Annex A: Guidance on the assessment of land affected by contaminants

A.1A substantial amount of guidance on the assessment of contaminated land has been published to support the implementation of Part IIA of the Environmental Protection Act 1991. Most of this guidance is contained in the joint Defra/Environment Agency Contaminated Land Research Reports (CLRs). This guidance can be used to support the assessment process set out in Section 2. A summary of the reports is set out below and an outline of the process is given in Figure A1147.

A.2For health, risk estimation can be carried out using generic assessment criteria such as contaminant soil guideline values (SGVs) or relevant and appropriate environmental standards. SGVs represent contaminant concentrations which may pose unacceptable risks to health. The development of SGVs for a range of priority contaminants is described in the Defra/ Environment Agency reports CLR 7148, CLR 8149, CLR 9150 and CLR 10151.

A.3CLR 10 describes the Contaminated Land Exposure Assessment Model (CLEA) for deriving SGVs for three different site uses: (i) residential, (ii) residential with plant uptake and (iii) commercial/industrial. In this way the relative importance of each of the pollutant linkages is considered. For example, for residential site use it is assumed residents have private gardens and/ or access to community open space close to the home and that some may use their gardens to grow vegetables. CLR 10 gives details of the conceptual model underpinning each of the standard land uses.

A.4A series of Defra/Environment Agency SGV reports152 contain SGVs for a range of contaminants, one report for each contaminant, and the corresponding TOX reports153 contain the toxicological data used to derive the SGVs. SGVs should be used only in conjunction with the CLR 7 to 10 reports and associated SGV and TOX reports.

A.5The use of ICRCL (Interdepartmental Committee on the Redevelopment of Contaminated Land) document Guidance Note 59/83: Guidance on the assessment and redevelopment of contaminated land154 is no longer appropriate in health risk assessment and has been withdrawn155 by Defra.

A.6CLR 7 provides advice regarding such issues. In certain cases the most appropriate action may be to redesign the building layout. Further guidance can be obtained from the Environment Agency/NHBC R & D Publication 66156.

A.7An alternative to the generic approach is to undertake a more site-specific quantitative risk assessment using the principles of risk assessment or a risk assessment model. Specialist advice should be sought.

  • 1 Distribution of shrinkable clays and principal sulphate:sulphide bearing strata in England and Wales 1 Distribution of shrinkable clays and principal sulphate:sulphide bearing strata in England and Wales
  • 2 Example of a conceptual model for a site showing source–pathway– receptor 2 Example of a conceptual model for a site showing source–pathway– receptor
  • 3 Subsoil drain cut during excavation 3 Subsoil drain cut during excavation
  • 4 Ground supported floor - construction- see par 4.7 4 Ground supported floor - construction- see par 4.7
  • 5 Suspended timber floor - construction - see par 4.14 a (i) Diagram 5 Suspended timber floor - construction - see par 4.14 a (i)
  • 6 Suspended floor - preventing water collection-see par4.14a Diagram 6 Suspended floor - preventing water collection-see par4.14a
  • 7 Typical floors exposed from below Diagram 7 Typical floors exposed from below
  • 8 Damp proof courses- see par 5.5-b Diagram 8 Damp proof courses- see par 5.5 (b)
  • 9 Protecting inner leaf - see par 5.5c Diagram 9 Protecting inner leaf - see par 5.5c
  • 10 Protection of wall head from precipitation - see par 5.9(c) Diagram 10 Protection of wall head from precipitation - see par 5.9(c)
  • 11 Insulated external walls examples -see paragraphs 5.10, 5.13 and 5.17 Diagram 11 Insulated external walls examples -see paragraphs 5.10, 5.13 and 5.17
  • 12 UK zones for exposure to driving rain 12 UK zones for exposure to driving rain
  • 13 Window reveals for use in areas of severe or very severe exposure to driving rain - see paragraph 5.32 Diagram 13 Window reveals for use in areas of severe or very severe exposure to driving rain - see paragraph 5.32
  • 14 Accessible threshold for use in exposed areas- see par 5.33 Diagram 14 Accessible threshold for use in exposed areas- see par 5.33
  • Table 1 Volume change potential for some common clays Table 1 Volume change potential for some common clays
  • Table 2 Examples of sites likely to contain contaminants Table 2 Examples of sites likely to contain contaminants
  • Table 3 Examples of possible contaminants Table 3 Examples of possible contaminants
  • Table 4 Maximum recommended exposure zones for insulated masonry walls Table 4 Maximum recommended exposure zones for insulated masonry walls