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