Criteria to evaluate whether or not adverse impacts are significant include:
- environmental loss and deterioration;
- social impacts resulting directly or indirectly from environmental change;
- non-conformity with environmental standards, objectives and guidelines; and
- likelihood and acceptability of risk.
Criteria to evaluate adverse impacts on natural resources, ecological functions or designated areas include:
- reductions in species diversity;
- depletion or fragmentation on plant and animal habitat;
- loss of threatened, rare or endangered species;
- impairment of ecological integrity, resilience or health e.g.
- disruption of food chains;
- decline in species population;
- alterations in predator-prey relationships.
Criteria to evaluate the significance of adverse social impacts that result from biophysical changes include:
- threats to human health and safety e.g. from release of persistent and/or toxic chemicals;
- decline in commercially valuable or locally important species or resources e.g. fish, forests and farmland;
- loss of areas or environmental components that have cultural, recreational or aesthetic value;
- displacement of people e.g. by dams and reservoirs;
- disruption of communities by influx of a workforce e.g. during project construction; and
- pressures on services, transportation and infrastructure.
Environmental standards, objectives and targets to evaluate significance include:
- prescribed limits on waste/emission discharges and/or concentrations;
- ambient air and water quality standards established by law or regulations;
- environmental objectives and targets contained in policy and strategy; and
- approved or statutory plans that protect areas or allocate, zone or regulate the use of land and natural resources.
Probability and Acceptance of Risk
Risk-based principles may be used to establish â€˜rules of thumbâ€™ for the acceptability of effects. For example, a statistical threshold of significance may be established to define an acceptable incidence of disease per million people exposed to a specified hazard (e.g. carcinogenic chemical). This approach is often controversial. It is important to document why and how the level and acceptability of risk has been determined.
A risk-based approach can be useful to address the significance of cumulative effects and ecosystem level changes. Typically, a quantitative risk assessment will not be possible because of lack of knowledge of the variability of natural systems. However, qualitative rules of thumb may be set for cumulative loss or change; for example limiting drainage of wetlands to no more than 25 per cent of the area or some other proportion considered to be significant for maintaining their essential functions of flow regulation, aquatic and bird habitat etc.