Risk Assessment: Sources, Pathways and Receptors

Background

Risk Assessment forms the core of the contaminated land investigation and assessment process. The purpose of investigations is to obtain information on sources, pathways and receptors present on or adjacent to a site. The presence of a linkage between these may then constitute a risk, the significance of which must be assessed and is dependent upon a number of factors.

Essentially, the process seeks to determine what risk, if any, is created by the presence of contaminants through determining if there are pathways through which the contaminants may impact sensitive receptors, and is the risk acceptable or not.

This need to make judgments about the degree of risk is crucial in determining what action to take. In many cases it is often neither feasible nor realistic to think in terms of total clean up of past damage. The overall approach in dealing with past land contamination is therefore one of risk assessment and management, identifying, assessing and judging risks, taking actions to mitigate them, as well as monitoring and reviewing progress.

What Do We Mean By Risk?

Risk is a combination of the probability, or frequency, of occurrence of a defined hazard and the magnitude of the consequences of the occurrence.

The idea of the “pollutant linkage”

In the context of land contamination, there are three essential elements to any risk:

• Source (contaminant) – a substance which is located in, on or under the land and has the potential to cause harm to human health, water resources or the wider environment;

• Pathway – the means or route by which a source of contamination can migrate; an identified receptor can be exposed to, or be affected by an identified source;

• Receptor – something which could come to harm, including human health, water resources, surface water courses or the wider environment. 

Each of these elements can exist independently. They create a potential risk where they are linked together. The linked combination of “contaminant – pathway - receptor” is known as a pollutant linkage.

On any individual site, one single pollutant linkage or number of different pollutant linkages may be present. Different pollutant linkages may also be related. The same receptor may be linked to a number of different contaminants via the same migration pathway. Contaminants can migrate to a receptor via more than one pathway and receptors maybe at risk from more than one source of contamination.

Phase 1 and  Phase 2 site investigations are used to identify potential sources, pathways and receptors. Each pollutant linkage needs to be separately identified, understood and dealt with if appropriate.

Without a pollutant linkage, there is not a risk – even if a contaminant is present. Where there is a pollutant linkage, and therefore some measure of risk, it is important to identify whether that risk is significant. The level of risk needs to justify the actions taken to deal with the risk.

The question of whether risk is unacceptable in any particular case requires scientific and technical assessment of the circumstances on the site and the use of appropriate criteria to judge the risk combined with professional judgment.

In some cases it is possible to use contaminant fate and transport modeling through complex risk assessment models to determine the level of risk present.

Most commonly the Contaminated Land Exposure Assessment (CLEA) model is used to make a preliminary generic assessment of the significance to human health of contaminants found; other models such as SNIFFER, RBCA, the Environment Agency R&D 20 models maybe used to make assessments, dependent upon the nature of the sources, pathways and receptors identified.

The nature and level of risk is defined by variability in the condition and circumstances of any particular piece of land. The details of the use of the land itself, as well as the surrounding land, determine whether particular receptors and pathways are present and, if they are, the extent to which they might potentially be affected by contamination. The same concentration of a contaminant can have widely differing implications in different circumstances. Risk assessment allows this to be considered in a structured and pro-active way so that appropriate and cost effective decisions are taken.

Capabilities

ESG has been involved in a wide range of development projects using risk assessment as a key tool within site investigations of potentially contaminated sites. We are able to provide a comprehensive contaminated land investigation service including:

• Production of Phase 1 Desk Study reports through extensive information gathering, analysis and interpretation;
• Designing, commissioning and supervising Phase 2 Intrusive Site Investigations, to meet the requirements of both the client and statutory authorities;
• Design & Implementation of remedial schemes and undertaking post remediation monitoring (Phase 3);
• Validation of remediation (Phase 4) and production of Post Remediation Validation Reports and remediation statements;
• Liaison with statutory authorities (e.g. the Environment Agency, local authorities, HSE etc.);

ESG undertake site investigations and reporting in accordance with relevant guidelines, including BS 10175: 2001 and Environment Agency guidance.

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