I respect the commitment of Willamette Riverkeepers, but dredging is not necessarily the most environmentally friendly option. Turbulence caused by dredging can disperse sediment downriver, and in this case the sediment is laced with PCB's and DDT. This is one of the reasons why environmentalists were against deepening the Columbia shipping channel. Even though it may seem irresponsible to leave the pollutants where they are, it could be that capping with a constructed system or natural sedimentation is both the least impactful and cheaper option.