In-situ Sorbent Amendments: A New Direction in Contaminated Sediment Management

A sediments form the ultimate repositories of past and ongoing discharges of hydrophobic organic compounds (HOCs) such as polychlorinated biphenyls (PCBs), many pesticides, and dioxins, as well as mercury (Hg) and methylmercury (MeHg). These sediment-bound pollutants serve as longterm exposure sources to aquatic ecosystems. Approximately 10% of the sediment underlying the United States' surface water is sufficiently contaminated with toxic pollutants to pose potential risks to fish and fish-eating wildlife and humans. Remediation of contaminated sediments remains a technological challenge. Traditional approaches do not always achieve risk reduction goals for human health and ecosystem protection and can even be destructive for natural resources. Though removal of contaminated sediment by dredging and disposal in a secure landfill can be effective under certain conditions, a recent study by the National Research Council found a wide range of outcomes. Among the problems with dredging are unfavorable site conditions, resuspension of contaminated sediment into the water column, and contaminated sediment residuals. While capping contaminated sediment with clean sand may be a viable remedial option at some sites, often the alteration of sediment bathymetry may not be acceptable and the control of contaminant transport through the cap can be a challenge. In addition, both dredging and conventional capping result in the destruction of existing benthic ecosystems. Therefore, development of new techniques offering greater flexibility in contaminated sediment management and avoiding some of the problems with conventional dredging and capping is highly desirable. This feature article summarizes research by several groups in the U.S. and Europe to develop a novel approach for in situ sediment remediation that minimizes or eliminates some of the problems with traditional technologies. The efforts involve introducing sorbent amendments into contaminated sediments that alter sediment geochemistry, increase contaminant binding, and reduce contaminant exposure risks to people and the environment. We present here a description of recently concluded laboratory studies and a brief outline of ongoing pilot-scale trials, field challenges, regulatory issues, and further research needs.