Last edited 13 Dec 2018

Solid and liquid contaminants site risk assessments

Contaminated land is land that presents a hazard in the form of material that has the potential for harm. Assessment of the risk of harm is based on the likelihood, frequency and seriousness of the adverse consequences of contaminants. See contaminated land for more information.

Where development sites are affected by solid or liquid contaminants, Approved document C, Site preparation and resistance to contaminants and moisture, suggests that the principles of risk assessment should follow the ‘source–pathway–receptor’ relationship, or 'pollutant linkage', where:

The approved document suggests that this can be achieved by:

  • Treating the contaminant. The use of physical, chemical or biological processes to eliminate or reduce the contaminant’s toxicity or harmful properties.
  • Blocking or removing the pathway. Isolating the contaminant beneath protective layers or installing barriers to prevent migration.
  • Protecting or removing the receptor. Changing the form or layout of the development, using appropriately designed building materials.
  • Removing the contaminant.

The assessment of risk should adopt a tiered approach. A preliminary risk assessment should be undertaken, and depending on the outcome, either a generic quantitative risk assessment (GQRA) or detailed quantitative risk assessment (DQRA), or both, may be necessary.

CLR 11 Model Procedures for the Management of Land Contamination, Defra/Environment Agency, 2004 suggests that the stages of risk assessment should be:

If unacceptable risks to a receptor are identified, remedial measures must be used to break the pollutant linkages.

Depending on the contaminant, three types of remedial measures can be considered:

  • Treatment.
  • Containment.
  • Removal.

Treatment may include biological, chemical and physical techniques carried out on or off site to decrease the mass, concentration, mobility, flux or toxicity of contaminants.

Containment generally involves encapsulation of material containing contaminants or the use of cover systems, placing one or more layers of materials over the site to: break the pollutant linkage, sustain vegetation, improve geotechnical properties, and reduce exposure to an acceptable level. Vertical barriers may also be required to control lateral migration of contaminants. Maintenance and monitoring may be necessary to ensure integrity from burrowing animals, gardening, excavations by householders and so on.

The containment or treatment of waste may require a waste management licence from the Environment Agency.

Removal involves the excavation and disposal to of contaminants to licensed landfill sites.

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