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Has Big Dig Become Big Drip?

The Big Dig — Boston's newly opened $14.6 billion highway tunnel project — has a seriously flawed wall that contractors knew about as early as 1999, and is riddled with hundreds of smaller leaks, consultants reported in another embarrassment for the builders and the city.

Repairing the wall alone could take months and will probably require the closing of some traffic lanes overnight, officials said Wednesday. They had no immediate estimate of how much the repairs might cost.

The problems were identified by a team of outside engineers hired by the Massachusetts Turnpike Authority to investigate a major breach that caused a flood in September.

Turnpike Authority Chairman Matthew Amorello said that the tunnels remain structurally sound, a certain amount of leakage is inevitable, and the drainage system is keeping water off the roadways.

"There is no public safety issue," he said.

Nevertheless, it was more bad news for the Big Dig, the last major leg of which opened less than a year ago. The project — the most expensive highway project in U.S. history — was five years late and billions of dollars over cost, and has been plagued by allegations of fraud, waste and mismanagement.

"Somebody obviously messed up big time," Gov. Mitt Romney said. "And that's just one more example of a long list of blunders related to the Big Dig."

The investigation was ordered after a wall panel in September sprang an 8-inch leak, flooding the northbound Interstate 93 tunnel and causing a 10-mile backup. George Tamaro, an engineering consultant hired by the Turnpike Authority, said the most likely culprit was foreign material that got mixed in with the concrete.

The team of consulting engineers also said it found documents showing that managers of Bechtel/Parsons Brinckerhoff, the private consortium that oversaw the project, were aware that the wall was faulty when it was built in the late 1990s but did not tell the Turnpike Authority about it.

Amorello said the hundreds of leaks found during the investigation are smaller and unrelated to the problem in September, and the costs of fixing them are already built into the cost of the project.

As for the breached wall, he said the repair cost would be covered not by the taxpayers or toll-paying motorists, but by contractor Modern Continental or Bechtel/Parsons Brinckerhoff.

Bechtel/Parsons Brinckerhoff and Modern Continental defended their work.

"In a tunnel of this construction type, seepage is inevitable, but is mitigated by proper engineering and maintenance programs, which have been planned for and are in place," Bechtel/Parsons Brinckerhoff said. "The tunnel is structurally sound."

The Big Dig replaced the elevated Central Artery of Interstate 93 with underground tunnels through downtown Boston. It also connected Interstate 90 — the Massachusetts Turnpike — to Logan Airport, and added the Ted Williams Tunnel beneath Boston Harbor.

In 1985, during the design phase, the first cost estimate came in at $2.6 billion. Six years later, when construction began, the cost had more than doubled. And by 2000, project managers were fired after it was revealed they were hiding the true cost.