DEFINITIONS
The following definitions will aid in understanding the various ways activated carbon can be incorporated into an in-water remedial alternative.
In Situ Capping (ISC) is defined as the placement of an engineered subaqueous cover, or cap, of clean isolating material over an in situ deposit of contaminated sediment. Capping of subaqueous contaminated sediments is an accepted engineering option for managing dredged materials and for in situ remediation of contaminated sediments (EPA 1994, 2002; NRC 1997, 2001; Palermo et al. 1998a and b). ISCs are engineered isolation layers, that historically have been upwards of 2 ft or more addition of clean sediment.
Active or Reactive Capping deploys engineered isolation caps that include amendments to provide additional sorption capacity and retardation of contaminant migration or, possibly, to encourage contaminant degradation. These cap amendments actively control sediment contaminants, compared to the passive action of a conventional sand cap. Thus, caps including these amendments are referred to as active caps or—when transformation is encouraged—reactive caps.
Thin Layer/Residual Capping is placement of a thin cap layer to cover a residual sediment layer left behind following dredging of in situ sediment. While a residual sediment layer may be only a few centimeters thick, residual caps often are 6–12 inches thick and typically are composed of clean dredged sediments or quarry-run sand or soils, and can include active carbon to sequester any residual HOCs..
Enhanced Monitored Natural Recovery (EMNR) is also a placement of a thin cap layer over contaminated sediments, without having first been dredged. The objective is to enhance the natural recovery processes that are occurring at the site. Activated carbon can be included as part of an EMNR remedy. As the acronym implies, monitoring of the natural recovery process to meet the site remedial goals is required.
In Situ Sediment Amendment treats contaminated sediment directly with a material intended to reduce contaminant availability. An amendment, such as activated carbon, is applied directly to the sediment without any additional cover or filler materials. Natural processes, such as re-working of the applied carbon into the sediment by the resident benthic infauna, are relied upon to mix the carbon into the sediment.
Grade Restoration is not a form of capping, although it may be coupled with a designed isolation cap. Often it is a post-dredging requirement imposed by resource agencies to ensure that valuable wildlife habitat can be restored to a clean, pre-removal elevation. In cases where the depth of contaminant removal is greater than the cap thickness required to isolate and contain the sediments, it is possible to achieve some cost savings by arguing for partial sediment removal and a cap to grade
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