The Massachusetts Water Resources Authority on June 25 awarded a $4.9-million contract to the Boston office of Stantec for engineering services on the 45-year old, 60-mgd West Roxbury Wastewater Tunnel. The 12-in thick cast-in-place concrete lining in the 12,500-ft long, 84-in dia. rock tunnel, which serves about 125,000 homes and businesses, is eroded due to hydrogen sulfide corrosion.
J.F. White, Framingham, Mass., will inspect the tunnel, which has two portals and a 220-ft deep shaft, this fall to help determine the extent of the problem and the relining solution. "The 12-in liner is structural and as of a decade ago the concrete was compromised for the first 1,500 ft from the New Haven Street junction chamber," says William B. Powers, Stantec project manager. "Other portions show only corrosion to the veneer." Stantec is working with local offices of Hatch Mott MacDonald for possible new tunnel routes and Brown and Caldwell for hydraulic modeling.
The corrosion problem was first discovered in 1999 and the chamber and adjoining portions of the Wellesley extension tunnel have since been rehabbed. Stantec is considering several options including: a 72-in dia. slip-lined pipe, in the dry CIP pipe, a segmental liner or possible realignment of the tunnel. Work possibly could go out to bid by Oct. 2012 for a June 2016 completion, depending on scope and solution. "We estimate it will cost about $90 million but it is a critically important part of our sewer system," says Fred Laskey, MWRA executive director.