Briefing Note

Investigating Sites for Contamination - An overview

Contamination is a material consideration in any development

Legislation

Stage 1: Desk Top Assessment

Review of historical maps etc. including a site walkover, to identify:Brownfield Site

  • Sources - Likely contaminants and distribution on the site, together withsignificant off site sources, e.g. landfill sites within 250m.
  • Receptors – Typically end users, groundwater and protected ecosites.
  • Pathways – Linking the Sources and Receptors. 
  • The relationship between Sources, Pathways and Receptors is called the Conceptual Site Model (CSM). The CSM is the basis of subsequent investigation, riskassessment and remediation.

Window Sampler RigStage 2: Site Investigation

Intrusive borehole and/or trial pit investigation with laboratory analysis of samples:

  • The intrusive investigation proves or refines the CSM.
  • Multi-stage investigation may be required to provide enough detail andcertainty.
  • Contamination investigation is usually combined with geotechnical investigation.
  • Contamination investigation is not always necessary if the Desk Top Assessment indicates that the site is unlikely to be contaminated. 
  • However, site investigations frequently reveal unexpected pockets/areas of made ground that may be contaminated and may require sampling and analysis.

Stage 3: Interpretive Report

Factual report together with a risk assessment and outline recommendations for remediation and/or further work (if required).

  • The Environment Agency has produced a methodology and tools for assessing the risk from contamination in the ground, collectively called ContaWindow Sampler Rigminated Land Exposure Assessment (CLEA).
  • The Environment Agency has published conservative Soil GuidelineValues (SGVs) for some contaminants.  CLEA can also be used to derive less conservative Site Specific Assessment Criteria (SSACs), and Generic Assessment Criteria (GACs) for contaminants where there is no SGV.
  • If the concentration of a contaminant in the soil exceeds the assessment criterion, remediation may be necessary.
  • A good CSM combined with sophisticated use of CLEA can reduce or eliminate the need for remediation, which can help to reduce development costs and deliver faster construction programmes.

 

Seminars: SMP is pleased to offer free seminars on Contaminated Land, Site Investigation Work and other areas.  Please contact us on Engineers.smp@mistral.co.uk

 

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