9.4.4 ERA builds upon EIA

Environmental risk assessment addresses three questions.

1 What can go wrong with the project? What impacts might occur to human health and welfare that arise in, or are transmitted through, the environment (i.e., air, water, soil, food, and other plants or animals)? What are some reasonable scenarios (environmental sequences of cause and effect) for the project to result in damage to human health, environment, or equipment (e.g., excess deaths, exceedance of standards, catastrophic accident)?

2 What is the range of magnitude of these adverse consequences? With what frequency might they occur? What historical or empirical evidence is available to judge their likelihood? What data are available on failure rates of processes or components in the project technology?

3 What can be done and at what cost to reduce unacceptable risk and damage? What are the mitigation measures that need to be adopted? What are the costs involved vis-is the benefits derived by implementing these measures?

An EIA answers the first question and usually gives at least a qualitative expression of the magnitude of impacts, while ERA complements and extends the environmental review process. The major additional consideration is frequency of occurrence of adverse effects and how this relates to their magnitude. Risk is evaluated in terms of both frequency and severity (and the level of confidence in quantitative measures of these parameters).