembly may still be fraught with problems and may prevent comprehensive redevelopment from taking place. The iron works and petrol station site case studies, in particular, demonstrate the importance of protecting reclaimed development sites against the inward migration of contaminants from adjoining sites. Recontamination of the development site in this way may totally negate the work already undertaken, may create 'pathways' for contaminants to reach housing occupiers, services and structures, and is likely to result in the need for even more costly site treatment - hindered by the presence of the newly built homes. 

Identifying potential problems 

In all of the case studies, the developers employed a suitably qualified consultant to undertake a preliminary assessment of the subject site in order to identify any possible hazards that might affect future development. In some cases, this desk study identified the principal site problems but in other cases the full extent of contamination and other difficulties, such as major underground structures, were only revealed by an 'intrusive' investigation (such as drilling bore-holes). 

No ground investigation can guarantee to locate all contaminants that may exist within a site but the case studies demonstrate how developers can gain a good understanding of site conditions. A thorough investigation can assess, with a reasonable degree of certainty, the likelihood of any contamination being present, the nature of the contaminants themselves and the media in which they are located. 

Several case studies, including a former dye works and a shipbuilding works, illustrate the importance of taking a number of samples, solid and liquid, from different parts of the site and at regular depths. The development team can use the preliminary site assessment undertaken by the environmental consultant to plan a cost-effective intrusive site investigation, which may combine both geo-technical and environmental requirements. This site investigation should locate possible contaminants with a reasonable degree of accuracy. In several of the case studies this information was used to design a site-specific remediation strategy that helped reduce the amount of waste material disposed of to landfill sites.

The results of the site investigation will be presented in a detailed report, which should provide a step-by-step account of the processes undertaken. The report should be of a non-technical nature in order that the developer and appropriate regulatory authorities may understand it. Current good practice and suggested best practice imply that, in order to achieve its purpose, the report must include information relating to the site history, sampling strategy, analysis of results, maps showing trial-pit and bore-hole locations, site profiles, remediation strategies and a set of summary conclusions. Most of the case study site reports supplied to the researchers met these criteria but a small number were inconclusive, failing to provide adequate advice to the intending developer. These reports would also have been of little use to future purchasers. 

Preparing contaminated land for development

Various options exist for remediating different types of contamination. These include:

  • Excavation and disposal
  • Containment (in-situ or ex-situ)
  • Soil treatment methods

These broad groups cover many different techniques (the research report describes several briefly, with references to more detailed source material). Selecting the most appropriate options will often have a significant impact on the viability of a housing development. 
The choice of remediation method may be influenced by a number of factors:

  • Cost of the works relative to site value or end value of the proposed development;
  • Neighbouring land uses;
  • The nature of the proposed housing development;
  • Legal and regulatory issues;
  • Surrounding environment, which may rule out some options due to environmental or social constraints;
  • Geography, geology and hydrogeology, which may limit the range of solutions;
  • Time-scale, for example meeting market demands or compliance with planning/regulatory requirements;
  • Technical limitations of the treatment processes, evaluation and agreement as to any residual risks.

For most, if not all, of the developers on the case study sites, cost and speed of completion were the main drivers in the selection of remedial methods. Development of sites in built-up areas may preclude the use of treatment methods that involve large production of dust, noise and/or odours; this was a particularly important consideration on a former petrol station site, for example. All of the case study site developers used 'tried and tested' site remediation methods and, in all of the cases studied for inclusion in the report, there was little evidence of 'innovative' treatment methods even being considered. 

The case studies

The ten case studies included eight where the development had already been completed or was underway at the time of the research, one that had not started and one that had been abandoned by the intending developer. The previous site uses, remediation methods employed, housing types, site sizes and contaminants were:

