Guidance through a risky business

Businesses take and manage risks to survive in a competitive market place. Like all organisations, they have to manage risks from hazards such as competition in the market, from fluctuations in demand for goods and services, from skill shortages and from damaged reputations. On the environmental side, they may be exposed to risks from historical land acquisitions, inherited safety cultures or through non-compliant, albeit accidental environmental releases. Risk ‘profiling’ has become essential to good corporate governance and a pre-requisite for sound ethical, social and operational (including environmental) management. Most large corporations have risk management committees reporting periodically to the Board and management systems that identify unacceptable risks and specify accountabilities for their management.

Environmental risk is of concern because of the liabilities that may accrue and the damaged customer reputation that can result from the potential or actual harm caused to the environment. Businesses operate in a highly regulated environment with regulatory decisions being made by close reference to the statutory duties and powers of the regulator and the responsibilities of operators. One aspect of regulatory work is the issuing, drafting and enforcement of environmental permits allowing business to discharge to, or abstract from the environment. This is where most environmental professionals first encounter the requirement for an environmental risk assessment because the environment agencies often require an assessment of risk to inform the environmental permitting of industrial activities.
Environmental risk assessments are a feature of many permitted operations.

In England and Wales, the Environment Agency promotes consistency in the risk assessments that inform its decisions through implementation of Government Guidelines on Environmental Risk Assessment and Management to relevant activities. These were revised in 2000, with the Department for Environment, Food and Rural Affairs (Defra) re-endorsing their use in 2002. Clear problem definition, use of a tiered approach to assessing risk, the principles of proportionality and consistency of use, the explicit treatment of uncertainty and the need for presentational transparency are common themes in the revised guidelines, referred to as Green Leaves II. The guidance provides a risk management framework to which specific risk guidance, such as that for waste management regulation, historically contaminated land, groundwater protection and major accident hazards, for example, can refer.

The most recent proposed application of the guidelines relates to waste management. The tiered approach is being promoted by Defra in support of a proportionate system for waste regulation for individual waste disposal and recovery operations. This is welcome and appropriate given the sector is rapidly becoming a ‘process’ industry with increased treatment of wastes prior to disposal and the co-location of waste processing technologies at single sites, also often for resource recovery and residuals management.

Processes such as in-vessel composting, the thermal processing of clinical waste, the stabilisation/fixation of hazardous wastes, biomass gasification, sludge combustion and the use of wastes as supplementary fuel, present operators and regulators with new challenges as to their safe and environmentally responsible operation. A further feature is the increased regulatory emphasis on public and ecosystem health, and of the need for the formalised assessment of risks to these from waste installations. Public confidence in waste management installations, secured through enforcement of the planning and permitting regimes and sound operational performance, is central to establishing the new technologies expected to come on-stream and well-informed risk management plays a critical role in securing this confidence.

The waste management sector already applies risk assessment widely to issues such as the potential long-term risks to groundwater from landfills, the potential risks to human health from incinerator stack emissions and more recently, the potential health impacts from landfill gas. The development of site conceptual models, site-specific exposure scenarios and the application of the ‘source-pathway-receptor approach’, supported by quantitative analysis where appropriate, has become commonplace. Many risk tools are based upon environmental models that characterise pollutant pathways in open environmental systems and assume (or sometimes model) prior release of the source term to the environment through mechanisms such as progressive liner failure, point source release or advection or diffusive flow through a capped landfill.

Risk assessment tools have been developed at a range of levels of technical sophistication and, in deciding on the application of risk assessment, risk analysts need to consider both (i) the appropriate risk assessment tool by reference to the type of risk being studied (the risk of undesirable initiating events, of environmental exposure following release or environmental harm following exposure) and (ii) an appropriate level of sophistication for the risk tool selected as needs, complexities, priorities and data allow. Much of the waste processing that occurs now takes place in engineered systems, often applying linked unit processes. Here, mass balances are conventionally represented by process flowsheets. The performance of (and risks from) unit processes can be directly assessed using fault and event tree analysis (ETA). These tools, used widely in the chemical, oil and water sectors are increasingly being applied to waste process flowsheets.

