Dredging and the management of dredged material are an important function of Corps districts. Typically, about 4 million cubic yards of sediments are dredged by the Corps of Engineers each year from Great Lakes harbors and channels, the equivalent to 400,000 truck loads of soil. On average, the Corps of Engineers spends about $20 million dollars annually for dredging and dredged material management in the Great Lakes Basin.
Dredged material is a term used to describe the material excavated from a river, harbor or lake by a dredge. In the case of maintenance dredging, the material is sediment that has accumulated in the channel bottom since the last time it was dredged. In rivers, these sediments are soils that have been eroded from farmlands, forests, and gardens or washed off city street and carried by the water before depositing in a deepened channel. In the harbors and entrance channels that extend out into the lakes, the sediments are sand and silts that have been carried along the lake shoreline by littoral currents and deposited in the deepened channel. Over 90% of the dredged material is a clean soil that is physically and chemically the same as the soil on a field or in the park. The other ten percent may have contaminants that came from a number of possible sources including urban runoff and sewer overflows.
Sediments dredged from Great Lakes harbors and channels may be managed using one of the following methods:
- Open water placement (placement directly in the lake or river)
- Beach nourishment (placement on the beach or in the nearshore area)
- Capping (placement on the bottom of a lake and covering with clean material)
- Upland beneficial use (use for construction fill, landscaping, landfill cover, etc)
- Confined disposal (placement in a CDF or licensed landfill)
- Treatment (applying one or more processes to remove or destroy contaminants.
The selection of the appropriate option for managing a dredged material is based on the type and level of contaminants present (if any), the volume of materials, local conditions, and environmental, social and economic factors. The Corps is required to use the disposal alternative that is least costly and complies with applicable environmental laws and regulations.