Evaluating the Efficacy of a Low-Impact Delivery System for In Situ Treatment of Sediments Contaminated with Methylmercury and Other Hydrophobic Chemicals

Abstract

This report describes field demonstrations of in situ treatment of PCBs and mercury with activated carbon (AC) delivered using the SediMite® delivery system. The project involved two sites within Canal Creek at the Aberdeen Proving Ground (APG) in Edgewood, Maryland, that are contaminated with mercury and PCBs. The application of SediMite® to a third site—Bailey Creek at Fort Eustis in Virginia—is also described for comparison. Data are also included for a fourth site at which SediMite® was used to treat PCBs within a Phragmites marsh. The sites represent different types of habitats, and the synoptic evaluation provides insights into the performance of SediMite® as a delivery system for in situ treatment with AC across a range of biological and physical conditions. The demonstration projects showed that treatment of PCBs can be carried out in the field using AC delivered via SediMite® . The bioavailability of PCBs was typically reduced by >80% across these sites, with values >90% being achievable. Treatment was also demonstrated for DDx. Efficacy was related to the presence of target doses of activated carbon. Results were equivocal for treatment of mercury. Because most performance metrics for bioavailability rely on laboratory measures of field-collected samples, there is some uncertainty regarding extrapolation to the field. Effects of treatment on native biota were judged to be negligible. This remedial option falls within a range of costs for other remedial alternatives.