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Boston Harbor Outfall Tunnel

Boston, Massachusetts, United States

Client: Massachusetts Water Resources Authority

Parsons Brinckerhoff Role: Design

Boston Harbor Outfall Tunnel
The Boston Harbor Effluent Outfall Tunnel was a key part of the Boston Harbor Project, a $4 billion effort to clean up Boston Harbor by providing new wastewater infrastructure including a new sewage treatment plant at Deer Island in Boston Harbor and an associated 9.5-mile (15.2-kilometer) outfall tunnel.

Parsons Brinckerhoff, as a subconsultant, designed the 25-foot-diameter (7.6-meter) tunnel on behalf of the Massachusetts Water Resources Authority (MWRA). One of the longest and largest outfalls in the world, the tunnel was a key part of the MWRA’s Boston Harbor Project, a court-ordered program to improve the water quality of Boston Harbor, making it swimmable and fishable. As part of its services, Parsons Brinckerhoff provided extensive geotechnical exploration and geophysical exploration prior to construction of the tunnel.

The outfall includes a 400-foot-deep (121-meter) onshore shaft at Deer Island and 55 riser shafts that connect the final section of the tunnel to diffuser caps in the deep waters of Massachusetts Bay.

In September 2000, the outfall began discharging twice-treated wastewater nine miles (15 kilometers) into Massachusetts Bay. “This is a major step in our effort to clean up Boston Harbor and to provide first-class recreational opportunities for our citizens and unpolluted habitat for our wildlife,” said the Massachusetts Secretary of Environmental Affairs.

Parsons Brinckerhoff offers engineering solutions to cities around the world eager to clean up their waterways and secure the water supply needed for prosperity and growth. We design and manage construction of water-supply tunnels, combined sewer overflows (CSOs), tunnels and offshore outfalls, and deep shafts in all ground conditions. Our particular strengths include ground improvement to protect surrounding structures, tunneling in gassy or contaminated ground, and seismic engineering that keeps water tunnels operable in the event of earthquake or other disasters.

Water conveyance system design and construction must answer a community’s demand for safe drinking and agricultural water, environmentally sound wastewater handling, and economical stormwater management.  Our experience includes the planning, design, and construction management of pipelines, sewers, outfalls, force mains, separate and combined collection systems, pump stations, flow control facilities, canals and dams as well as special structures related to the transmission and conveyance of water, wastewater, and reclaimed wastewater.

For CSOs, we offer experience in environmentally mandated remedies geared to specific objectives of the control program and characteristics of the drainage area.  From actual separation of sewer and stormwater collection systems to area-wide storage and transport remedies, our comprehensive services meet our clients’ needs in controlling wastewater in the most cost-effective manner possible.

In addition to pioneering the new generation of environmentally superior ocean outfalls that are tunneled beneath the ocean floor, Parsons Brinckerhoff has a long record of meeting strict environmental regulations that govern the design, construction, and operation of all types of water, wastewater, and reclaimed water conveyance structures.