Duwamish contaminant in suspended sediments

Thomas Gries

We collected samples upstream of the southern boundary of the lower Duwamish clean up area and then compared with samples taken further downstream.   Background: focus on Harbor Island and a cleanup site at river mile 4.8, site selection and future load inluenced by sediment transport model and analysis report:

  • >95% sediment load from upstream
  • 50% fine suspended sediment passes through site

Upstream sampling at 6/1oth max depth was chosen to avoid upstream transport by salt wedge, but downstream of most point-sources.  Looked at 63 and 250 micon sediment size fractions. We saw high [PCB, dioxins, arsenic] in August, low in November and December.  Suspended sediment PCB loading may be lower than predicted.  Peak loading is associated with storm events.

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