On September 29, 2020, the Oregon Department of Environmental Quality (DEQ) released updated guidance on Conducting Ecological Risk Assessments to aid in evaluating ecological risks at contaminated sites and in determining whether, based on those risks, remedial action is required. The guidance identifies circumstances under which ecological risk assessments (ERAs) are necessary during remedial investigations and options for conducting those assessments.

The guidance includes clarifications concerning preliminary scoping and exclusions from the ERA process, which may result in investigation efficiencies at some sites. Additional information on cumulative risk assessment methods may also help to standardize ERAs at sites with multiple contaminants. Finally, in conjunction with the primary ERA guidance document, updated ecological risk-based concentrations (RBCs) for a range of contaminants and exposure pathways can be found in DEQ's Tables and Appendices for: Conducting Ecological Risk Assessments. The ecological RBCs set default values for acceptable risk levels, and practitioners should review these closely to determine if the changes may affect the need for remedial action at specific sites.

When conducting ERAs, reference also should be made to companion guidance on Decision Unit Characterization. DEQ is treating the ERA guidance as a living document and has requested ongoing feedback from stakeholders.

Key issues addressed in the ERA guidance include:

• Scoping the ERA. As a preliminary step, scoping involves the assembly of basic information to describe ecological features and species at the site, and evaluates the potential for complete exposure pathways for ecological receptors. Scoping is essential to determine if an ERA is needed. For simple sites where ecological exposures are unlikely, a screening checklist may be employed for scoping. For all other sites, a more rigorous exposure pathway assessment should be conducted in accordance with the conservative methods set forth in the guidance. If the scoping identifies complete exposure pathways and there are no applicable exclusions, an ERA is required. 

• ERA exclusions. ERAs will not be required when the “de minimis size of the site results in a low potential for meaningful exposure.” The size exclusion is available if sites have less than 0.5 acres of exposure area, the area adjacent to the site must not contain a terrestrial exposure area greater than 0.5 acres, and if threatened and endangered species and their critical habitat are not present within 1/4 mile of the site boundary. However, exclusions do not apply for “aquatic and sensitive environments,” “areas where threatened or endangered … species are likely” to occur, and “areas where high concentrations of contaminants are known or suspected to be present that could represent acute toxicity or an ongoing source to other environments.”​​​​​​ 

• Risk assessment methods. DEQ follows EPA’s standard ERA process to determine whether the site poses an unacceptable ecological risk. For simple sites, a Tier I screening-level risk assessment, which compares contamination concentrations to default ecological RBCs developed by DEQ, may be appropriate. Tier II screening allows for site-specific adjustments to the RBCs, such as bioaccumulation factors, organic carbon, or prey consumption rates. If adjustments are made, the basis for the adjustments must be documented. Tier III ERAs are more complex than the standard screening frameworks and “use additional endpoints to complete the risk assessment for site-specific receptors.” Importantly, Tier III methods must be approved by DEQ for each site. ​​​​

• Updated ecological RBCs. The guidance includes updated ecological RBCs tables to use, or adjust for use, in the risk assessments. RBCs “are receptor- and media-specific concentrations that represent acceptable risk to plants, invertebrates, fish, birds, and mammals within terrestrial and aquatic environments.” However, updates to sediment RBCs were not completed for the new guidance.

• Cumulative risk assessments. Because contaminated sites often include multiple contaminants, the guidance clarifies approaches for estimating the cumulative risks from exposure to all relevant contamination. 

The updated ERA guidance should be consulted by contaminated site practitioners in Oregon. The clarifications to the ERA scoping process and exclusions for terrestrial ecological evaluations may provide opportunities to streamline site investigations. The updated ecological RBCs will be relevant to determining whether remedial action at contaminated sites is required to protect potential ecological receptors from adverse effects. Finally, the detailed content on completing basic cumulative risk assessments may standardize the analysis of ecological risks from multiple contaminant exposures.