Each year, between 3 and 5 million cubic yards of sediments are dredged from the Great Lakes by the Corps, private industry, municipal and private marinas, utilities and others. This page will provide an overview of the options available for managing dredged material, which include:
Open water placement involves the discharge of dredged material directly to the lake or river. Hydraulically dredged material may be discharged by pipeline a short distance offshore. Mechanically dredged material may be placed in bottom-dump barges or scows and towed to disposal sites several miles away. Discharged dredged material settles through the water column and deposits on the bottom at the disposal site. The dredged material may remain in a mound at the site or disperse depending on the material's physical properties and the hydrodynamics of the disposal site. Open water placement is used with approximately 32% of Great Lakes dredged material (1993-1996). Most open water disposal sites in the Great Lakes are dispersive in nature.
Beach/littoral nourishment involves the placement of dredged material directly onto a beach or into the shallow water. Beach nourishment is typically discharged by pipeline from a hydraulic dredge. Suitable dredged material is typically a fine sand, and may only stay on the beach for a limited time before being eroded into the littoral drift. Littoral nourishment involves a discharge to near shore, shallow areas, and is typically done with bottom dump scows when a mechanical dredge is used. Beach and littoral nourishment are used with approximately 12% of Great Lakes dredged material (1993-1996).
Beneficial use of dredged material includes beach and littoral nourishment (as discussed above) and a variety of upland applications, described here. Upland beneficial uses for dredged material include construction fill, landscaping, agricultural applications and wetland/habitat enhancement. Dredged material from Great Lakes harbors has been used for these and other beneficial uses. For upland uses, dredged material is typically placed into a storage area or CDF for dewatering, and then transported by truck for use. At the Erie Pier CDF in Duluth, dredged material has been "washed" to separate sand for beneficial uses. The development of islands for wildlife habitat with dredged material is typically done by direct placement from a pipeline. The USACE has an authority to provide federal funding (cost-shared) for the additional cost associated with beneficial use of dredged material for the protection, preservation and enhancement of wetlands and aquatic habitat. Additional information on beneficial use of dredged material is available from the Great Lakes Dredging Team, which has conducted a regional workshop on beneficial use and is developing informational materials.
Capping is the placement of a contaminated dredged material in a subaqueous disposal site and covering the material with a layer of clean material. Level bottom capping is the placement of dredged material onto a level bottom surface, forming a mound. Confined aquatic disposal (CAD) involves the use of a depression or excavated subaqueous pit for disposal to provide lateral containment. Cap materials are typically a clean, sandy dredged material. Capping has been used extensively for management of dredged material in the ocean in New York and New England, but has not been used in the Great Lakes.
Confined disposal is the placement of a dredged material into a secure area where the sediment is physically contained. Confined disposal facilities (CDFs) are diked structures that have been built for the disposal of dredged material where in-water placement and beneficial use are not feasible or environmentally unacceptable. The size, shape, design and level of complexity of these facilities has varied widely depending on dredging quantities, methods of disposal, sediment contamination levels, state and local requirements and site characteristics. In addition to CDFs, contaminated dredged material have also been placed in commercial landfills, although this has been done more frequently with environmental cleanup dredging than with navigation dredging. Confined disposal is the most commonly used management practice for contaminated sediments dredged for navigation and environmental remediation. An overview of Great Lakes CDFs is available in Adobe .pdf. The Corps and USEPA are developing a comprehensive report on the status of Great Lakes CDFs, as directed by Congress in Section 513 of the Water Resources Development Act of 1996 (more details will be posted at this site in the future).
Treatment technologies are available to destroy, extract, or immobilize sediment contaminants. A number of treatment technologies were evaluated by the Corps of Engineers as part of a Great Lakes study conducted over 30 years ago. The USEPA Great Lakes National Program Office conducted a comprehensive analysis of sediment treatment technologies under the Assessment and Remediation of Contaminated Sediments (ARCS) Program. Treatment technologies are in varying stages of development, with relatively few available "off-the-shelf" at a full-scale. Because of their costs, state of development, and inability to address the entire suite of contaminants present in many sediments, treatment technologies have been used at only a few of the more than 30 sediment remediation projects around the Great Lakes to date.
There is considerable guidance available on how to evaluate dredged material management options:
- The Great Lakes Dredging Team has developed a white paper on the decision making process for dredged material management specifically focused at Great Lakes Federal and state regulations.
- The USEPA and Corps have developed a Technical Framework for evaluating the management options for dredged material, which addresses the environmental regulations and testing procedures.
- The Great Lakes Dredged Material Testing & Evaluation Manual was developed by the USEPA and Corps for evaluating dredged material proposed for open water placement.
- The Corps of Engineers has developed technical guidance in the form of Engineer Manuals for use in evaluating the feasibility of dredged material management options and in design and construction management.