Guidelines for Environmental Risk Assessment and Management
[This document refers, in a number of instances, to the then Department of the Environment, Transport and the Regions (DETR). The text of this document has not been updated since the transfer of environmental protection functions to Defra.]
Chapter 4
Problem formulation
4.1 Introduction
Clearly setting out the problem at hand and the boundaries within which any decisions are to be applied is important in risk assessment. Risk assessments are generally employed where the outcome of a given activity is uncertain. It is often tempting to omit any formal documented definition of the problem, particularly where there is pressure to complete the risk assessment quickly. However, failure to define the problem clearly is to lose the focus of the assessment itself, and may even result in an inappropriate output.
Stakeholders have an important role to play in problem formulation and their early involvement will tend to make risk management decisions more effective and durable (Section 3.8).
Describing the problem in clear and unambiguous terms will assist in selecting the level and type of assessment methodology used, and improve the risk management decision. It will also provide an important baseline should the process or eventual decision be challenged or audited. A range of issues pertinent to problem formulation which should be considered before undertaking any risk assessment is set out below.
4.2 Defining the intention
An important prerequisite to formulating the problem is a complete definition of the intention (Section 1.7). the intention will often be to carry out an activity which may add to existing risks. Sometimes the intention may be to act in order to reduce risks. this in itself does not alter either the need for, or the nature of, the risk assessment.
For risk assessors intimately concerned with a particular intention, it is easy to make implicit assumptions when defining the intention or take account of knowledge that will not be known to anyone who uses the risk assessment later. Consequently, recording the definition of the intention from the outset provides significant benefits by making clear to anyone using the assessment exactly what was taken into account. A good statement of the intention will also facilitate monitoring and feedback and help to determine whether discrepancies between forecasts and outcomes were caused by poor judgement, lack of knowledge or other factors.
To assist in defining the intention, it is helpful to consider the following four facets.
- What was the situation before the intention - the baseline?
- What are the characteristics of each contributing element of the intention - the components?
- How are the components related and what steps or processes are involved in the intention - the process?
- What will be the situation after the intention - the forecast?
Baseline
the baseline refers to the state of the environment both in the locale of the hazards arising from the intention, and over the area where harm may be expected. Whereas the temporal and spatial boundaries of a hazard may be easily defined, the effects can be far more wide-ranging; the risk assessment should reflect this. the baseline will also include a record of all other relevant pre-existing hazards that may affect the outcome of the risk assessment. For example, if the intention is a new water abstraction from a river, there might be a risk of low water flows affecting aquatic plants. Existing abstraction levels would therefore be an important piece of baseline information.
Components
A unifying principle to bear in mind during problem formulation and throughout risk assessment is the connection between the source (of the hazard), the pathway, the receptor, and the impact. It is important that connectivity, or potential connectivity between these four components can be shown. If any of these components is missing then the risk assessment need go no further. Each of the risk components will have characteristics that may affect the consequences of an intention. For example, the chemical composition and combustion products of diesel fuel differ from unleaded petrol. To assess the risks associated with a road building programme, it will be necessary to estimate the relative numbers of diesel and petrol vehicles, and, thereby, their relative effects on air quality. A traffic flow dominated by diesel vehicles will have different effects from a flow dominated by petrol vehicles.
Process
Each component of the intention can relate to other components as part of an overall process. For instance, the risk that a pollutant will reach an aquifer depends on the relationship between such things as groundwater flow, rainfall and geological conditions. In bringing together each of the components, further factors will be brought in to play which may affect the risk. For example, in establishing a new chemical plant there are important factors to consider before, during and after the project. Some of these factors include:
- before - clearing the site before construction starts;
- during - water and energy consumption, processes, emissions, wastes and materials transported to and from the site in both the construction and operational phases; and
- after - the final decommissioning and demolition of the site.
the forecast reflects the need to be able to define what may happen as a consequence of the intention. this is clearly very difficult, but some of the most important consequences may be determined here. For instance, the situation after a flood may be very similar to the situation before the flood. After decommissioning a nuclear power station, however, the adjacent land and the waste disposal site taking the redundant materials may be contaminated with radioactive material for a long time.
