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Soil contamination - Issues and practical considerations

The previous land-use of a site should be considered before greenspace establishment. Pollution levels may be such that vegetation establishment is not feasible on the site without some form of remediation. This may be because of direct toxicity to the vegetation through root uptake of pollutants, toxicity to the soil communities that are responsible for supplying nutrients via the breakdown of organic matter or due to impacts of pollution to other receptors (for example site users, or ground and surface water).

Background

The creation of greenspace on polluted land is increasingly being seen as a low-cost solution to dealing with the past legacy of industrial activity in the UK. There are an estimated 20,000 hectares of contaminated land in the UK, much of which is currently left derelict or underused. This is particularly true in regions that have a long history of industrial activity and have suffered a decline in inward investment in recent decades, resulting in large areas of potentially contaminated land where land value is too low to make remediation cost-effective.

Establishing vegetation on polluted sites can improve the aesthetic appearance of the area, with resulting economic benefits. Many sites may have an impact on local air and water quality, or on adjacent sites – this may be through erosion, surface run-off, or leaching of pollutants through the soil profile. The roots of vegetation can stabilise soil, reducing surface water run-off and the erosion of potentially contaminated materials into surface water or adjacent areas. Many polluted sites are not capable of supporting vegetation without the incorporation of soil amendments. As well as improving soil structure and providing plant nutrients, amendments may also immobilise pollutants and aid with the degradation of organic contaminants.

Practical considerations

Part IIA of the Environmental Protection Act (1990) is the legislative framework for identifying and dealing with contaminated land in the UK. This defines contaminated land as that which is causing or likely to cause a significant risk of significant harm to a number of specified receptors, including human health, controlled waters, property, livestock and crops, and ecological systems. Ecological systems are considered to be receptors only if they are covered by statutory protection (for example, Sites of Special Scientific Interest and Ramsar sites). This means that former industrial sites with elevated (above-background) levels of pollution within their soils may not be defined as contaminated if they do not possess a source–pathway–receptor linkage, for example if the pollution levels are high, but there are no receptors or the pollution is immobile so there is no pathway to the receptor.

The effect of establishment of greenspace should also be assessed prior to site development. The site may not be deemed to be contaminated under Part IIA in its current state, but the establishment of greenspace may create pathways to receptors that did not exist previously. The creation of habitats may encourage protected species to the site that were not present before, and if a pathway then exists to these species, the land may then be designated as contaminated. Similarly, if the site is now attractive, people may begin to visit it, potentially creating a pathway to human health.

There is a substantial amount of guidance available from the Environment Agency covering proposed development on land that may be contaminated. Normally development will involve commissioning an Environmental Consultant to carry out a site investigation of past land uses to determine whether the site is likely to be contaminated, if necessary followed by an intrusive site investigation.

Once a clear picture of the site conditions has been established, development of the site will need to be planned. This may include a remediation strategy, the design of the greenspace to manage any risk that may be present on the site, and the species of vegetation that are selected.

Case studies

Newlands

Launched by the Deputy Prime Minister in July 2003, this £59 million project aims to reclaim large areas of derelict, underused and neglected land across north-west England, transforming them into thriving community woodlands and significantly increasing woodland cover in the region.

  • Phase 1 – reclaiming 435 hectares of derelict, brownfield land. The first 5-year phase is reclaiming land throughout the Mersey Belt area for community woodland uses and economic growth. Areas targeted include Greater Manchester, Cheshire and Merseyside.
  • Phase 2 is under development, and will encompass Cumbria and Lancashire.

All Newlands sites were selected from a database of derelict, underused or neglected land, produced by an analysis of aerial photographs, the National Land Use Database and Unitary Development Plans.

This initial study identified 3800 sites of more than 1 ha, of which 1600 were previously developed brownfield sites deemed potentially suitable for woodland planting under the Newlands scheme.

These sites were prioritised according to the results of a Public Benefits Recording System assessment. This methodology was designed to measure the public benefit that could be delivered through the regeneration of each site, and includes assessments of social, economic, environmental and accessibility benefits.

Newlands received a significant amount of funding from the Northwest Regional Development Agency, and is being delivered in partnership with the Forestry Commission, as well as a number of delivery partners including:

  • Red Rose Forest
  • The Mersey Forest
  • Pennine Edge Forest
  • Groundwork
  • Forest Enterprise
  • Mersey Basin Campaign
  • British Trust for Conservation Volunteers.

Various local authorities in the area are also involved, along with several major landowners including United Utilities and Greater Manchester Waste Disposal Authority.

Services

Forest Research, in collaboration with Arup, has developed and refined a biological indicator methodology for assessing the feasibility and risk–benefit of direct vegetation establishment on contaminated land.

The methodology has the following aims:

  • To determine the viability of phytoremediation technologies for removing or stabilising contaminants
  • To act as an indicator of the risk of contaminants becoming available to primary consumers through ingestion of plant material containing elevated concentrations of metals.
  • To provide working examples showing the efficacy of the indicator methodology for reducing waste production and remedial costs of redevelopment works, while improving the quality of the final landscape.

Forest Research has considerable experience in conducting both nursery- and field-scale experiments on contaminated land. This includes the evaluation of risk to ecological receptors, species selection and the use of soil amendments to improve soil quality, immobilise contaminants and improve microbial degradation of organic contaminants.

Forest Research also offers consultancy services in the site investigation of contaminated sites for a green end-use, and advice and guidance on the required standards for soils to establish vegetation, the use of soil amendments, and the most suitable species for specific site conditions.

Forest Research is able to conduct standard and bespoke ecotoxicological testing for the risk assessment of contaminated land regarding ecological receptors. These include plant growth and contaminant-uptake tests, soil invertebrate and microbial tests, and soil characterisation.

Further information

Forest Research Best Practice Guidance

Hutchings, T., Sinnett, D. and Doick, K. (2006). Soil Sampling Derelict, Underused and Neglected Land prior to Greenspace Establishment (PDF-956K). Best Practice Guidance for Land Regeneration, BPG Note 1. Forest Research, Farnham.

van Herwijnen, R. and Hutchings, T. (2006). Laboratory Analysis and Soils and Spoils (PDF-294K). Best Practice Guidance for Land Regeneration, BPG Note 2. Forest Research, Farnham.

Other resources

Doick, K. and Hutchings, T. (2007). Greenspace Establishment on Brownfield Land: the site selection and investigation process (PDF-1060K). Forestry Commission Information Note 91, Edinburgh.

Hutchings, T.R. (2002). The Opportunities for Woodland on Contaminated Land (PDF-1018K). Forestry Commission Information Note 44, Edinburgh.