The role of quantitative risk assessment tools to support the assessment of environmental risk during the planning process illustrated using case study data

Brière de l’Isle, B., Pitchers, R., Turrell, J., WRc plc



The UK planning process for a waste treatment plant requires a robust assessment of the environmental risks that may be associated with the proposed activity.  This paper details how quantitative risk assessment (QRA) tools can be used to provide evidence to make an informed decision on risks and identify appropriate management options.

The first part of this paper identifies the three main steps within a QRA. The first requires development of a conceptual model of the proposed activity which incorporates site specific information. This can be used to determine the nature of the contamination and to examine the potential pathways for spreading contamination from the transport and processing of waste materials to identified receptors. Pathways commonly include: the potential for loss of material through release of dust and pathogens during transport and the generation of bioaerosols and odours during treatment. Receptors might include assessment of risks to controlled waters, human, animals and plant health and the wider environment.

The second step in the process is to use probability modelling to quantify the outcomes of a chosen activity taking into account a range of ‘what if’ scenarios, e.g. weather conditions, to generate probability curves and define the levels of uncertainty of selected assumptions. These risks can be determined for specific operating periods.

The third step is to make an assessment of the overall risk in the context of existing procedures and to evaluate whether the risks are deemed to be acceptable. This requires communication of risks in a meaningful way to improve the understanding of involved and interested parties.

A worked example is provided in Part 2 of this paper of a UK case study using this approach which focussed on an assessment of odour and bioaerosols from a proposed waste treatment plants for use in very sensitive area.

Keywords: Quantitative risk assessment, Waste treatment plant, Bioaerosols


There is a legal obligation for the waste management industry and its developers to submit a planning application to the Local Authority for proposed development of treatment facilities or where significant modifications are wanted at existing works. For sites over 0.5 hectares, an Environmental Impact assessment is required and an Environmental Statement should respond to the potential of significant adverse effects on the environment. The screening opinion highlights hazards that are largely qualitative and do not satisfy public concerns.

For example, a Quantitative Microbial Risk Assessment (QMRA) could provide evidence of protection against pathogens. A formalised QRA tool, when used correctly, can significantly improve the outcome of a planning application as it provides a better understanding of the problem. Figure 1 provides a simplified decision tree to identify when a detailed QRA may be required. Part 1 of this paper provides further information on the three key steps required for a QRA:

Step 1 – Problem formulation and development a site specific conceptual model

Step 2 – Use probabilistic risk assessment tools to quantify the risks; and

Step 3 – Evaluate the consequences i.e. determine whether the identified risks are acceptable for the proposed activity.

A case study is provided in Part 2 to illustrate how this approach might be applied to support a planning application for a new waste treatment plant.  The social aspects which include perception and communication of risk, and risk screening and monitoring are not discussed in detail but represent a significant part of the overall risk management procedure.

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