  • Brickworks, shallow mine workings, road haulage, 'made ground': This site was prepared for private housing development by excavating and disposing of the worst contaminated material to a landfill. The contamination comprised heavy metals and hydrocarbons. On-site encapsulation was used to deal with some unsuitable material but a 'plus factor' in the remediation was the ability to sell ash for the manufacture of building blocks. 
  • Cotton mill, bleach works, oil seals manufacture: The intending developer of this site abandoned the project due to problems with the planning authority, contamination from heavy metals and hydrocarbons, and access problems. The developer wanted to build private houses for rent but the council wanted housing for sale and would not support a grant application.
  • Dye works, chemical works, railway, cattle pens, coal merchants, electric light bulb manufacture, oil depot and scrap-yard: The site was contaminated with heavy metals, hydrocarbons, PCBs. There was also methane in the soil. Remediation comprised on-site sorting, mixing and re-distribution of material. Gas protection measures were installed in a 'managed housing' development.
  • Iron works, lime kiln dock, timber yard, town gas works: Situated close to the city centre, this site had a long history of different uses and formed part of a larger industrial area. The local authority wanted to see a comprehensive remediation programme for the whole area and this has delayed commencement of the project. Contamination included heavy metals, sulphates, ammoniacal nitrogen. The proposed development is for private apartments.
  • Landfill: Treated by sorting, mixing and redistribution of material, this site has been redeveloped as a mixed tenure scheme comprising houses for sale and rent, and a children's home. Gas protection measures were installed, heavy metals contamination was found and dealt with through dilution as part of the process of raising the site level. 
  • Petrol filling station and motor vehicle workshops: In an attractive village location, adjacent to a river and over a major aquifer, the site was extensively contaminated with hydrocarbons. Bio-remediation was used to treat the contamination. Heavy metal contaminants were also found and the local authority asked for these to be removed, even though they did not exceed current guidance for open space.
  • Rail yard forming part of a town gas works: Part of what was once the largest gas works in the world, several developers were involved on this site, providing homes for sale and rent. 'Cover and contain' was the selected remediation method for the original development but different methods have been used for subsequent developments, including the installation of a geo-synthetic membrane in the garden areas. 
  • Road haulage: Arsenic and gas works wastes were found on this site, which was redeveloped to provide bungalows for older people and houses for sale. Excavation and off-site disposal to landfill was the method selected for preparing this site.
  • Shipbuilding works: The local authority had acquired this site on the bank of a river from a major industrial concern and then tackled the problems of remediation and redevelopment. Even though it was contaminated with heavy metals, local people used the site as informal recreation space and were reluctant to see it redeveloped. The council, a private housebuilder and a housing association adopted a partnership approach to create a mixed development of houses for sale and to rent, shared ownership, commercial buildings and public open space. Site preparation consisted of partial off-site disposal, partial on-site disposal and dilution of the contaminants.
  • Timber mill: A small site contaminated with heavy metals, polycyclic aromatic hydrocarbons and sulphates, it also contained some mature trees, which the council wished to see retained. A shared ownership housing association development, the site was prepared by excavation and off-site disposal, together with 'cover and contain'. The trees were retained and reinforced with additional landscaping. 

Conclusions and recommendations

The research identified eleven distinct phases in the redevelopment of previously used land, leading to conclusions and recommendations relating to each phase. The principal findings for each phase were:

Project inception - several case studies confirmed the importance of developers and regulators adopting a flexible approach in order to achieve the redevelopment of 'previously used' or 'brownfield' land and buildings.

Site acquisition and site assembly - one of the studies, a former bleach works, illustrated the fact that whilst landowners may have unrealistic ideas about the value of their land, they may be trapped by historic valuations and by the land being used as collateral against loans. 

Site assessment - The case studies demonstrated that all site assessments benefited from an historical study followed by an on-site investigation. 

'Contaminant-pathway-receptor' - The case studies proved that it may not be necessary to remove all contamination from the site but it may be feasible to break or remove the 'pathway' instead. This implies that in preparing a conceptual model for assessing the site, all possible linkages should be considered. 

Detailed design - once the site has been investigated, developers and planners need to be prepared to consider alternative remediation strategies and different layouts. 

Feasibility study - having completed the site assessment and having identified all potential pollutant linkages, the revised design should be the subject of a comprehensive review by the development team.

Planning and regulatory approvals - the case studies show that close liaison with the regulators during the earlier phases will help ensure that the necessary information has been collected and can be presented in support of the applications. 

Development finance - banks and other financial institutions are more prepared to provide development finance for 'previously used' sites than they were a few years ago. 

Tendering - the appointment of contractors with experience of site remediation can be beneficial, as they may be able to suggest ways of undertaking the work. 

Construction - all of the case studies (where work had been completed) confirmed the importance of ensuring that the site remediation/preparation works are properly supervised and fully recorded - including photographic and written records. 

Sales and marketing - developers differed in their approach to what information was provided to prospective purchasers and tenants. Some, as in the landfill site, produced a fairly comprehensive statement of site history and site preparation works, making this available to purchasers and tenants. There was no evidence that this deterred potential residents and the development was over-subscribed. Others preferred to rely on providing information as part of the package of documents sent to purchasers' solicitors. On the whole, the developers recognised the importance of being open with information relating to the site and its development, as they felt any attempt at concealment was likely to have an adverse effect once it was discovered.

About the study

The study examined ten case studies geographically distributed throughout England to illustrate the redevelopment process and highlight some of the problems faced by developers when tackling 'previously developed' land. The sites were previously used for differing purposes and various methods were employed for site remediation. The new developments included social housing, shared ownership tenure, apartments and executive homes. The researchers reviewed the site investigation techniques and reports, discussed the development with the developers, town planners, environmental consultants, architects and engineers. The procedures employed in developing the sites were reviewed against current good practice, guidance and legislation, before being distilled into a brief description of how the redevelopment of each was tackled.

The lessons learned from the case studies were set into a framework of eleven phases of redevelopment. For all of the case studies, the researchers used a 'contaminant-pathway-receptor' risk model, where the contaminant (or source) relates to a substance or group of substances with the potential to cause harm. The receptor (sometimes referred to as the target) is someone or something, such as buildings, crops or animals, that could be harmed by the contaminant and the pathway is the route, for example the air, soil or water, through which it could reach the receptor. 

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