Critical Review and Reassessment of USEPA’s Risk-Based Cleanup Level for Dioxin and Relocation Plan for the Escambia Superfund Site in Pensacola, Florida. T. C. Bernhardt, D. B. Mathur, G. R. Vishwanath, R. J. Wenning, and D. J. Paustenbach, McLaren/Hart ChemRisk, 1135 Atlantic Avenue, Alameda, CA 94501
The United States Environmental Protection Agency (USEPA) has found that wood-treatment operations at the Escambia Treating Company Site in Pensacola, Florida were responsible for dioxin contamination in residential areas adjacent to the site. Of the various alternatives proposed to address the potential health risks posed by this contamination, the USEPA identified a permanent household relocation plan as the preferred interim action at a cost in excess of $7 million. The USEPA, using highly conservative default assumptions, developed a preliminary remediation goal (PRG) of 0.2 parts per billion (ppb) of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in soil associated with an incremental cancer risk of 10-4 for the site. However, the USEPA adopted TCDD toxic equivalencies (TEQs) instead of TCDD as the basis for the relocation plan. Their decision appears to be inconsistent with health advisories provided by the ATSDR and the CDC. In this study, an alternative PRG for TCDD was developed based on more realistic, stochastic parameters recommended by USEPA. Health risks in residential areas adjacent to the site that were included in the relocation were calculated. Maximum TCDD concentrations in residential areas designated for interim action were compared to the PRGs calculated for the Escambia site; TCDD concentrations in soil were found to be below the 0.2 ppb site-specific USEPA PRG, and significantly below the 1 ppb ATSDR level. The results of this study suggest that TCDD concentrations in the 1 to 10 ppb range in residential soils are not expected to result in any adverse non-cancer health effects or significant cancer risks. Further, the dioxin levels encountered in the most highly contaminated residential areas adjacent to the Escambia site are not expected to pose significant cancer risks. These results suggest that USEPA’s decision to relocate residents located adjacent to the Escambia site was based on several unnecessarily conservative exposure assumptions or other factors not explicitly stated in their decision.