The human health risk assessment (HHRA) process plays an important role in protecting potential human receptors from current and future threats posed by contaminants released into the environment. The proposed approach for the HHRA should be presented to stakeholders early on in the cleanup process to facilitate concurrence.
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The Department of the Navy’s (DON’s) three-tiered HHRA approach closely mirrors the United States Environmental Protection Agency (EPA) Risk Assessment Guidance for Superfund (RAGS) process. The DON HHRA Guidance provides details on what should be included and considered in each tier of an HHRA, discussion on technical issues, and description of tools available to assist in HHRAs. All sites are required to complete a Tier 1 risk assessment. A Tier 2 risk assessment is conducted if the site is found in the Tier 1 evaluation to pose potentially unacceptable risks to human health. If further action is required, a Tier 3 risk evaluation of remedial alternatives is necessary. The key elements of the three-tiered HHRA approach are described below:
Tier 1 includes a screening risk assessment (SRA) to develop the conceptual site model (CSM), identify complete exposure pathways, and evaluate the analytical data to ensure data quality objectives (DQOs) for risk-based screening have been achieved. The SRA compares site maximum chemical concentrations to risk-based concentrations (RBCs). RBCs are concentrations of chemicals in soil, air, and water that are considered protective of human health. The required Tier 1A review results in a list of chemicals that can be eliminated from further consideration and/or a list of chemicals of potential concern (COPCs) based upon a comparison to existing RBCs derived using standard calculations. The optional Tier 1B review involves an SRA conducted using RBCs that are calculated based on site-specific input to determine acceptable concentrations of chemicals in each medium.
The Tier 2 baseline human health risk assessment (BHHRA) incorporates site-specific information to calculate carcinogenic risk and noncarcinogenic health hazard estimates. Only chemicals attributable to a release and not consistent with background levels at the site are carried through for Tier 2 evaluation. A key aspect of the BHHRA is the study design including current and future land use scenarios, data collection and analytical methods, exposure scenarios, exposure concentrations, and the statistical analysis to be used in the risk estimation. The carcinogenic risks and noncarcinogenic hazards calculated in the BHHRA are used to document the magnitude of risk at a site, the primary contributors to that risk, and whether or not a remedial action is necessary at the site.
The Tier 3 risk evaluation of remedial alternatives (RERA) is the evaluation of the remedial alternatives with regards to: (1) the effectiveness of reducing risks to acceptable levels; (2) human health impacts related to remedy implementation; and (3) residual risks that will remain at a site. The purpose of the RERA is to provide remedial project managers (RPMs) with an assessment of the potential short and long-term health risks associated with the remedial alternatives. As part of the RERA process, risk-based preliminary remedial goals (PRGs) are calculated similar to how RBCs are calculated in the Tier 1 SRA, but refined based on the selected remedial actions and site-specific information.
For more information, Chapter 22.214.171.124 of the DON Environmental Restoration Program Manual provides a detailed description of the HHRA approach.