MORE INFORMATION MWRA Executive Director Frederick Laskey, Mass. EOEEA Secretary Ian A. Bowles, MWRA Deputy COO Charles Button, MWRA Sr. Construction Manager Kenneth Chin, US EPA Region 1 Administrator Robert W. Varney, MWRA Director of Construction Anandan Navanandan. Tunnel workers crawl through the TBM after the holethrough. "Massive Drill Surfaces in South Boston" a photo essay on Boston.com Boston Globe Image (George Rizer/Globe Staff)

This morning, the tunnel boring machine that has been mining underneath Day Boulevard in South Boston reached its destination and broke through the concrete shaft into daylight. Members of Local 88 Tunnelworkers then crawled through the machine’s face to greet their coworkers on the other side.

The mining began last November in a shaft at the Conley Terminal and ended 2.1 miles later in a shaft near the entrance of the Bayside Expo Center. This 17-foot diameter, 2.1-mile-long soft ground tunnel will hold 19 million gallons of combined sewer overflows and stormwater, eliminating discharges to the beaches in South Boston.

The $148 million project is being constructed by a joint venture of Shank/Balfour Beatty/Barletta.

A future contract will include construction of an odor control facility for the tunnel and a pump station and connecting force main that will allow MWRA to dewater the tunnel after storms.  The Morrissey Boulevard Storm Drain project is being designed and constructed by the Boston Water and Sewer Commission under agreement with MWRA.

For decades, combined sewer overflows have discharged about 21 times a year at six outfalls along South Boston beaches.  This project will eliminate CSOs to these beaches, except in a catastrophic storm event.  Stormwater drains also discharge to the South Boston beaches every time it rains - about 95 times a year.  The project will prevent stormwater discharges in up to a 5-year storm.

During wet weather, CSO and stormwater flows will be stored in the tunnel until the storm subsides.  The tunnel will then be pumped out and the flows sent to Deer Island for treatment and discharge.

After the project is constructed, beach closings will be a very rare occurrence - about once every 5 years.

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Updated August 13, 2008