4.3 Justifying an intention
Chapter 3 provided a broad overview of the social aspects of risk, stressing that such issues should be considered at all stages of the risk assessment process. Having defined the overall intention and the problem facing the decision-maker, it should then be possible to address the benefits to society from the intention, for comparison with the risks which society is being asked to accept, in order to judge whether society is prepared to tolerate the risk or not.
the assessment of both proposed and existing risks includes economic factors (costs and benefits). Increasingly, socio-economic analysis is used for this purpose.
4.4 Setting the boundaries
An important requirement for any risk assessment is ensuring that its boundaries are clearly and logically selected. the boundaries can relate to factors such as:
- the spatial extent and time-scales over which the intention and any consequences may be considered;
- when the output from the risk assessment is required;
- the resources that can be assigned to the risk assessment;
- the purpose for which the output from the assessment is required; and
- the weight of decision to which the risk assessment will contribute.
It is important to document the grounds for selecting these boundaries.
It is rare for hazardous events to occur without one or more factors controlling their timing, intensity and duration. While this may appear self-evident, it is important for the selection of risk reduction options. If controlling factors are not considered in the problem formulation stage, difficulties may arise when choosing the most appropriate risk reduction options. In relation to flooding, for example, factors such as the prevailing meteorological conditions, state of any flood defences, soil moisture deficit, and hydraulic capacity of the flood channel will all control the hazard to some extent. Equally, plant operator performance, levels of investment, training and even staff morale can be important factors in controlling risks from a chemical plant.
Some of the factors that control policy may initially be difficult to identify, but they are as important in their link to the hazard itself as are the more specific risks mentioned above. the policy options to reduce the environmental impact of power generation may be influenced by the degree of society's reliance upon electricity and, therefore, future population growth may well be one of the controlling factors.
In carrying out a policy-level or project-level risk assessment (Section 1.3), the factors controlling the hazards need to be clearly defined in the problem formulation stage. Modifying these factors will often be a key consideration in the options appraisal stage (Chapter 8).
4.6 Developing a conceptual model
Conceptual models are useful tools in problem formulation. they present in both visual and written form the hypothesised relationships between sources, pathways and receptors. For example, Table 4.1 and Figure 4.1 present hypotheses of the source-pathway-receptor relationship for petroleum retail sites where historic or ongoing contamination is an issue.
| Table 4.1 Simplified, illustrative conceptual model for exposure to hydrocarbon fuels at petroleum retail sites | ||||||
|---|---|---|---|---|---|---|
| Primary source | Secondary source | Hazard | Transport mechanism | Pathway | Medium of exposure | Receptor |
| Fuel tank | None | Dizziness, CNS depression, potential carcinogenicity | Vapour transport through air | Inhalation of vapours | Air | Humans (forecourt users) |
| Fuel tank | None | Vegetative die back, damage to leaf function | Vapour transport through unsaturated zone | Absorption of vapours | Air | Adjacent vegetation (trees) |
| Fuel tank | None | Derogation of groundwater quality | Product loss and vertical migration to water-table | Dissolution in groundwater | Water | Groundwater aquifer |
| Fuel tank | None | Derogation of surface water | Product loss and dissolution in groundwater | Base flow and discharge to adjacent surface water body | Water | Adjacent river |
| Fuel tank | Contaminated soils | Dizziness, CNS depression | Vapour transport through unsaturated zone | Inhalation of vapours | Air | Humans (recreational users) |
| Fuel tank | Contaminated soils | Skin irritation, contact dermatitis in extreme | Direct contact with contaminated soil | Dermal contact at surface | Soil | Humans (recreational users) |
| Fuel tank | Contaminated soils | Flammability | Vapour transport through unsaturated zone | Vapour build-up in basement void | Air | Humans (residential) |
| Fuel tank | Contaminated soils | Flammability | Vapour transport through unsaturated zone | Vapour build-up in basement void | Air | Property |
| Fuel tank | Contaminated soils | CNS depression, asphyxiation | Vapour transport through | Vapour build-up in | Air | Humans (residential) |
| Fuel tank | Contaminated soils | Derogation of surface water quality | Bulk fluid transport through unsaturated zone | Free product flow to adjacent river | Water | Adjacent river |
| Fuel tank | Free product on water-table | Derogation of soil quality | Evaporation to overlying soils | Vapour phase | Soil vapour | Soil |
| Fuel dispenser | None | Derogation of soil quality | Spillage and percolation through cracked hardstanding | Leaching | Soil | Soil |
| Fuel dispenser | None | Various, potential carcinogenicity | Vapour transport through air | Inhalation | Air | Humans (forecourt users) |
| Spills from customer activity | None | Vegetative die back | Vapour transport through unsaturated zone | Absorption of vapours | Soil gases | Adjacent vegetation (home grown produce) |
| Spills from customer activity | None | Various, potential carcinogenicity | Vapour transport through unsaturated zone | Consumption of contaminated produce | Vegetable produce | Humans (residential consumers of home grown produce) |
| Spills from customer activity | None | Various, potential carcinogenicity | Vapour transport through air | Inhalation | Air | Humans (forecourt users) |
| Spills from customer activity | Contaminated soils | Dizziness, CNS depression | Vapour transport through unsaturated zone | Inhalation of vapours | Air | Humans (forecourt users) |
CNS, central nervous system
Figure 4.1 Simplified, illustrative conceptual model for exposure
to hydrocarbon fuels at petroleum retail sites 
To ensure risk assessments focus on the most important hazards, conceptual models should be flexible and integrate all available information and expert opinion on a given set of hazards.
the level of detail required in the conceptual model will differ depending on the complexity of the risk assessment. A conceptual model can be highly specific and concentrate on just one facet of a large project, or it may be possible to embody the entire intention in one model. For a single chemical affecting a single receptor the conceptual model will probably be simple; in the case of multiple sources and multiple receptors the model will be more complex.
Uncertainty in conceptual models
Uncertainty in developing conceptual models arises from a lack of knowledge, failure to identify hazards, failure to consider the boundaries of the risk assessment correctly, or failure to consider direct or indirect effects. these factors become increasingly important when dealing with multiple stressors in complex situations. It may be appropriate to work with two or more conceptual models where there are alternative hypotheses.
Uncertainty cannot be completely eliminated but should be acknowledged wherever it arises.
Iteration and refinement
It is important to revisit, and where necessary revise, the conceptual model to ensure the underlying rationale is correct. the breadth of the conceptual model is likely to narrow during the risk assessment process. Initial models are often wide-ranging but as further information is accrued certain hypotheses may be discarded. the result is a risk assessment focusing on only the most significant hazards.
4.7 Further information
Key references
Baird DJ, Maltby L, Greig-Smith PW & Douben PET (1996) ECOtoxicology:
Ecological Dimensions, London, UK, Chapman & Hall
An interesting collection of papers addressing the importance of ecological
issues within ecotoxicology, with a particularly relevant contribution
on the evaluation of the importance of indirect effects.
Calow P, ed (1993/1994) Handbook of Ecotoxicology, Vols. 1
and 2, London, UK, Blackwell Scientific Publications
A comprehensive and accessible collection of information on toxicity
tests, how they are carried out, problems associated with them and their
interpretation. Volume 1 concentrates on tests used for prediction while
Volume 2 complements Volume 1 by covering how to deal with test results.
Calow P (1998) Handbook of Environmental Risk Assessment and Management,
Oxford, UK, Blackwell Science
A comprehensive treatment of the basic principles of environmental
risk assessment and management. Chapters discuss hazard identification,
problem formulation and conceptual model development. Of particular interest
are Chapters 3 (Smrchek & Zeeman), 5
(Seidler et al.) and 7 (Suter).
Department of the Environment/Advisory Committee on Releases to the
Environment (1993) the Regulation and Control of the Deliberate Release
of Genetically Modified Organisms, London, UK, Department of the Environment
Guidance for interpreting the legislation on the release of genetically
modified organisms to the environment.
Department of the Environment/Advisory Committee on Releases to the
Environment (1995) Guidance to the Genetically Modified Organisms (Deliberate
Release) Regulations 1995, London, UK, Department of the Environment
As above.
DETR/Environment Agency (2000) Model Procedures for the Management
of Contaminated Land, CLR 11, London, UK, DETR (in preparation)
the report provides a generic framework for the management of contaminated
land and is aimed at a broad audience. It includes a phased approach to
risk assessment dealing with the qualitative and numerical aspects of
risk assessment in this context with clear links to risk management.
European and Mediterranean Plant Protection Organisation (1994) Decision-making
scheme for the environmental risk assessment of plant protection products;
Terrestrial vertebrates. EPPO Bull, 24, 37-87
An example of the guidelines produced by the European and Mediterranean
Plant Protection Organisation for the ecotoxicological risk assessment
of plant protection products.
Institute of Petroleum (1998) Guidelines for the investigation
and remediation of contaminated retail sites, Colchester, UK, Portland
Press
Guidelines identifying the stages of a site investigation and appropriate
remediation techniques.
Paustenbach DJ (1989) the Risk Assessment of Environmental and
Human Health Hazards: A Textbook of Case Studies, New York, USA, John
Wiley & Sons
A useful collection of case studies that concentrate mainly on
human health risk assessment. there are also some case studies looking
at risks to wildlife.
Presidential/Congressional Commission on Risk Assessment and Risk
Management (1997) Framework for Environmental Health Risk Management
(Final Report), Vol. 1, Washington DC, USA, Presidential/Congressional
Commission on Risk Assessment and Risk Management
Presidential/Congressional Commission on Risk Assessment and Risk Management
(1997) Risk Assessment and Risk Management in Regulatory Decision Making
(Final Report), Vol. 2, Washington DC, USA, Presidential/Congressional
Commission on Risk Assessment and Risk Management
A particularly useful reference in discussing the role and involvement
of stakeholders.
US EPA (1998) Guidelines for Ecological Risk Assessment (EPA/630/R-95/002F),
Washington DC, USA, US Environmental Protection Agency
A recently published document giving useful information on problem
formulation and risk assessment planning from an ecological viewpoint.
Walker CH, Hopkin SP, Sibly RM & Peakall DB (1996) Principles
of Ecotoxicology, London, UK, Taylor & Francis
An excellent textbook covering the fundamentals of ecotoxicology,
including fate and behaviour of chemicals, use of biomarkers, toxicity
testing and discussions on ecotoxicological impacts from the level of
the individual through to the ecosystem, including case studies.
Electronic information sources
DETR internet site - www.dtlr.gov.uk
Environment Agency internet site - www.environment-agency.gov.uk
Health and Safety Executive internet site - www.hse.gov.uk/hsehome.htm
Organisation for Economic Co-operation and Development (OECD) internet site - www.oecd.org/
Society of Environmental Toxicology and Chemistry (SETAC) internet site - www.setac.org/
United Nations Environment Programme, Chemicals Programme internet site - http://irptc.unep.ch/irptc/
Key periodicals
Aquatic Toxicology
Archives of Environmental Contamination and Toxicology
Atmospheric Environment
Chemosphere
Conservation Biology
ENDS Report
Environmental Pollution
Environmental Science and Technology
Ground Water
Journal of Environmental Management
Journal of Environmental Quality
Journal of Toxicology and Environmental Health
Risk Analysis
Water Environment Research
Defra is not responsible for the contents or reliability of the linked web sites and does not necessarily endorse the views expressed within them. Listing should not be taken as endorsement of any kind. We cannot guarantee that these links will work all of the time and we have no control over the availability of the linked pages.
Page published 2 August
2000;
Page last modified
19 September, 2002