A Low-Impact Delivery System for In-Situ Treatment of Contaminated Sediment

A low-impact delivery system for in-situ treatment if contaminated sediment is proposed. Unlike most conventional delivery systems that rely on injection or mechanical mixing of sediment, the proposed approach make use of natural mixing (bioturbation) processes to work treatment materials into the biologically-active zone. To accomplish this, agglomerates will be developed with the following properties: dense enough to sink through the water column and provide a light non-suffocating layer on the sediment, and able to break down to release active agents over the period of weeks to months. In addition, the binders used for agglomerate must have negligible toxicity. The clear advantages of this over conventional systems are that it targets the biologically active zone where the benthic organisms reside, is less destructive of benthic habitats, can be used to augment Monitored Natural Recovery projects, and can be repeated, as needed, over time. The proposed work involves: a) the development of candidate agglomerates that can bind treatment agents such as activated carbon or valent iron, b) testing the behavior of these in the laboratory (settling behavior, dissolution rate, formation of dusts), and c) observing the efficacy of mixing into sediments in model benthic environments with a single test species (Nereis) and a representative community of mixed benthic invertebrates. To evaluate mixing, a fluorescent trace material will be incorporated into the agglomerate. As the agglomerate is mixed and breaks down, this trace material will be released. The distribution of the trace material within the sediment column will be examined over time (e.g., at one month and two intervals). The sediments and benthic organisms used in the model system will be representative of the Chesapeake Bay costal waters. However, the material being developed will have wide application to both freshwater environments (e.g., as in Lake Hartwell) as well as marine estuarine/marine system such as Hunters Point in San Francisco Bay or the Patapsco River and Baltimore Harbor in Maryland. Application methods that will be considered at a conceptual level for Phase I include a barge-mounted fertilizer spreader and methods currently employed for thin-layer capping.