The main features of exposure assessment and health impact characterization in an EIA study is that exposures to the health-impact causing agents and their subsequent health effects must be determined for the no action alternative (the project is not implemented) and the proposed action and its alternatives. Thus, the health effects characterized for the no action alternative provide the baseline condition against which the health effects characterized for the proposed action and its alternatives can be compared. The information obtained during the description of the project and the environment is critical to these steps. An important consideration in assessing exposures within the EIA process is that many of the methods, tools and techniques used to predict other biophysical environmental impacts may be used to determine exposure to health impact-causing agents.