Lower Duwamish Contaminated Sediment Cleanup

Dredging and active placement of Enhanced Natural Recovery (ENR) and ENR+ Activated Carbon (AC) materials to evaluate the effectiveness of ENR+AC compared to ENR alone as a remedial sediment cleanup action in three areas of the LDW in which sediments are contaminated with polychlorinated biphenyls (PCBs). Dredging and placement was performed using a barge-mounted, 1200-6 Hitachi excavator with fixed-arm using a clamshell bucket for submerged placement of the ENR and ENR+AC materials to minimize the loss of AC as the ENR+AC material descends through the water column. The target thickness of the ENR and ENR+AC materials was between 4 and 6-in with an average of 9-in placed over the existing substrate.