After 10 Years of Work, Boston Harbor Tunnel Opens

BOSTON, Massachusetts, September 6, 2000 (ENS) - The water quality in Boston Harbor is expected to improve rapidly after today's opening of the world longest offshore tunnel. The $390 million tunnel will carry all of the treated wastewater discharges from the Deer Island Treatment Plant to a new location nine miles offshore in Massachusetts Bay where deeper water and stronger currents will dilute and disperse Boston's sewage.

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Boston Harbor (Photo courtesy City of Boston)
Massachusetts Water Resources Authority executive director Douglas MacDonald is optimistic. "With the new outfall, there will be a dramatic change. Wastewater discharges to Boston Harbor will end. All the improvements to date around the outfall locations will accelerate as the natural clarity and cleanliness of the water is established. Water conditions should also improve throughout the areas of Massachusetts Bay affected by tidal interchanges of water with Boston Harbor, the Bay's largest estuary."

The new outfall diffuser is 6,600-feet long and is made up of hundreds of individual eight inch discharge ports to assure effective dispersal and dilution of the wastewater stream. It is reached by the 25-foot high tunnel about 100 feet under the surface of Massachusetts Bay.

Discharges will dissipate and disperse rapidly into the surrounding ocean currents. Each gallon of treated wastewater discharged will be mixed almost immediately with more than 100 times that amount of seawater, according to the Massachusetts Water Resources Authority (MWRA).

Construction of the tunnel and its discharge system took more than 10 years and was the single largest project of MWRA's new Deer Island facilities. The construction was performed by a consortium headed by Peter Kiewit Sons of Omaha, Nebraska.

The construction workforce made up of members of the Boston Building Trades Council, including specialized "sandhogs," electricians and operating engineers, worked four million hours to complete the project. A 25-foot diameter tunnel boring machine mined 1.6 million cubic yards of bedrock to excavate the tunnel. The discharge pipes and ports were installed from an adapted oil rig moored over the tunnel's end.

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Deer Island Treatment Plant. Each of the 12, 130 foot tall anaerobic digesters can hold three million gallons. (Photo courtesy MWRA)
Direct discharges of sewage sludge into the Harbor were stopped on Christmas Eve in 1991. Since then, treated sewage has been dumped several hundred feet off the Deer Island treatment plant in Boston Harbor.

"This is a major step in our effort to clean up Boston Harbor and to provide the first class recreational opportunities for our citizens and unpolluted habitat for our wildlife," said Bob Durand, Massachusetts secretary of environmental affairs. "It's important to recognize how this project improves the quality of life for all of us."

But some critics say the money would have been better spent to improve the treatment of wastewater. Others fear the treated sewage, although diluted, will contaminate Massachusetts Bay and Cape Cod.

To answer these concerns, the U.S. Environmental Protection Agency has required extensive scientific monitoring of the outfall effects in MWRA's discharge permit.

Stellwagen Bank, a National Marine Sanctuary, is 16.4 miles from the discharge site. Areas in eastern Cape Cod Bay are feeding grounds of the critically endangered North Atlantic right whale.

MWRA's science program investment of over $20 million has supported teams of researchers from virtually all marine science disciplines. Findings have been pooled and shared in quest of an integrated picture of the harbor and Bay ecosystems.

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Outfall tunnel extends nine miles out into Massachusetts Bay (Photo courtesy MWRA)
Dr. Andrea Rex, a microbiologist who directs marine ecology research and study efforts at MWRA, said, "The science program prompted by the outfall project has created unique research opportunities and led to important scientific and public policy results. Massachusetts Bay and Boston Harbor have become one of the best-studied and best-understood marine environments in the world. Fish veterinarians, plankton biologists, physical oceanographers and benthic ecologists, just to name a few, have shared their insights not only for the benefit of basic science, but to assure that critical environmental policy questions have been soundly addressed."

"Not only MWRA's customers and ratepayers, but U.S. EPA and the National Marine Fisheries Service, have benefited from these efforts," she said.

Ongoing patterns in deep water species are being tracked by ecologists. They note changes from pollution tolerant organisms which appear to be in the process of being replaced by more diverse, healthy communities. Mussels placed near the old harbor outfalls are accumulating lower levels of organic pollutants.

Some investigators predict that seagrass beds may return to wide areas of the once polluted harbor, providing more natural complexity to the ecosystem.

Sampling studies of lobsters showed that while the nearshore environment was important habitat for juvenile lobsters, the offshore location was not, alleviating fears of significant adverse impacts on lobsters from the sewage outfall nine miles from shore.

Dr. Rex sees the future challenge as one of refining the understanding of human and natural effects on this complicated marine ecosystem and to relate them to future policy making so that long term protection of the marine environment can be assured.