Boston Harbor and Massachusetts Bay
MWRA Environmental Quality Department

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The Boston Harbor Project

In 1985, under a federal court order, MWRA was created to plan and construct new sewage treatment facilities to end the discharge of untreated and partially treated sewage to Boston Harbor. The “Boston Harbor Project,” as it was called, included four major construction projects:

1. Pelletizer Plant: Facilities at the Fore River shipyard in Quincy to process sewage sludge into commercial fertilizer pellets, ending the discharge of sludge into the harbor.

2. A new secondary wastewater treatment facility, the new Deer Island Treatment Plant (DITP), to replace the failing and undersized primary treatment plants at Deer Island and Nut Island (NITP).

3. A tunnel from Nut Island to DITP to transport South System sewage to DITP for secondary treatment, enabling flows from throughout MWRA’s service area to receive secondary treatment and greatly lessening pollution to the harbor.

4. An outfall in Massachusetts Bay to discharge treated effluent 9.5 miles offshore into Massachusetts Bay, increasing dilution and minimizing potential environmental impacts in the bay.

Combined Sewer Overflow (CSO)

In addition to taking on these major construction projects, MWRA started addressing the problem of combined sewer overflows (CSOs), which discharge a mixture of stormwater runoff and sewage directly into the harbor during heavy rainstorms. In the 1980s, 88 CSOs in the harbor and its tributary rivers discharged an estimated 3.3 billion gallons of partially treated or raw combined sewage annually.