PCB Dredging Cleanup Project Begins On Lake Cochituate (USA)

A large ring of yellow buoys floats beside an an Ellicott 300 SL 8″ Swinging Dragon™ dredge on the surface of Pegan Cove, marking the area where contractors have started removing sediment contaminated with PCBs, left by an accident at the Soldier Systems Center 30 years ago.

The PCBs were found in the section of Lake Cochituate just to the east of Natick Labs. They came from a transformer explosion in 1980 and got into the lake through a storm drain, said Jim Connolly, restoration program manager for Natick Labs.

Charter Environmental of Boston is handling the cleanup, with dredging work done by subcontractor Inner Space Dredging of Maine using an an Ellicott 300 SL 8″ Swinging Dragon™ dredge. The Defense Department is picking up the $2.8 million tab, Connolly said.

“It doesn’t come out of the (Natick Labs) budget,” Connolly said.

Connolly said work will run through Sept. 7.

The barrier of buoys holds up silt screens, which will prevent any sediment kicked up during dredging from spreading. A dredge creeps along the surface, and sucks up the sediment and some water, which flows through a pipe at a rate of up to 1,500 gallons per minute. The sludge is collected in geotextile bags that can grow to as big as 6 feet high, and are a few hundred feet long.

Then a flocculant, a substance that makes the silt separate from the water, is put into the mixture inside the bags. The excess water then seeps out of the bag through small holes that do not allow the sediment to escape.

After the silt is dried, it will be taken to an off-site landfill that deals with PCBs and other contaminants, Connolly said.

The water that comes out of the bags will eventually be returned to the lake.

“We will test the water to make sure it is clean,” Connolly said.

Three sections of the lake will be dredged, Connolly said. Several hundred samples have been taken over the years, he said, and the areas just off the shore of Natick Labs will be dredged.

“We are only taking the top six inches of sediment,” Connolly said. “The exception of that is at the (storm drain) outfall, where it will go deeper.”

Marco Kaltofen, a Natick resident and member of the Restoration Advisory Board for the cleanup, said he is glad the project is finally under way.

“It’s not perfect, but it’s a good, large step foward,” Kaltofen said. “It’s been on my radar and on the board’s radar for 10-plus years.”

Much of the holdup has been due to the red tape that goes along with a Superfund project, Kaltofen said. He had worried that the money would not be available.

The cleanup was triggered when authorities found unsafe levels of PCBs in fish caught in Lake Cochituate. Kaltofen, an environmental engineer, said the fish are his biggest concern.

“The fish from Lake Cochituate are really nasty,” Kaltofen said. “I have been to toxic sites all over the country and very few have anywhere near the level of PCBs as the ones at Lake Cochituate.”

While there are signs warning people not to eat the fish, and mailings have gone out to nearby homeowners, some still catch and eat fish from the lake.

“Every day in the summer time I see people fishing and taking stuff home,” Kaltofen said. “A lot of people may not be as well connected, or be from the community. They may not be getting mailings from the (Natick Labs).”

The cleanup will lead to lower levels of PCBs, Connolly said, because the fish will not be eating as much PCB-contaminated food from the bottom of the lake.

Kaltofen said it may take several years for the PCBs to drop to safe levels.

“The Superfund program has a five-year review program where they go back to see if levels have dropped,” Kaltofen said. “I don’t know how many five-year periods it will take, but I expect it will be more than one.”


Source: Ellicott Dredges