BOSTON (AP) As the city sleeps, teams of men and women clad in white jumpsuits labor deep underground in the dark recesses of the Big Dig, waterproofing the tunnel where water drips and seeps.
There were four teams working in the cramped bays atop the Interstate 93 tunnel, where the walls join the roof, pumping rubbery grout into joints to stop the hundreds of leaks in the $14.6-billion system of tunnels, roads and bridges.
The Turnpike Authority brought reporters into the tunnel early morning, Dec. 3, to look at the waterproofing work that has been going on since the tunnel’s completion, and that will likely continue throughout its life.
But the seepage has lately become the topic of heated debate on Beacon Hill and elsewhere, further eroding public confidence in the mammoth highway project.
It began in September with an 8-in. breach in the tunnel wall that sent water gushing onto the roadway, backing up traffic for 10 mi. At a Statehouse hearing Thursday, Dec. 2, the Big Dig’s project manager, Bechtel/Parsons Brinckerhoff, apologized for not fixing the problem when it had the chance.
That leak, the result of a construction flaw that allowed the water to force its way through a fissure in the concrete, triggered a new wave of scrutiny that revealed hundreds of other, smaller leaks near the tunnel’s ceiling.
It’s these leaks — typical in tunnels of this type, according to Turnpike Authority Chairman Matthew J. Amorello — that are the focus of the nighttime waterproofing teams working beneath the city each night.
“There will be a waterproofing protocol for the history of this tunnel, just as there is in every tunnel everywhere,” Amorello said, standing in one of the narrow bays over the tunnel as water trickled down the wall.
The early morning tour gave an up-close look at the Big Dig’s troubleshooting. Turnpike Authority officials outfitted reporters and photographers in hardhats and orange vests, loaded them into vans and drove them into the tunnel, depositing them in the closed, leftmost two lanes of the northbound I-93 tunnel.
Then, the reporters were loaded onto a lift that raised them through the roof and into the overhead exhaust area called the plenum. From there, firefighters and workmen guided them through the gloom to one of the 500 or so leaking bays up against the tunnel wall.
Engineer John Smith pointed to where the groundwater seeped down the wall, leaving a brown sludge on the wall that resembles rust. He wiped it away with the tip of his finger.
The contractor that worked on this section of the tunnel, Modern Continental, had tried to seal the joint with thick layers of waterproofing material that looks like caulking, but the leakage continued.
Now, engineers are stopping the leaks by drilling holes into the old waterproofing, inserting a tube, then forcing quick-hardening grout into the holes using a hydraulic pump.
“We don’t want any water. We’re going to get them to a watertight condition,” Smith said.
After the reporters returned to the tunnel floor, where workers were preparing to shut down the waterproofing operation for the night, Amorello said over the roar of a generator that it was important that the public understand the difference between the leaks.
“The breach in the slurry wall was unacceptable, and it should not have happened,” he said. “The waterproofing effort that we have ongoing is to seal up these tunnels. Bechtel is responsible for delivering us a watertight tunnel, and our contractors are responsible for delivering us a waterproof tunnel. That’s what they’re working on.”
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