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OCR for page 1
EXECUTT~E SUMMARY
Contamination of marine sediments poses a potential threat to
marine resources and human health (through consumption of seafood) in
numerous sites throughout the country--particularly near metropolitan
areas. Improving the nation's capability to assess, manage, and
remediate these contaminated sediments is critical to the health of the
marine environment as well as to its use for navigation, commerce,
fishing, and recreation. As widespread as the problem of sediment
contamination appears to be, understanding of the geographical extent
and ecological significance of the problem is not well developed. In
addition, management and remediation of contaminated marine sediments
requires grappling with dynamic aquatic environments in which
contaminant mobilization can occur in response to remediation itself,
or as a result of natural resuspension, transport, and deposition of
the bottom sediments.
This report, prepared by the Committee on Contaminated Marine
Sediments of the Marine Board of the National Research Council,
examines the extent and significance of marine sediment contamination
in the United States; reviews the state of the art of contaminated
sediment clean-up and remediation technology; identifies and appraises
alternative sediment management strategies; and identifies research and
development needs and issues for subsequent technical assessment. The
report contains the results of a symposium and workshop, with
supplementary discussion and recommendations by the convertors.
The committee members concluded that sediment contamination is
widespread throughout U.S. coastal waters and potentially far reaching
in its environmental and public health significance. A report
sponsored by the U.S. Environmental Protection Agency (EPA), although
limited in its data sources, estimated that there are "hundreds of
sites in the United States with in-place pollutants at concentration
levels that are of concern to environmental scientists and managers.
More than one-third involve marine or estuarine waterways." The
National Oceanic and Atmospheric Administration's (NOAA) National
Status and Trends Program, which selectively excluded "hot spots" from
its sampling, found high levels of contamination in samples from sites
in major urban areas, including Boston, New York, San Diego, Los
Angeles, San Francisco, and Seattle. However, adequate data do not
currently exist for comprehensively pinpointing or prioritizing
1
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candidates for remedial action. Even so, the means and methods for
making such determinations are available (or close at hand), albeit
needing much improvement. They include several that were evaluated by
the committee.
At present, no single technique is widely accepted and each has its
advantages and disadvantages. A number of approaches may be needed to
evaluate the significance and extent of contamination at any given
site. Ultimately the methods used should be able to be conducted
routinely and cost-effectively.
In terms of risk to human health, transfer of contaminants from
marine sediments to humans is poorly documented and underassessed.
However, it appears that there may be cause for concern with regard to
persistent bioaccumulative chemicals contaminating seafood. The impact
of this type of contamination needs further investigation.
Despite the widespread extent of the contaminated sediment problem,
remedial actions directed at excavating, treating, or otherwise
manipulating contaminated marine sediments have been extremely rare.
Under the Superfund law, only sites designated on the National
Priorities List can be funded for remediation. The Hazard Ranking
System score, which determines placement on this list, gives heavy
weight to potential contamination of drinking water sources, but little
or no weight to sediment-mediated contamination of edible fish and
shellfish. Furthermore, little effort has been made to identify
contaminated sites in coastal environments under Superfund.i
In its examination of state-of-the-art clean-up and remediation
technology, the committee determined that existing technology is
adequate in most situations. However, the committee noted that some
specialized dredging equipment--e."., to allow excavation of
contaminated sediments with a minimum of turbidity--is difficult to
obtain in the United States (due to cabotage laws). To alleviate this
problem, government support is encouraged for efforts to acquire or
develop dredging equipment with features that make it well-suited to
the excavation of contaminated sediments.
The committee also found that the time required for EPA or its
contractors to make a clean-up decision was more often a limiting
factor in accomplishing effective clean-up than any constraints imposed
by limitations in clean-up science or technology. The time required
for a decision was sometimes speeded up, however, where the need for
navigational dredging was a driving force.
Remediating underwater sediment contamination can be a complex
problem. Failure to make a decision may cause the problem to spread.
Although in many instances the problem may correct itself given enough
time, it is usually desirable to isolate and contain the contaminated
area to the extent possible. Allowing the affected area to expand will
generally only serve to increase the cost and complexity of the
eventual clean-up. More attention needs to be focused on the design of
1Although as many as 141 of 1~100 (13 percent) present and proposed
Superfund National Priorities List sites may be located adjacent to
coastal areas and may or may not involve coastal sediments, no remedial
action has been selected for the great majority of these sites.
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rapid short-term actions to limit the spread of contamination at the
same time that more elaborate long-term remedies are assessed and
developed.
In some cases, no action can be the alternative of choice, assuming
measures have been adopted to control contamination sources. This may
be particularly true when natural sedimentation or dispersal may
mitigate the problem or when natural detoxification of contaminants is
occurring. During an evaluation process, the effects due to
remediation should be compared with those associated with the no-action
alternative.
The committee recommended that future research and development be
focused on
establishing better better biological and chemical techniques
for rapidly and reliably assessing the presence and severity of
bottom sediment contamination,
delineating the practical limits of capping as an efficacious
remediation technology,
identifying interim measures to limit the spread of contaminated
sediments while long-term remedies are assessed, and
formulating procedures and guidelines that adequately evaluate
and prioritize health and environmental risks associated with
sediment contamination, and against which effectiveness and
clean-up needs can be measured.
The committee also believed that in view of the high cost of most
remedial actions, greater use should be made of benefit-cost
comparisons. This would place investment in this area on the same
economic footing as investments in other public projects.
Cost-effectiveness analysis of alternative remedial actions, including
"no action," should consider both short- and long-term costs,
comparisons at and among sites, and incremental costs of additional
levels of clean-up of contaminated sediments.
Finally, increased emphasis on sediment assessment and clean-up
practices has caused rapid changes and developments in state-of-the-art
technologies. Developments and experience in methods for applying
these technologies are also occurring at a rapid rate. Therefore, it
is an important and appropriate role for the federal government (either
through individual concerned agencies or, preferably, through a
coordinated interagency committee) to frequently review and evaluate
the effectiveness and scientific basis for newly developed sediment
assessment and clean-up technologies and procedures.
Representative terms from entire chapter:
contaminated sediments
