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.