New Bedford Harbor Superfund Site

History & Location

The 18,000 acre New Bedford site is an urban tidal estuary with sediments which are highly contaminated with polychlorinated biphenyls (PCBs) and heavy metals.  Manufacturers in the area used PCBs while producing electric devices from 1940 to the late 1970s, when the use of PCBs was banned by the EPA.  These facilities discharged industrial wastes containing PCBs directly into the harbor and indirectly via the city’s sewerage system.  As a result, the harbor is contaminated in varying degrees for at least 6 miles, from the upper Acushnet River into Buzzards Bay.  Bioaccumulation of PCBs within the marine food chain has resulted in closing the area to lobstering and fishing, and recreational activities and harbor development have been limited by the widespread PCB problem.

Significant Project Features

• Hydraulic dredging and mechanical dewatering of PCB contaminated sediments with highest concentrations of 7,650 ppm in a phased multi-year approach. Over 740,650 CY of PCB contaminated sediments have been removed
• Design, installation, operation and maintenance of a liquids/solids separation system and wastewater treatment system to handle a 2,000 GPM flow rate
• Dredge spoils conveyance system required 20,000 lf of dual containment piping
• 300 million gallons of filtrate successfully treated to meet criteria limits establish for metals and PCB’s (parts per trillion)
• Mechanical dredging of 100,000 CY of PCB contaminated sediments for disposal in subaqueous CAD cell
• Water depths ranging from 3-30 feet
• Tidal ranges of 3-6 feet
• Bottom dump scows used to transfer and place dredged sediments
• Use of Sevenson owned equipment including PC450, PC800, Sennebogen 850, 100 CY scows, 2.5 CY and 5.5 CY environmental buckets and support equipment
• Use of single beam surface bathymetry
• Water Quality (WQ) Management
• Large, non-homogenous dredging footprint

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