Employing Site-Specific Sediment Toxicity Tests to Develop Remediation Goals for Polycyclic Aromatic Hydrocarbons at a Manufactured Gas Plant Site

The purpose of this paper is to present a case study of the use of site-specific sediment toxicity data as a line of evidence for development of preliminary remediation goals (PRGs) for the protection of the community of benthic invertebrates in sediments of the Upper Fox River adjacent to the former Oshkosh, WI manufactured gas plant (MGP). Standard 28-d laboratory toxicity tests with the freshwater amphipod, Hyalella azteca, were conducted. Various exposure metrics were examined to determine which metrics were the best predictor of toxicity. Metrics included concentrations of TPAH13 and TPAH34 in sediment (with and without normalization to organic carbon), toxic units (TU) estimated from concentrations of 34 PAHs measured in sediment, and TU estimated from 34 PAHs measured in porewater using passive samplers (with and without the addition of organoclay to avoid fouling of passive samplers). Exposure-response models were used to evaluate the relationships between the various exposure metrics and toxicological responses. All of the exposure metrics provided relatively good fits of models to data and were used to calculate effect concentrations (EC20) predicted to cause 20% reduction in the endpoint (e.g., survival and biomass). The EC20 value of 119 mg/kg TPAH13 was selected for future use as a conservative and protective line of evidence to describe the nature and extent of MGP impacts at the Site. The integrated approach outlined in this study presents a scientifically defensible method for establishing site-specific remediation goals that are protective of benthic communities.