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Published in:
2019 | OriginalPaper | Chapter
Dredging Practices and Environmental Considerations
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Excerpt
Beneficial use
Placement or use of dredged material as resource materials in productive ways, which provide environmental, economic, or social benefits.
Confined disposal facility (CDF)
An engineered structure for containment of dredged material consisting of dikes or other structures that enclose a disposal area above any adjacent water surface, isolating the dredged material from adjacent waters during placement. Other terms used for CDFs that appear in the literature include “confined disposal area,” “confined disposal site,” and “dredged material containment area.”
Confined aquatic disposal (CAD)
This is a form of dredged material disposal that involves controlled placement of dredged material into a subaqueous site with some form of lateral confinement. The lateral confinement may be provided by a bottom depression or by subaqueous berms. The contaminated material is then capped in most instances with clean sediment to physically separate it from the overlying environment (commonly called a CAD cell).
Contaminant
A chemical or biological substance in a form that can be incorporated into, onto, or be ingested by or harm aquatic organisms, consumers of aquatic organisms, or users of the aquatic environment. Contaminated sediment or contaminated dredged material.
Contaminated sediments or contaminated dredged materials
Those that may cause an unacceptable adverse effect on human health or the environment.
Dredged material
Material excavated from fresh, estuarine, or ocean waters. The term “dredged material” refers to material, which has been dredged from a water body and disposed in a disposal site. The term “sediment” refers to material on the bed of a water body prior to the dredging process.
Dredging
Underwater excavation is called dredging. “Dredging” is the term given to removal by digging, gathering, or pulling out materials from the bed to deepen waterways and to create harbors, channels, and berths. Dredging is also conducted for construction purposes, for mining, and for environmental cleanup and enhancement.
Habitat
The specific area or environment in which a particular type of plant or animal lives. An organism’s habitat provides all of the basic requirements for the maintenance of life. Typical coastal habitats include beaches, marshes, rocky shores, bottom sediments, mudflats, and the water itself.
Open-water disposal
Placement of dredged material for the purpose of disposal in rivers, lakes, estuaries, or oceans via pipeline or surface release from hopper dredges or barges, without confinement.
Placement of dredged material
In this document, placement of dredged material is considered to be for another purpose other than disposal, such as placement on a beach for beach nourishment or placement on a wetland to enhance the ecological functioning.
Sediment
Material, such as sand, silt, or clay, suspended in or settled on the bottom of a water body. Sediment input to a body of water comes from natural sources, such as erosion of soils and weathering of rock, or as the result of anthropogenic activities, such as forest or agricultural practices, or construction activities. The term “dredged material” refers to material which has been dredged from a water body, while the term “sediment” refers to material in a water body prior to the dredging process.
Suspended solids
Organic or inorganic particles that are suspended in water. The term includes sand, silt, and clay particles as well as other solids, such as biological material, suspended in the water column.
Toxicity
Level of mortality or other end point demonstrated by a group of organisms that have been affected by the properties of a substance, such as contaminated water, sediment, or dredged material.
Toxic pollutant
Pollutants, or combinations of pollutants, including disease-causing agents, that after discharge and upon exposure, ingestion, inhalation, or assimilation into any organism, either directly from the environment or indirectly by ingestion through food chains, will cause death, disease, behavioral abnormalities, cancer, genetic mutations, physiological malfunctions, or physical deformations in such organisms or their offspring.
Turbidity
An optical measure of the amount of material suspended in the water. Increasing the turbidity of the water decreases the amount of light that penetrates the water column. Very high levels of turbidity can be harmful to aquatic life.