Newark Bay Study - Passaic River Public Digital Library

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flow rates, in combination with the associated suspended solids load, lead to the advection of both
dissolved and sorbed chemicals along with the water. The effect may differ from one location to
another. For example, the analysis performed by Suszkowski indicates that, in the case of the
Passaic River, there is a net movement (i.e., the difference between upstream and downstream
transport) of suspended solids in the downstream direction towards Newark Bay. (Note that it does
not necessarily follow that the net movement of chemicals will be in the same direction as the net
movement of solids, as the dissolved and sorbed chemical concentrations in the surface and bottom
layers also need to be considered.) Should this finding be confirmed by future data and modeling
analyses, it can be expected to have important implications to the evaluation of the rates of chemical
exchange between the Passaic River and Newark Bay. In contrast to the Passaic River there is a net
flux of solids from Newark Bay into the Hackensack River (Suszkowski, 1978; Pence, 2004). This
finding also has important implications to the net movement of chemicals between these two
regions and should be confirmed in subsequent analyses.
Another important aspect of solids transport in Newark Bay that was quantified by
Suszkowski was the high rates of sediment accumulation in a number of localized areas, including
Port Newark and in the channel north of Shooters Island. He attributed the deposition of solids in
these regions to factors that were largely site-specific in nature. It will be important for the model to
properly simulate the accumulation of solids in these localized areas, in part because these are areas
where maintenance dredging takes place. While not a natural process, maintenance dredging will
serve as a sink of both solids and chemicals in Newark Bay, as it leads to removal of mass from the
system. It is expected that a relatively high-resolution model grid will be required to properly
simulate the observed high rates of deposition in these localized areas. Use of a high-resolution grid
will improve the level of detail that can be represented by both the hydrodynamic and sediment
transport models, and as such, should enhance their predictive abilities. This is important since the
chemical fate model will use these results to quantify the associated chemical transfers. The
significance of removal of dredged material as a sink of chemicals in these areas remains to be
evaluated.
Sediment transport also has an important bearing on chemical fate via the manner in which
the process of burial is represented (Berner, 1980; Boudreau, 1997; Boudreau and Jorgensen, 2001).
Sediments typically have a surficial layer where particle mixing occurs as a result of reworking by
benthic organisms (bioturbation) and by physical mixing processes related to settling and
resuspension. A number of approaches may be used to evaluate the depth over which mixing
occurs, including but not necessarily limited to biological surveys of the benthic community,
sediment profile imaging, and consideration of radionuclide data. Mixing alone results in the
transfer of chemicals along a concentration gradient, from areas of high to low concentration. It is
for this reason that historically contaminated sediments, even if buried by the accumulation of clean
solids long after the chemical source has been eliminated, may continue to exhibit residual