After being idle for seven weeks, MWRA's eastbound Tunnel Boring Machine (TBM) has resumed its 6.6 mile underground journey from Framingham to Weston, mining almost 750 feet since it began mining again on April 14.
The TBM is one of three massive machines mining MWRA's MetroWest Water Supply Tunnel, a 17.6 mile deep rock tunnel, which when completed, will serve as the main artery to carry drinking water for greater Boston residents from Marlborough to Weston. To date, almost 10 miles of the 17.6 mile tunnel have been mined. The $728 million project remains on budget and on schedule to finish in 2003.
The eastbound machine has been out of operation since February, when the machine's main bearing failed. Shea-Traylor-Healy, MWRA's contractor for this portion of the project, developed and implemented a plan to replace the bearing in the cramped quarters of the 16 foot diameter tunnel, 400 feet underground.
"MWRA staff, CM staff, contractor staff and union staff all pulled together and did a terrific job of safely performing a very difficult task. We are impressed and pleased with everyone's efforts under the circumstances," said MWRA Deputy Director of Capital Construction Michael J. McBride, P.E.
Anticipating the possible failure of the 11 foot diameter, 26,000 pound bearing, which is under constant stress, as it mines through solid bedrock, MWRA had earlier required its contractor purchase a spare.
"Having the spare bearing available kept the down time to only seven weeks instead of the six months it would have taken to obtain a newly manufactured one," McBride said. "On jobs like these, time is money, so the prompt repairs translate into significant savings."
The new tunnel is the backbone of MWRA's 10 year, $1.7 billion Integrated Water Supply Improvement Program. In addition to the tunnel, MWRA is building the new Walnut Hill Water Treatment Plant, consisting of modern ozone disinfection and corrosion control facilities that will improve drinking water quality and drastically reduce the amount of chlorine used in the system; constructing five new covered water storage tanks that will replace existing open reservoirs to protect the treated water; increasing watershed protection measures around MWRA's two source reservoirs in central Massachusetts, the Quabbin and Wachusett; and undertaking an extensive program to rehabilitate the large pipelines that deliver water to MWRA communities.
Created in 1985 by the Massachusetts Legislature, MWRA provides wholesale drinking water and wastewater services to 61 cities and towns in eastern Massachusetts with a population of more than 2 million people.