Massachusetts Water Resources Authority


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September 5, 2000

MWRA's New Offshore Outfall Promises Environmental Gains for Boston Harbor

MWRA's new Deer Island Treatment Plant has been making improvements to Boston Harbor for over a decade, since direct discharges of sewage sludge into the Harbor were stopped on Christmas Eve in 1991. September 6, 2000 is the latest major milestone: commissioning of the outfall that will carry all of the treated wastewater discharges from the Deer Plant Plant away from small outfalls in the harbor near Deer Island's shores to a new nine-mile distant offshore location, in deeper water with stronger currents, in Massachusetts Bay..

According to MWRA Executive Director Douglas B. MacDonald, "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.

"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, Secretary of Environmental Affairs. "It's important to recognize how this project improves the quality of life for all of us."

The new outfall, reached by a tunnel as large in diameter as the Callahan Tunnel, consists of hundreds of eight-inch ports along a 6,600 foot alignment at a depth of 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 one hundred times that amount of seawater.

Construction of the tunnel and its discharge system took more than ten 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, devoted 4 million hours to 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.

Year by year, recovery of Boston Harbor, celebrated by harbor neighbors, boaters, swimmers, tourists and real estate developers, has moved forward in tandem with the sewage treatment improvements. Other key milestones dates included 1995 when the daily sewage flows from the "north system" communities first passed through new treatment facilities at Deer Island, 1997 when improved facilities for "secondary treatment" by bacteriological action went into service, and 1998 when the discharge to the harbor of "South system" flows from Quincy's Nut Island Plant.

Scientists monitoring the harbor since 1992 have already documented cleaner water and a healthier ecosystems in Boston Harbor from MWRA's improvements. Dramatic improvements should continue. As soon as the new outfall is turned on, the effluent plume now visible on the water surface near the obsolete Deer Island outfalls will disappear. Noticeable increases in water clarity should be seen within hours. Within days to a few weeks, more distant improvements in water quality will begin to be measurable.

Meanwhile, the new discharge into Massachusetts Bay is subject to a permit recently-issued by EPA, after years of citizen input, which subjects the new outfall to some of the most restrictive conditions ever imposed on a metropolitan area's sewage discharges. Millions of dollars of scientific research and monitoring laid the groundwork for the permit and support and on-going program to ensure the recovery of the harbor and the protection of Massachusetts Bay.