Sediment trend analysis of the hylebos waterway: Implications for liability allocations

Abstract

Sediment trend analysis (STA) is a technique that determines the net patterns of sediment movement and their dynamic behavior or stability. The data required are the complete particle size distributions obtained from bottom grab samples collected in a regular grid over the area of interest. Appendix 1 provides the particular details of how STA is undertaken. Because many contaminants are known to associate with the natural particles contained in sedimentary deposits, STA can provide additional weight-of-evidence in ecological risk assessment, remedial investigation, remediation itself, and litigation issues. The STA was applied to 242 sediment samples collected from the Hylebos Waterway, Tacoma, Washington, USA, in support of remedial action planning, contaminant source identification, and ultimately allocation of legal liability for contamination. The Waterway itself comprises a narrow shipping channel extending 3 miles from Commencement Bay (Puget Sound) where it ends in a dredged turning basin (Upper Turning Basin). A 2nd dredged turning basin (Lower Turning Basin) is located about three-quarters of the distance down its length. Both sides of the channel are home to an extensive industrial complex associated with significant contaminant releases into the water. The area was declared a Superfund Site in the early 1980s.The results of the STA showed a consistent pattern of sediment transport directed from the mouth of the Waterway to the turning basin at its head. Divided into 5 separate transport environments (TEs), the sediments within the Waterway progress from transport in Dynamic Equilibrium near the mouth, to Total Deposition (type 1) in the vicinity of the Lower Turning Basin, followed by Total Deposition (type 2) in the Upper Turning Basin. Assuming that contaminants associate preferentially with the finer, rather than the coarser, components of the grain size distributions, a probable behavior of contaminants that can be contained in the sediments is proposed for each TE. Maps showing the spatial distributions of existing contaminant data appear to conform very well to the patterns that might be expected from the STA results. This evidence was primarily used to demonstrate that potentially responsible parties (PRPs) located at the head of the Waterway could not be responsible for contaminated sediments toward its mouth. The findings, for example, effectively dismissed the assumption by the Natural Resource Damage Trustee agencies that contaminated sediments from a particular source would be as likely to migrate down the Waterway as up the Waterway. As a result, major documented sources of contamination near the mouth should be expected to bear a larger share of the total cleanup compared with sources farther toward the head. Furthermore, the STA provided explanations for apparent anomalies such as how hot spots of polychlorinated biphenyls (PCBs) could be located near a property where PCBs had never been released into the environment. If sediment gradient pattern analysis alone were used to all...

The use of grain size trend analysis in macrotidal areas with breakwaters: Implications of settling velocity and spatial sampling density

“…Sampling depth is another important factor that influences the time-scale that the derived trends represent (2001). McLaren and Beveridge (2006) support that the sediment sampling depth has no significance in the determination of sediment transport trends and hence no temporal fluctuations can be identified. On the other hand Gao and Collins (2001) and LeRoux and Rojas (2007) state that the sampling depth has to be in accordance with the physical processes scale.…”

“…The use of bi-or multimodal sediment samples is a point of controversy regarding the determination of the correct grain size trends because of their abundance in the natural environment. McLaren and Beveridge (2006) argued that the use of multimodal sediment samples is not introducing any error in the resultant trends; on the other hand, Gao and Collins (1994a), LeRoux and Rojas, (2007) suggest that the use of such sediments is introducing errors in the determination of the transport direction. A detailed analysis on the impact of bimodal sediment on grain size trends (Flemming, 2007) showed that the use of such sediment samples produce results which are unrelated to the transport processes and sample decomposition into individual populations must be undertaken to such distributions.…”

“…All the above requirements were fulfilled in the present study, whilst conclusions are drawn (see below) considering the limitations of the method. A discussion related to the practical considerations can be found in numerous up-to-date reviews of the grain size trend analysis (Gao and Collins, 2001;McLaren and Beveridge, 2006;LeRoux and Rojas, 2007;McLaren et al, 2007;Poizot et al, 2008).…”

“…A corollary of the above assumption is that there is a greater probability of coarser grains being deposited, prior to finer grains. Although the above assumption does not highlight the complexity of the transport processes (McLaren and Beveridge, 2006) it is reasonable for determining the net transport pathways in marine and coastal environment (Gao and Collins, 1994a,b).…”

Sediment Transport and Contaminant Behavior in the Buffalo River, New York: Implications for River Management

“…Critical to such decisions is an assessment of the likelihood for recontamination after sediment removal, a requirement that demands (i) an understanding of the physical processes that are likely affecting sediment transport, (ii) how those processes relate to the actual patterns of net sediment transport, and (iii) an identification of existing sources of contaminated sediments and their probable transport behavior. The objective of this paper is to assess and discuss each of these criteria utilizing sediment trend analysis (STA), a method that determines sediment transport pathways and dynamic behavior on the basis of the relative changes of grain-size distributions taken from the river bottom (MCLAREN AND BEVERIDGE, 2006). The results presented are from two STA Figure 1.…”