METALS - Marine Pollution: What Everyone Needs to Know - page 95

US Environmental Protection Agency. Superfund is the fed-
eral law that identifies the most highly contaminated sites in
the country and eventually impels their cleanup. Technologies
for remediating contaminated sediments are at various stages
of development. Removing the contaminated sediments
by dredging and subsequently putting them in a contained
facility is the most common technique used. Volume reduc-
tion (i.e., removing only the sediments that require treatment
and retaining as little water as possible) reduces costs; preci-
sion dredging techniques can reduce the volume of sediments
that need remediation and thus reduce costs. Treatment costs
may also be reduced through pretreatment. When sediments
must be moved off-site for treatment or confinement, efficient
hydraulic and mechanical methods are available for removal
and transportation. Most dredging technologies can be used
successfully to remove contaminated sediments.
What is natural attenuation?
Natural recovery (doing nothing and letting nature repair itself)
is of low cost and, in some situations, may have the lowest risk
of human and ecosystem exposure to contaminated sediments.
It is most likely to be effective where surface sediment contami-
nant levels are relatively low and are being naturally covered
over rapidly by cleaner sediments, or where natural processes
destroy or modify the contaminants, so that contaminant
releases to the water decrease over time. A disadvantage, how-
ever, is that the more contaminated sediments remain under-
neath, and could potentially be exposed if the overlying cleaner
sediments are resuspended—for example, by severe storms.
What is capping?
Capping involves covering the contaminated sediments with
a deep layer (typically one meter thick) of clean sediments,
which forms the cap. Capping isolates the contaminated