Sediment
Capping
Description
In sediment capping submerged contaminated sediments are covered by
stable
layers of sediment, gravel, rock, and/or synthetic materials. In
certain
conditions, the cap reduces contaminant
mobility and subsequent interaction between aquatic organisms and the
contaminants. Even where contaminated sediments must be excavated,
underwater
capping may still be preferable to above ground disposal. In this case,
sediments may be deposited in either a natural depression or a space
formed by
dredging clean sediment before capping.
Capping is only appropriate if the following circumstances apply:
Limitations
and Concerns
With capping, contaminants remain in place at the site, requiring
long-term monitoring
and maintenance to ensure that contaminants are not migrating. The
integrity of
the cap should be investigated regularly. The cap should be designed to
provide
containment for as long as the contaminated sediment requires
management.
Moving contaminated sediment (if required) and placing the first
layer of
capping material can suspend sediment in the water column.
Strong currents can displace capping materials.
Capping materials reduce the available clearance for water traffic.
Thus, at
times the use of the waterway may dictate that contaminated sediments
be moved
from their original site.
The tendency for sediments to flow because of the momentum generated
during
cap placement should be carefully analyzed to prevent sediment
entrainment and
contaminant release.
Applicability
This technology is best used to contain volatile
organic
compounds (VOCs),
semi-volatile
organic
compounds (SVOCs) [including polychlorinated
biphenyls (PCBs) and polynuclear
aromatic hydrocarbons (PAHs)], pesticides,
energetics, and metals. It is used in ocean shoreline situations. It is
being
studied for
some river applications.
Technology
Development Status
This is a commercial technology.
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