At bottom, Charles is still polluted

By Beth Daley
March 30, 2001

Although the water in the Charles River is the cleanest it has been in two centuries, the sediment on the bottom is five times more contaminated than in many of the nation's other urban rivers, according to a report being released today.

The finding raises new doubts about the progress of a federal and state plan to make the river clean enough for fishing and swimming by 2005. Removing toxins from the sediment is the hardest part of the decade-old effort to clean up one of the nation's filthiest rivers.

''We expected to face some serious problems,'' said Bob Zimmerman, executive director of the Charles River Watershed Association, a river advocacy group. ''Getting the river from [an environmental grade of] D- to a B is a lot easier than getting it from a B to an A. And that's the tough part we are embarking on now.''

Layers of contaminated sediment in the Charles - five feet deep by the Museum of Science - are a capsule history of industrial Boston. Tanning factories, slaughterhouses, paint manufacturers, and many other industries dumped myriad pollutants into the river, which then settled on the bottom.

While the sediment doesn't visibly affect water quality, it can contaminate the water if it is stirred up. Swimmers at planned bathing beaches such as Magazine Beach in Cambridge or the Esplanade lagoon may not want to go wading until the contaminated sediment is gone, scientists say. Other planned beaches, such as Herter Park and Daly Field in Brighton, have high levels of contaminants. Those beaches may have to be relocated, officials said.

''You still might be reluctant to swim and kick up the sediment or fish because the fish might be accumulating contaminants through the food chain,'' said Kenneth Finkelstein, an environmental scientist with the National Oceanic and Atmospheric Administration. Still, he said, there have been few studies showing exactly how toxic the sediment is to aquatic life.

Contaminated sediment is only one of the river's problems. Saltwater from the ocean also does damage, according to reports by the US Geological Survey. Every time the Charles River Dam by the Museum of Science opens to let boats from Boston Harbor in, hundreds of thousands of gallons of saltwater also enter.

The cooler, heavier saltwater sinks below the lighter, warmer freshwater. The layering doesn't allow the water to mix, so freshwater oxygen from the surface can't reach the fish below. The result can be fish die-offs.

That condition also causes a chemical reaction that binds the sediment contaminants in place. ''It really adds to the problem,'' said Robert Breault, a hydrologist from the Geological Survey.

Exactly how to solve the problems is unclear. The salt problem could be eased with a device that mixes the salt and fresh water. But the whole river can't be dredged to get pollutants out of the sediment - that would be far too expensive and technologically challenging. The Environmental Protection Agency will consider spot-dredging, taking dirty sediment out of areas people are likely to use and replace it with clean fill. In addition, officials may be able to cap the contaminated riverbed by covering it with clean dirt.

Zimmerman has an even more novel idea: Mining heavy metals such as cadmium out of the riverbed to help pay for the dredging. Such mining has been done at some hazardous waste sites.

''This is the worst sediment problem in an urban river,'' Zimmerman said. ''We don't know if we can mine, but we should look at it. We need to be creative.''

While officials struggle over how to clean the old sediment, they will also be looking at contaminants that still wash into the river from roads and riverbanks.

''We didn't expect to be diving into the river right away,'' said Chuck Borstel, spokesman for the Metropolitan District Commission, which oversees the Charles. ''We know we still have a long road, but we are fully committed to the 2005 goal.''