Contaminated Sediments in Ports and Waterways Cleanup Strategies and Technologies (1997) / Chapter Skim
Currently Skimming:
4 Site-Specific Considerations
4 Site-Specific Considerations
Pages 62-79
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From page 62... ...
This chapter deals with contaminant sources, transport processes, and methods of site characterization. Site-specific considerations are important, in the committee's judgment, because inadequate source control and site assessment can undermine the best management practices.
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From page 63... ...
Thus, contamination may persist, leading to a continuing need to dredge and redredge contaminated sediments, which is costly and politically unacceptable. Source control could be encouraged in navigation dredging projects through regulation, as long as the question of who pays is resolved in a manner that is acceptable to all parties.
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From page 64... ...
In situations where watershed planning has failed and identifiable upstream sources have contributed disproportionately to sediment contamination downstream, the EPA could be authorized to recover an appropriate share of cleanup or disposal costs from the responsible parties. Part of the EPA's draft document on a strategy for managing contaminated sediments (EPA, 1994)
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From page 65... ...
In the water column, the sizes of these aggregates and their associated settling velocities are controlled by the balance between collision and breakup forces induced by flow-associated shear. This force balance continuously changes as the particles migrate through differing flow regimes caused by horizontal advection and turbulent mixing.
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From page 66... ...
The latter process can be particularly pronounced in sulfate-rich seawater, resulting in the precipitation of trace metals by sulfides in the anaerobic pore waters and the subsequent down-gradient diffusion from surficial, aerobic sediments to the deeper anoxic pore waters. The rates of degradation of organic matter are also affected by the shift from oxidizing to reducing conditions within the upper levels of the sediment column (the redox gradient)
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From page 67... ...
The knowledge of present contaminant discharges and local transport dynamics can provide an immediate indication of the long-term effectiveness of a contaminant removal strategy and the overall advisability of proposed uses of the site. Source control is an important element in the management of contaminated sediments.
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From page 68... ...
68 CONTAMINATED SEDIMENTS IN PORTS AND WATERWAYS FIGURE 4-1 Conceptual site assessment protocol. search of a variety of repositories, including state and federal permit files and water quality data; municipal planning, zoning, and land-use records; and assessors' files of deeds and titles dating back to the preindustrial period.
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From page 69... ...
This information is essential to the design of subsequent field surveys and, if carefully gathered, can increase significantly the cost effectiveness of field surveys. The experience of committee members suggests that the value of historical reviews for enhancing cost effectiveness is often overlooked.
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From page 70... ...
Depending on the location, it may be possible to define the majority of these factors using existing information. Data are needed concerning the topography of adjoining lands and ground cover characteristics; local tidal height and currents; stream flows; meteorology, particularly wind speed and direction and concurrent air temperatures; water depths; and surficial sediment characteristics.
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From page 71... ...
The remaining factors detailing the regional flow regime permit evaluation of the sensitivity of the transport system to changes in meteorological and hydrological conditions, particularly aperiodic storms. Initial site evaluation, in combination with data detailing sediment contamination, enables decisions to be made concerning the need for and form of supplemental field surveys.
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From page 72... ...
The procedure is not intended to yield high-resolution spatial data detailing contaminant concentrations throughout an area. Efforts to obtain such data would be initiated only if justified by the results of the initial field survey(s)
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From page 73... ...
. Although physical coring is the most common and reliable method for detailed mapping of contaminant distributions, it is a slow and expensive process and, depending on the heterogeneity of the sediment column and the number of potential contaminant sources, it tends to provide limited spatial resolution.
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From page 74... ...
Committee members had different views regarding the potential of acoustic profiling for differentiating between contaminated and uncontaminated sediments. Initial research results suggest that the use of acoustic profiling in site assessment, combined with precision dredging, has the potential to reduce the costs of contaminated site remediation.
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From page 75... ...
The availability of such sensors would contribute significantly to the development of improved management protocols for contaminated sediment sites. Survey Design: Numerical Simulation Methods Designs of sediment sampling strategies, and identification of optimum remediation methods, increasingly rely on computer-based numerical models.
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From page 76... ...
In turn, exposure data typically serve as essential input for numerical models of species toxicity and subsequent ecosystem response. The lack of accurate data, combined with the limited understanding of the effects of an assemblage of contaminants acting individually and synergistically on selected species, significantly limits the accuracy of numerical models of toxic response.
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From page 77... ...
For example, the EPA and the states could consider the impact on sediment quality downstream in setting TMDLs for waterway segments and in developing load allocations for contaminant sources. Site assessment represents an essential element in the design and implementation of every contaminated sediment management plan.
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From page 78... ...
1991. Rapid, subsurface, in-situ field screening of petroleum hydrocarbon contamination using laser induced fluorescence over optical fibers.
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From page 79... ...
1987. Principles of Surface Water Quality Modeling and Control.
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