MWRA TBM crew holes through on critical Boston CSO tunnel project.

The Massachusetts Water Resources Authority has notched another successful tunnel-boring operation, its fifth in 20 years. The latest is a 2.1-mile-long storage tunnel, part of a 15-year combined-sewer-overflow program totaling $850 million.

The 19-ft-wide, 17-ft-finished- dia., $148-million North Dorchester Bay Combined Sewer Overflow Tunnel will virtually eliminate closures at Carson Beach in south Boston. The tunnel runs from Conley Terminal to near the Bayside Exposition Center and will hold 19-million gallons. The tunnel was designed by Parsons Brinckerhoff/Metcalf & Eddy and built by the joint venture of Shank/Balfour Beatty/Barletta.

“We used a soft-ground custom-made Hitachi TBM,” says Frederick A. Laskey, executive director, MWRA. “We had to thread a needle between the surface and bedrock, mostly through Boston blue clay.”

The one-year job started last September, and tunnel work will conclude this September. Phase Two—a pump station and an odor- control facility estimated at $35 million—will be let in November, for May 2011 completion.

A 55-ft-long, 50-ft-dia. mining shaft and a 40-ft-long, 34-ft-dia. removal shaft serviced the work.