Ecological risk occurs when a contaminant is in contact with any part of the ecosystem long enough and at a level that is able to cause an adverse effect. It is important to include stakeholders early on in the ecological risk assessment (ERA) process to identify the appropriate assessment endpoints and ecotoxicity benchmarks. If natural resources are potentially impacted by releases at a site, then the designated natural resource trustees should be included as well.
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The three-tiered ERA approach closely mirrors the United States Environmental Protection Agency (EPA’s) eight-step process defined in the Ecological Risk Assessment Guidance for Superfund (ERAGS): Process for Designing and Conducting Ecological Risk Assessments. The Department of the Navy (DON) ERA Guidance provides details on what should be included and considered in each tier of an ERA, discussion on technical issues, and description of tools available to assist in the completion of ERAs. The key elements of the three-tiered ERA approach are described below:
- The Tier 1 screening ecological risk assessment (SERA) is conducted to identify chemicals of potential concern (COPCs) that may pose unacceptable risks to the environment, thus focusing efforts on those constituents most likely to drive ecological risks. The Tier 1 SERA is usually conducted during the SI phase using existing data and conservative assumptions. The evaluation consists of two steps as follows:
Step 1 includes conducting a site visit, identifying site-specific data needs (e.g., site chemical data, ecotoxicity), identification of assessment endpoints and representative receptors (e.g., surrogate species), determination of complete exposure pathways, and refinement of the conceptual site model (CSM).
Step 2 includes calculating an exposure point concentration based on the CSM and characterizing risk through the use of hazard quotients. For each receptor/COPC combination having a complete exposure pathway, the maximum concentration detected is compared to the appropriate ecotoxicity benchmark using the hazard quotient approach.
Chemical constituents having maximum concentrations that are below their benchmark are eliminated. If there are no unacceptable ecological risks or no complete exposure pathways to all ecological receptors, the site may be closed out for ecological concerns and exit the ERA process. If the SERA demonstrates that potential exposure pathways and unacceptable risk may exist, an interim action can be taken and/or a Tier 2 evaluation initiated.
- The Tier 2 baseline ecological risk assessment (BERA) is intended to be a more rigorous evaluation. Rather than relying on conservative assumptions and comparison to ecotoxicity benchmarks, Tier 2 incorporates site-specific information to calculate risk estimates for those COPCs posing potential risk in the Tier 1 SRA. The Tier 2 evaluation also screens out constituents that are consistent with background concentrations. The BERA is comprised of the problem formulation, study design and data quality objectives (DQOs), verification of the field sampling design, site investigation and analysis, and risk characterization. Planning for these activities involves extensive communication between DON, regulators, natural resource trustees, and other stakeholders. The BERA will characterize the ecological risk posed by the site as documented in the RI report. A risk management decision is made to determine either no further action (NFA) from an ecological perspective or if the site is found to pose an unacceptable ecological risk then remedial alternative development (including a Tier 3 risk evaluation) is appropriate.
- The Tier 3 risk evaluation of remedial alternatives (RERA) for ecological receptors is an evaluation of the remedial alternatives with regards to: (1) the effectiveness of reducing risks to acceptable levels; (2) ecological 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.
For more information, Chapter 126.96.36.199 of the DON Environmental Restoration Program Manual provides a detailed description of the ERA approach.