Fault and event tree analyses are used for assessing process failures and subsequent consequences of undesirable initial events, usually from engineered containment or unit processes. Fault tree analyses select an undesired event (such as an engineering failure, a fire or an inadvertent mixing of incompatible wastes) and trace it back to the possible causes, which can be component failures, human errors or other factors that may lead to the fault. Logic relationships (i.e. and/or ‘gates’) allow the root causes of the failure of the system to be combined and quantitative analysis involves an assignment of conditional probabilities to the various failure modes, where failure data is available. Event tree analysis starts with the initiating event (the failure of a leachate treatment system) and is used to follow the onward consequences of a release. As with many risk techniques, fault and event tree analyses require data to quantify the contributory causes, though both may be used qualitatively.

The requirements of the EC Landfill Directive on waste pre-treatment, a growth in process technology for waste pre-treatment and the requirement under PPC to assess the risks of accidents and their consequences, can be expected to encourage a greater use of these tools for assessing the potential causes and frequencies of process failures (e.g. leachate treatment, gas collection or gas combustion failures) in regulatory assessments, and for assessing the risks from the combination of hazards, such as from flooding at waste management installations. Progressing beyond unit processes to open environmental systems inevitably necessitates the application of distribution models. Human health and ‘amenity’ risk assessments that assess the impacts of emissions, dusts and odours downwind of operating facilities, for example, are increasingly required. Many treatment processes such as windrow composting and the bioremediation of organic wastes may emit odours, bioaerosols and/or volatiles.

These risks need to account for the significance of impacts at the receptor using exposure models to define permissible emission limits at the source. As with noise limit models, approaches attempt to define maximum permissible levels of exposure by considering the existing baseline of impacts from other sources as well as the compound effect of exposure and time. Figure 2 illustrates this type of assessment used in support of an environmental statement, where percentile odour unit values are specified.

While there has been considerable development in the application of environmental exposure assessment to waste facilities, there remains a need to consider the total mass balance of waste systems and account for total losses, so that the totality of the impacts are assessed (and regulated) rather than attention inadvertently being paid to a single component of the system. The impact on groundwater of new landfill development rarely assesses the other routes that contaminants might take, such as flows to a treatment plant, volatile emissions to the atmosphere, or discharges to surface water. The singular approach historically adopted by many risk assessments has been in response to specific regulation, but in future, risk assessments for waste installations may need to adopt a more ‘holistic’ approach, that views potential impacts more closely by reference to multimedia (air, water, land, biota) routes of exposure and to a wider range of receptors within the environmental setting.

Ultimately, for environmental receptors, the risk of potential environmental harm following an environmental release (accidental or consented) and a subsequent exposure is characterised by the dose-response relationship. This describes the relationship between the intake of a hazardous agent and its toxicological effect on the receptor. The requirements of the EC Seveso II (COMAH) Directive to large waste management installations and of the EC Habitats Directive to licensed facilities act, in part, as regulatory drivers for a broadening of the emphasis of risk management to the receptor components of the system. Furthermore, changes in the potential sensitivity of the human population have given rise to a greater awareness of vulnerable populations. The emphasis in these assessments is on assessing the significance of potential harm at the receptor and evaluating what constitutes significant damage to the receptor of concern. This is not trivial and for ecosystems in particular, there is a wide ranging debate over the level at which serious impairment to ecosystem function should be assessed.
The future for risk analysis applied to waste management installations is likely to focus increasingly on assessing an expanded set of hazardous circumstances and on the integration of risks that have historically been assessed in isolation

Whilst this is to be welcomed, its implementation will raise a number of technical and practical challenges for risk analysts, operator and regulators, including: