Permanent Solutions For Hazardous Wastes
from Community Ecosystems and Watershed Environments
Contaminated sediment is soil, sand, organic matter, or other minerals that accumulate on the bottom of a water body and contain toxic or hazardous materials at levels that adversely affect human health or the environment.
Contaminants adsorbed to soil or in other forms wash from land, are deposited from air, erode from aquatic banks or beds, or form from the underwater breakdown or build-up of minerals.
Contaminated sediment is present in wetlands, streams, rivers, lakes, reservoirs, harbors, along ocean margins, or in other water bodies. Some contaminants have both man-made sources and natural sources (e.g., many metals and some organic compounds).
Examples of primary and secondary sources of contaminants in sediment are included in
- Direct pipeline or outfall discharges into a water body from industrial facilities, waste water treatment plants, storm water discharges, or combined sewer overflows
- Chemical spills into a water body
- Surface runoff or erosion of soil from floodplains and other contaminated sources on land, such as waste dumps, chemical storage facilities, mines and mine waste piles, and agricultural or urban areas
- Air emissions from power plants, incinerators, pesticide applications, or other sources that may be transferred to a water body through precipitation or direct deposition
- Seepage of contaminated ground water into a water body
- Direct disposal from docked and dry-docked ships, or release of contaminants from in-water structures and over-water structures or ship maintenance facilities
Organic contaminants in sediment typically adsorb to fine sediment particles and exist in the pore water between sediment particles. Metals also adsorb to sediment and bind to sulfides in the sediment. The relative proportion of contaminants between sediment and pore water depends on the type of contaminant and the physical and chemical properties of the sediment and water. Pore water in sediment generally is interconnected with both surface water and ground water, although the degree of interconnection may change from place-to-place and with flow changes in ground water and surface water.
Many contaminants persist for years or decades because the contaminant does not degrade or degrades very slowly in the aquatic environment. Contaminants absorbed to sediment normally develop equilibrium with the dissolved fraction in the pore water and in the overlying surface water to be taken up by fish and other aquatic organisms. Some bottom-dwelling organisms ingest contaminated sediment, and in shallow water environments, humans may also come into direct contact with contaminated sediment. Some contaminants, such as most metals, are hazardous primarily because of direct toxicity.
Although some metals do accumulate in biota (i.e., bioaccumulate), generally they do not significantly increase in concentration as they are passed up the food chain. Concentrations in fish may endanger humans and wildlife that eat fish. Women of childbearing age, young children, people who derive much of their diet from fish and shellfish, and people with impaired immune systems may be especially at risk.
In addition, contaminated sediment can significantly impair the navigational and recreational uses of rivers and harbors.
Navigational dredging is not currently being performed in many harbors and waterways because of the concern for impacts of dredging on water quality, liability to those performing the dredging, and disposal options for the contaminated dredged material.
Contaminated land
Contaminated land has major economic, legal and planning implications for the community.
Contamination may limit land use potential or increase costs for developers and councils. Clean-up is important to protect human health and the environment.
Although contaminated sites can occur anywhere, they are typically clustered in areas which have been used for heavy industry or chemically intensive agriculture.
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