The importance of risk based conceptual site models

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Courtesy of NANO IRON s.r.o.

This article highlights the importance of Conceptual Site Models (CSMs) to NanoRem. CSMs summarise the source-pathway-receptor linkages (SPRL) and significant uncertainties at a site in easily understood diagrams. They are updated as more information becomes available. Used in the relevant legal context, they inform risk assessment and risk management decision making.

The NanoRem pilot sites need CSMs to ensure shared understanding site conditions and to design an appropriate remediation strategy. To assist them, in July 2014 LQM delivered an online seminar on creating a CSM.

CSMs provide a simplified vision of the site

The CSM highlights the relevant features of the site and adjacent area. It comprises plans and cross section(s)) together with a matrix or network diagram to identify source-pathway-receptor linkages (SPRL) accompanied by summary text (Table 1).

CSMs aid understanding and communication among stakeholders.

Creating the CSM deepens its creator’s understanding of the site thereby improving risk assessment and remediation outcomes.

The CSM is a communication tool that focuses attention on the key risk driving features of the site. This allows all stakeholders to rapidly understand the nature of problem. It also facilitates dialogue, allowing stakeholder questions to be addressed, which in turn further improves the understanding of the site.

CSMs highlight the relevant legal context

Legal drivers affect what actions may be required to manage the presence of contaminants at a site or dictate the nature or location of relevant receptors. The CSM is developed in the light of these drivers and the legal context is clearly stated within the CSM.

Plans and cross sections usefully summarise the site conditions while relevant source pathway receptor linkages (SPRLs) can be depicted on a network diagram (Figure 1). Candidate remediation strategies can then be tested against the CSM to see whether they break the SPRLs.

CSMs identify uncertainties and drive the risk assessment

As the CSM is created, unknowns become apparent. The CSM captures such uncertainties and assumptions, so the level of understanding of the problem is apparent. Examples of uncertainties and assumptions are in Box 1.

Uncertainties identified during one phase of investigation can comprise the objectives of subsequent phases; thereby refining the risk assessment.

CSMs explain the problem at hand.
Several CSMs may be created to consider different aspects of the project. For NanoRem there will be CSMs for:

  • “the problem” driving the need for remediation e.g. contaminant reaching river;
  • The “remediation solution” e.g. nanoparticles destroying the contaminant;
  • The predeployment risk assessment (PDRA) for renegade nanoparticles.

The latter considers the NPs as the “Source” in order to consider possible risks of injecting nano particles into groundwater.

Figure 2 shows a plan view for the remediation solution showing where injection wells are to be located; Figure 3 isthe associated network diagram showing how the linkage would be broken by removing the source.

Concluding thoughts: CSMs in NanoRem
NanoRem will produce CSMs for each pilot site showing the problem to be solved and demonstrating the extent to which nanoremediation has solved the problem. A separate CSM will be produced to consider possible risks of injecting NPs into groundwater. CSMs will form part of the evidence NanoRem will require to provide field evidence of the safe and effective deployment of nanoparticles (NPs) to remediate polluted groundwater.

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