The Part IIA statutory guidance states that there are two steps in applying the definition of contaminated land:
• Identification of potential source-pathway-receptor combinations – pollutant linkages;
• Assessing risk to receptors from these pollutant linkages.
Further guidance on this process is provided in the Defra and EA CLR11 Model Procedures document which provides the framework for conducting contaminated-land risk assessment in the UK. Demonstration that the framework has been followed will help to satisfy a local authority that the conclusions of the risk assessment are valid.
The CLR11 document recommends a tiered approach to risk assessment:
Tier 1: Preliminary Risk Assessment;
Tier 2: Generic Quantitative Risk Assessment (GQRA);
Tier 3: Detailed Quantitative Risk Assessment (DQRA).
The tiered approach streamlines the risk-assessment process, focusing effort on areas where risks are potentially unacceptable. This is essentially an iterative process where the earlier the exit from the process, the higher the likely remedial costs.