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(W/EH078) Assessment of Sediment Transport in Remediation of a Contaminated Estuarine Bay. Pascoe, Gary1, McLaren, Patrick2, 1 2 ABSTRACT- Sediment toxicity of a small bay located on Dyes Inlet of Puget Sound, Washington, USA, exceeds regulatory agency sediment quality criteria based on toxicity. An assessment of sediment transport and deposition in the bay was performed to determine whether contaminated sediment from outside the bay may contribute to observed toxicity. A Sediment Trend Analysis (STA®) was performed on grain size data from 400 surficial grab samples throughout the bay and inlet. The STA identified net sediment transport pathways by examining changes in grain size distributions in multiple adjacent samples. Results of the STA and sedimentology using lead-210 indicated that fine-grained sedimentary material transports into Dyes Inlet from western Puget Sound and deposits throughout the inlet and the bay. Echinoderm larval bioassay results using fine-grained sediments were similar for the bay and Dyes Inlet, and all stations of both water bodies exceeded toxicity-based sediment quality criteria. Mercury concentrations in the bay and the inlet ranged from 0.48 to 1.4 mg/kg, with no differences in average concentrations between the water bodies. Results of the STA, bioassays, and sediment chemistry suggest that impacted sediment in the bay is partly the result of unknown sources of impacted sedimentary material transporting into and depositing throughout the Dyes Inlet system. Continued deposition of impacted material will prevent natural recovery of the bay and the inlet. Modeling indicates that the continued deposition will also result in failure of sediment covers to meet regulatory criteria within 10 to 40 years. Stakeholders have agreed that remediation of the bottom sediment of the bay can be implemented only after the toxicity of depositing sediment is shown to decrease. Key words: sediment transport, sediment remediation, sediment trend analysis, estuarine |
