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Remediation alternatives

Several alternative remediation options exist for contaminated sediment sites beyond intrinsic remediation. These include:

Natural recovery. Institutional controls such as fishing advisories minimize exposure while allowing time for the sediment to recover by natural degradation or containment processes. In some cases, the term enhanced natural recovery has been used to refer to the addition of a thin layer of uncontaminated sediment to speed natural depositional processes.

In-situ capping. Placement of a confining layer of uncontaminated sediment on top of the site to mitigate the migration of the contaminants to the biologically active zone. This in-situ containment option may be coupled with active remedial processes with the addition of adsorbents or solidifying agents or through enhancement of biological degradative processes.

Dredging. Sediment removal is followed by:

  • Placement in a confined aquatic disposal site. This entails placing the contaminated sediments in a natural or engineered subaqueous depression and then placing an uncontaminated cap on top.
  • Placement in a confined disposal facility. The dredged contaminated sediment is placed in an above water diked area which is normally adjacent the site. The dredged material will de-water, and often is simply left in this facility.
  • Upland disposal. The contaminated sediments may be disposed in a landfill or treated by sediment washing, solvent extraction, or incineration.

Choosing the best remedial alternative is usually based upon minimizing the risk associated with the contaminants during and after the remediation. Key issues are the ultimate effectiveness of an approach and how long its required to achieve that ultimate effectiveness. Generally, removal options are assumed to be able to achieve the ultimate effectiveness more rapidly but often at the cost of increased short-term exposure and risk. In addition, any removal option leaves a finite residual that ultimately must be managed and is subject to natural recovery.

Natural recovery is generally expected to require a longer period of time to achieve remediation goals but may result in less acute risk during the process. In-situ containment via capping can achieve rapid reduction of exposure and risk but may not be a permanent solution unless natural recovery processes such as biodegradation ultimately reduce the contaminant levels. The open-ended nature of natural recovery and in-situ containment options is often problematic in the face of the dynamic, uncontrolled environment in which many sediments reside. The greater degree of control over the period of exposure and risk during active remedial options often leads to preference for this approach. Natural recovery and in-situ treatment options pose fewer concerns if processes exist for the degradation and loss of contaminants over time rather than simple physical containment. It remains easier to accept a management option that leaves contaminants in-place if containment is not required for an indefinite period.


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