Techniques for Reducing Contaminant Release during Dredging Operations

Dredging practices in the United States have evolved primarily to achieve the greatest possible economic returns through maximizing production. Recently, more consideration has been given to environmental impacts because various Federal and State regulatory agencies have implemented restrictions on the dredging cleanup activities. Conventional dredges are not specifically designed or intended for use in dredging highly contaminated material. However, dredges are the logical, and perhaps only, means of removing contaminated sediments that may be found in the Nation's waterways. Some modification to equipment and/or dredging techniques could result in their use for that purpose with minimal adverse impact on the environment. In some instances special dredges may be needed for cleanup activities. The Corps of Engineers has initiated research to develop a method for predicting resuspension and release of contaminants using various types of dredging equipment and techniques and to improve and/or develop new equipment and techniques for dredging highly contaminated sediments. The investigation includes an evaluation of the resuspension of solids and potentially toxic constituents in the immediate vicinity of operating cutterheads, dragheads, and clamshells. Because the environmental impact associated with each type of dredge and dredging technique is directly related to the dynamics of the dredging operation, in situ sampling systems are being used when possible. A dredging demonstration on the James River, Virginia, compared the performance of a conventional cutterhead and a modified dustpan dredge operating in sediments contaminated with Kepone. Demonstrations comparing performance of conventional and watertight clamshell buckets were conducted in the Tampa, Florida area. These will be used as case studies to illustrate the advantages of various equipment types for dredging contaminated sediments.