Assessing RiskFeedback

A site revitalization project should include an assessment of the human health (and, in some cases, ecological) risks that may result from exposure to hazardous substances present in environmental media. The necessity of land use restrictions and/or environmental remediation are evaluated on the basis of a risk assessment. This overview will provide a high-level orientation to EPA's risk assessment process for supporting environmental management decisions. The following subsections will present a discussion of existing and emerging risk assessment methodologies pertaining to the main components of a human health risk assessment, as well as a risk calculation tool to enable a user to investigate the potential risks associated with various types of land use scenarios at a particular site.

The principal EPA guidance document for conducting a human health risk assessment for a contaminated site is Risk Assessment Guidance for Superfund, Human Health Evaluation Manual, Part A, Interim Final . As stated in the Introduction of this guidance, the objectives of the human health evaluation process are to:

These objectives, particularly the first three, are focused towards an evaluation of potential future exposures, rather than an evaluation of the significance of current or historical exposures. Thus, a risk assessment is used to estimate whether potential current and future chemical exposures might pose health risks to individuals within a broad population in the absence of further remediation. In concert with an EPA risk assessment, the Agency for Toxic Substances and Disease Registry (ATSDR) may conduct a public health assessment to determine if people have been or are currently being exposed to harmful levels of hazardous substances. Depending on the outcome of the public health assessment, ATSDR may conduct further studies of health effects, such as conducting biological monitoring of community members or investigating the prevalence of one or more diseases. The role of ATSDR and other organizations in protecting public health in areas outside the scope of the human health risk assessment process is described in the Public Health section.

The focus of this risk assessment section in SMARTe is human health risk assessment because the great majority of Brownfields projects are primarily geared towards revitalization of sites in an urban and/or industrial setting. However, EPA also publishes guidance for conducting ecological risk assessments, and many of the concepts described in this section are also relevant to ecological assessments. The need for ecological risk assessment in supporting environmental management decisions may be identified in Future Land Use should potential uses include options for providing wildlife habitat.

Estimating the hazards posed by toxic chemicals in the environment commonly involves the efforts of a multidisciplinary team that may include toxicologists, chemists, statisticians, hydrogeologists, and engineers. In order to focus the efforts of these individuals throughout the site characterization and assessment process, and ensure that this process efficiently supports risk management decisions, a dynamic conceptual site model (CSM) is essential. The CSM integrates key information relating to the nature and extent of contamination, the fate and transport of hazardous substances in the environment, and the ways in which people may be exposed to these substances. Because a number of pollutants and affected media are often identified in the CSM, the focus of EPA risk assessment has shifted over time from the potential impact of a single pollutant identified in one environmental medium to integrated assessments involving suites of pollutants in different media and multiple exposure pathways leading from these media to various human receptors.

EPA risk assessments employ a four-step process for systematically quantifying possible human health risks. Each of these steps in a risk assessment is the subject of discussion in a subsection, with links to relevant guidance documents and other useful information. The four steps include:

These steps are depicted in the figure below (cf, Risk Assessment Guidance for Superfund, Human Health Evaluation Manual, Part A, Interim Final)