In figure 7-2 below, the elements of mitigation are organised into a hierarchy of actions:
- first, avoid adverse impacts as far as possible by use of preventative measures;
- second, minimise or reduce adverse impacts to â€˜as low as practicableâ€™ levels; and
- third, remedy or compensate for adverse residual impacts, which are unavoidable and cannot be reduced further.
Key principles for the application of mitigation consistent with the above framework include the following:
- give preference to avoid and prevent measures;
- consider feasible alternatives to the proposal and identify the best practicable environmental option;
- identify customised measures to minimise each of the main impacts predicted;
- ensure they are appropriate, environmentally sound and cost-effective; and
- use compensation or remedial measures as a last resort.
EIA good practice in mitigation requires a relevant technical understanding of the issues and the measures that work in the circumstances.
Mitigation can be carried out by:
- structural measures, such as design or location changes, engineering modifications and landscape or site treatment; and
- non-structural measures, such as economic incentives, legal, institutional and policy instruments, provision of community services and training and capacity building.
Structural measures are well established for certain types of projects, such as dams, roads, and oil and gas exploration and development. In some cases, industry codes of good practice will be available. However, these need to be applied with regard to the nature and severity of environmental impacts; for example taking account of nearby protected areas, patterns of wildlife mitigation or constraints imposed by natural hazards. Other projects involving new technology may require non-standardised or even untried measures to mitigate the adverse impacts. These need to be given special attention during impact management.
Non-structural measures are used increasingly. They can be applied to reinforce or supplement structural measures or to address specific impacts. For example, many types of social, community and health impacts are addressed by non-structural measures and their use is becoming broader.
A three-step process of mitigation can be applied to relate the hierarchy of elements in Figure 1 to the stages of the EIA process when they are typically applied. Generally, as project design becomes more detailed, the opportunities for impact avoidance narrow and the concern is to minimise and compensate for unavoidable impacts. However, these distinctions are not rigid and opportunities for creative mitigation should be sought at all stages of EIA and project planning.
Step One: Impact avoidance. This step is most effective when applied at an early stage of project planning. It can be achieved by:
- not undertaking certain projects or elements that could result in adverse impacts;
- avoiding areas that are environmentally sensitive; and
- putting in place preventative measures to stop adverse impacts from occurring, for example, release of water from a reservoir to maintain a fisheries regime.
Step Two: Impact minimisation. This step is usually taken during impact identification and prediction to limit or reduce the degree, extent, magnitude, or duration of adverse impacts. It can be achieved by:
- scaling down or relocating the proposal;
- redesigning elements of the project; and
- taking supplementary measures to manage the impacts
Step Three: Impact compensation. This step is usually applied to remedy unavoidable residual adverse impacts. It can be achieved by:
- rehabilitation of the affected site or environment, for example, by habitat enhancement and restocking fish;
- restoration of the affected site or environment to its previous state or better, as typically required for mine sites, forestry roads and seismic lines; and
- replacement of the same resource values at another location, for example, by wetland engineering to provide an equivalent area to that lost to drainage or infill.