How to deal with the adverse effects of contaminated megasites
Risk management theories
There are many approaches to the general concept of ‘risk’, depending on the mental frames they are used in. Relevant for IMS are three mental frames:
- Risks in the environmental discourse, where it is defined as the chance of adverse effects on human health, ecosystem damage and contamination of resources like drinking water;
- Risks in the discourse of management control cycle, where risk is defined as losing control over the system in such a way that effects will be unpredictable;
- Risks in the socio-economic discourse, where it is defined as the adverse effect on the socio-economic system, like unemployment, unwillingness to invest, high costs of remediation, psychological effects, etc.
The first category of risks is the main focus of the IMS. Section 2 is about the risk-assessment, using a model of human exposure to contaminants, a model for ecosystem damage and a water quality evaluation model.
The second category of risks is implicitely part of section 4, where the management control is described.
The third category of risks plays an important role in stakeholder processes, choices and decisions. For many stakeholders the threat of soil and groundwater contamination is related to other threats. In economically prosperous regions, where people have incomes and a general feeling of safety, concern over environmental threats is more prominent than in regions where basic life is the main focus.
The cognitive basis for risk assessment
The concept of ‘risk’ is based on the comparison of the present state of the environment with an imagined adverse state of the environment. This adverse state will have negative impacts on human interests. The probability that this imagined adverse state will occur leads to an estimate of the chance that this adverse state actually will occur. Data are collected to assess the present state. In many risk assessments however, the criteria to evaluate the chances of adverse effects does not come from the present state but from a desired state. When water of a moderate quality is accepted in the present state and a small part is polluted, people will often choose remediation targets coming from clean water criteria instead of criteria for the moderate, but acceptable quality.
At the moment, a variant of this conceptual model is taken into further development in the so-called DPSIR methodology. With:
- D = Driving forces
- P = Pressures
- S = State
- I = Impact
- R = Response
- A status document can be downloaded under "Download files".
Risk assessment in the IMS deals with all aspects of this general risk concept. In risk assessments of small contaminated sites, criteria and the estimate of chances of adverse effects could be generalized, because the costs of a tailor-made approach are higher than the remediation costs. In megasites it is the other way around. Costs of remediation is much higher than the costs of a tailor-made risk assessment.
The human exposure model
The human exposure model is based on the general risk assessment concept. The adverse state is fixed and defined as the situation where humans are exposed to toxic substances with illness and ultimately death of human beings as adverse effects. The desired state is also fixed and defined as ‘not exposed to toxic levels that are known to cause sickness’. These levels are set for the most common toxic substances and known as the Acceptable Daily Intake (ADI). The dynamic part of human exposure models deals with the pathways from the contaminated soil and groundwater to the human body. These pathways are quantified, using data and the model. By using default values the model can be used to give a rough estimate of human exposure to a known contamination. When more data are available, default values in the model could be made more precise and some pathways could be validated, resulting in a more accurate description of the risk of human exposure.
The risk assessment in IMS is also based on the human exposure model. However, there are some specific problems in megasites that need special attention:
- The assumption that mere exposure to certain levels of toxic substances - originating from soil contamination - leads to the adverse state of health problems should be re-evaluated. Being an industrial area, it is quite possible that exposure to the same toxicants could come from other sources, using the same pathways. In that case it could be questioned whether cutting off the pathways from the soil contamination to human beings will give a (significant)positive effect on human health.
- In a megasite the data on the present state of the contamination will be limited, at least in the beginning. In that stage the model could be very inaccurate.
- Because a megasite has a large contaminated area, it is more difficult to define the pathways. It depends on the behaviour of the people involved and the variability of the contamination which pathways are relevant at a certain moment.
The IMS therefore has a tiered approach in the risk assessment. On the first level in section 1, the model will run on many default values and a limited set of data. It will give an indication of which pathways are critical under which conditions rather than an indication of the actual risks involved. On the next levels, in section 2, more data will lead to further insight into the relevant pathways and to a more accurate estimate of the risks. This process could go on until stakeholders are satisfied with the accuracy of the risk assessment, taking the additional costs to reach a higher degree of accuracy into account.
The ecological impact model
In the Netherlands in the late 1980s early 1990s there was an attempt to adapt the human exposure model to ecosystems. With a kind of ‘Acceptable Daily Intake value for the ecosystem’ the same source-pathway-target approach could be applicable. But whereas the ADI was generally accepted for humans, comparable values for ecosystems were rejected as not representing accurately enough the adverse state of the ecosystems, resulting in basic discussions between authorities and industries about the definition of an ecosystem, the value of nature reserves and the methods for measuring adverse effects, like bioassays. With no general accepted definition of the adverse state of ecosystems, nor the desired state of ecosystems, it was impossible to define a method.
Recently another approach was proposed, under the name of Periscope. It was built on the older Triade approach. This approach aims to optimise the estimation of actual ecological effects in a specific area or ecosystem by gathering multiple pieces of evidence along various ways. The TRIAD includes three pillars consisting of a chemical, toxicological and ecological assessment. Each pillar of the TRIAD can be extended over three tiers, representing low, middle and high levels of sophistication. Where the TRIAD was developed in natural environments like river basins, it needed an additional step before it could be applied in industrial areas. This step is the definition of the ‘system’, and the adverse state and desired state of this ecosystem. This definition is a matter of choice by the stakeholder group, advised by experts. The desired state could be defined by choosing a referential ecosystem, comparable with the ecosystem in or next to the Megasite, but uncontaminated. The TRIAD approach will be used to evaluate the aspects of the ecosystem that makes the difference between desired and adverse quality. By monitoring the interventions, improvements in the quality of the ecosystems will be monitored.
This approach could lead to the stakeholders deciding that the difference between the desired and adverse ecosystem quality related to soil contamination is too small to be relevant. To make this decision it is important that all relevant stakeholders are present.
Risks and groundwater control
The knowledge of the groundwater system results in a thorough description of the present state and a fair insight into the future state. The problem with the risk assessment of groundwater contamination is the definition of the desired state and adverse state. Many countries have legislation where ‘clean groundwater’ and the ‘stand still principle’ are the basis of the definition of the desired state, without using the knowledge of the groundwater system to specify this. From this point of view, the adverse state is the mere fact of moving bodies of contaminated water and the adverse effect is clean water that is becoming contaminated at a specific time and in a specific place, which ignores the fact that all groundwater systems are dynamic.
In the IMS special attention is given to the site-specific definition of the desired and adverse state of the groundwater system. Adverse effects are compared to the present state of system and this assessment is the basis for the composition of the scenarios.
