Contaminated Sediments – Dredging and Dredged Sediment Disposal

Each year several million cubic yards of sediment are dredged in order to maintain and enhance channel depth in many navigable waters of the US. Since aquatic sediments tend to accumulate a variety of chemical constituents that represent potential threats to water quality, there is concern that contaminants associated with those sediments may be released to the water at dredging and/or dredged sediment disposal sites in open water or on land.

Dr. Lee first became involved in evaluating the water quality significance of contaminants in dredged sediments in the 1960s. In the 1970s he directed more than a million dollars in research on the environmental quality impacts of dredging and dredged sediment disposal as part of the US Army Corps of Engineers Waterways Experiment Station’s $30-million, 5-year Dredged Material Research Program (DMRP) designed to evaluate the potential environmental quality impacts of the open water disposal of contaminated dredged sediment. That work, conducted by Dr. Lee and his associates, including Dr. Jones-Lee, was focused on developing criteria for the open water disposal of contaminated dredged sediment, and included extensive, coordinated field and laboratory investigation of the release and impact of about 30 chemical contaminants (including heavy metals, chlorinated hydrocarbon pesticides, PCBs, aquatic plant nutrients, ammonia, and oxygen-demanding substances) from dredged sediment at about 100 urban/industrial waterway areas throughout the US. Their work revealed the unreliability of total concentrations of contaminants in sediment as a basis for assessing the impact of sediment-associated contaminants on aquatic life. They field-evaluated the elutriate test and associated toxicity tests for making such assessments. The results of those studies were more recently summarized and updated in Lee and Jones-Lee (2000) and Jones-Lee and Lee (2005).

There is considerable interest today in developing sediment quality criteria for regulating contaminants in sediments, including dredged sediment; several approaches have been proposed for the evaluation of the water quality significance of chemical constituents in aquatic sediments. While chemical-concentration-based approaches, such as equilibrium partitioning and co-occurrence, are being used, such approaches are unreliable in their assessment of the water quality significance of chemicals in aquatic sediments. As Lee and Jones-Lee have discussed in several publications, this is to be expected because they do not reliably consider the aquatic chemistry and aquatic toxicology of the sediment-associated contaminants. Drs. Lee and Jones-Lee have published considerably on the technical issues of impacts of sediment-associated contaminants including factors that affect the availability of such contaminants. Their writings discuss many of the reasons that chemical-concentration-based approaches are not reliable for estimating sediment toxicity or bioaccumulation of sediment-associated chemicals into aquatic life. They recommend that biological effects-based approaches (sediment toxicity and actual bioaccumulation) be used.

Dr. Lee has been active since the mid-1970s in expressing technical concerns about the potential environmental impacts of upland disposal of contaminated dredged sediments. In general, it has been his experience that while often presumed to be a "safer" alternative for dredged sediment disposal, upland disposal of contaminated dredged sediments can lead to pollution of surface and/or groundwaters by contaminants in the dredged sediments. He has substantial experience in evaluating the potential public health and environmental quality impacts of on-land disposal of wastes which in many respects are similar to those associated with disposal of contaminated dredged sediment on land.

Drs. Lee and Jones-Lee have an extensive set of publications on this topic. Further information on their activities in this area and on obtaining copies of their publications is available upon request.

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