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US-EPA’s guidance for developing pore water-based sediment remediation goals to protect benthic organisms
Citation:
Burkhard, L., Dave Mount, AND R. Burgess. US-EPA’s guidance for developing pore water-based sediment remediation goals to protect benthic organisms. Conference on Remediation and Management of Contaminated Sediments, New Orleans, LA, February 11 - 14, 2019.
Impact/Purpose:
A methodology for developing sediment remedial goals (RGs) based upon concentrations of chemicals in sediment pore water has been developed. Superfund requested the methodology and the methodology, based upon passive sampling measurements, incorporates contaminant bioavailability into the RGs. In general, it is believed that by incorporating bioavailability measurements into RGs, site remediation activities could be completed faster and with lower costs. Superfund (OLEM-OSRTI), Great Lakes National Program Office (GLNPO), and state regulatory agencies can use this methodology at their contaminated sediment sites. The methodology document was developed under SHC Contaminated Sites Project 3.61, Contaminated Sediment Task #3 research plan.
Description:
Background/Objectives. In the past decade, passive sampling methods have undergone extensive development and the technique is now being applied at many Superfund sites to measure concentrations of freely dissolved chemical in the water column and sediment pore waters. If ecological risks are assessed based on contaminant concentrations in pore water, methods for translating these measurements into remedial goals are needed. EPA recently developed a guidance methodology for deriving pore water remedial goals (PWRGs) for sediments contaminated with non-ionic organic chemicals to protect benthic organisms from direct-toxicity (EPA 600/R-15/289). Approach/Activities. The guidance methodology is integrated into Superfund’s eight-step Ecological Risk Assessment (ERA) process. In the Screening Level (Steps 1 & 2) where the nature and extent of contamination is characterized, the organic carbon content (fOC) and bulk chemicals of concern (COC) concentrations (ìg/kg-dw) are measured. With these data, organic carbon normalized contaminant concentrations (ìg/kg-OC) are computed, then divided by EPA’s Equilibrium Partitioning Sediment Benchmarks (ESBs) to compute the toxic units (TUs) for the COCs. In the Site Investigation (Step 6), sediments with total TUs greater than 1.0 are passively sampled. In the Risk Characterization (Step 7), TUs are computed using the Final Chronic Value (FCV) from EPA’s water quality criteria (i.e., freely dissolved concentrations in pore water are divided by the FCV for the COC). Total TUs greater than 1.0 indicate benthic risks are present. For sediments with unacceptable risks, one would move on to Risk Management (Step 8) where remedial goals are developed. Remedial goals can be expressed on a bulk concentration basis (ìg/kg-dw), organic carbon normalized basis (ìg/kg-OC), or free dissolved chemical concentration basis (ìg/L). Results/Lessons Learned. The methodology and its scientific underpinnings will be provided along with an illustrative example. Consistency between passive sampling measurements and sediment toxicity test results is important in applying this methodology. When consistency is demonstrated, one can be reasonably assured that the causes of toxicity to benthic organisms in the sediment have been correctly identified and that the developed pore water remedial goals for the toxicants will be protective of the benthic organisms at the site.