A Human Health Risk Assessment (HHRA) is the process that evaluates the likelihood that adverse health effects are occurring or may occur as the result of exposure by humans to one or more stressors by one or more exposure pathways. In CERCLA or RCRA Corrective Action, HHRA is used specifically to mean a qualitative and/or quantitative evaluation of the actual or potential impacts of contaminants from hazardous waste sites on human receptors. There are several classes of human receptors, based on age, gender, and include special populations such as the immunocompromised. For risk to human health to exist, the contaminant must have the ability to cause an adverse effect and it must co-occur with or contact a person long enough and at a strong enough intensity to cause the adverse effect.