PITTSFIELD, Mass. — More than 30 years have passed since Congress banned a broad range of synthetic compounds called PCBs. Yet 2.65 million cubic yards of mud on the bottom of the Hudson River remain contaminated with the chemicals, which are considered neurotoxins and probable human carcinogens. Since 2002, General Electric has been under federal order to clean approximately 40 miles of the Hudson where its factories discharged PCBs. Preliminary site clearing for the huge project began last week, but actual dredging will not start until 2009 at the earliest. Here, on another PCB-contaminated river about 60 miles to the...