Massachusetts Targets PCB “Hot Spot” for Dredging

Source: Engineering News Record
Environmental officials in Massachusetts spent $14 million to dredge and incinerate a “hot spot” of polychlorinated biphenyls (PCB’s) at the bottom of New Bedford harbor. The cleanup purged sediments in a 5-acre area of the Acushnet River estuary where about 45% of the harbor’s chemicals and heavy metal pollutants are concentrated.

The 1000-acre harbor has the nation’s highest concentration of PCB’s and is one of the worst sites on the Superfund National Priorities List. Dredging the “hot spot” is intended to curb migration of contaminants into the rest of the harbor.

The cleanup’s first phase, designed by the Corps of Engineers, involved excavating about 10,000 cu.yd. of the estuary bottom to a maximum depth of 4-ft using an Ellicott® Series 370 cutterhead dredge operated by AGM Marine Contractors that will minimize the diffusion of sediments. The dredged material will be pumped through a 3,000-ft floating pipeline to a confined disposal facility at the water’s edge in New Bedford.

The material will be dewatered, and effluent from dewatering will be treated to remove PCBs and heavy metals prior to discharge into the harbor. The dewatered sediment will then be incinerated, destroying the PCBs. Incineration ash containing the metals will be solidified, buried and capped on the site temporarily. “Its final disposal will depend on how the rest of the harbor is cleaned,” said Mark Otis, a civil engineer in the Corp’s New England division office in Waltham.

The plan for “hot spot” dredging and land disposal follows a pilot study that included placing contaminated sediment in a deep hole in the bottom of the harbor and capping it with clean material. “We did not succeed in getting a real clean cap,” said Otis. However, the method might be tied to the second phase of the harbor cleanup, said a U.S. Environmental Protection Agency spokeswoman.

The Corps began the first phase of the cleanup the end of 1991.
Reprinted from Engineering News Record