Big Dig chooses repair for leak

Nine months after a gushing leak erupted in the northbound I-93 tunnel, Big Dig officials have picked the least expensive of three possible repair plans for the wall, according to a government official and a construction industry official briefed on the plan.

The plan calls for bolting a concrete-encased steel plate over the leak, which has been temporarily plugged since Sept. 15, when thousands of gallons of water poured into the tunnel and backed up traffic for miles.

That plan, which is expected to cost less than $1 million, is far less elaborate than the plan advocated by an outside engineering consultant, who recommended totally rebuilding the wall, from the bottom on the tunnel about 80 feet below the ground to the tunnel roof.

A third proposal considered by Big Dig officials called for pouring an entirely new concrete wall, which would be located just behind the damaged wall.

Matthew J. Amorello, chairman of the Massachusetts Turnpike Authority, which oversees the Big Dig, presented the plan for the steel patch yesterday to federal officials in Washington, according to Turnpike Authority spokeswoman Mariellen Burns.

Burns declined to provide details of the plan, saying it could change after input by officials of the Federal Highway Administration and the Department of Transportation's inspector general. The federal government is providing about half of the $14.6 billion cost of building the Big Dig.

''When we have a final plan, we will present it to the public," Burns said. ''We will not discuss it until then."

A government official briefed on the plan said Kenneth M. Mead, the Department of Transportation's inspector general, agreed to the plan yesterday. Calls to Mead's office seeking comment were not returned yesterday.

The work would take several weeks and result in some lane closures in the tunnel, officials have previously said. It would be paid for by construction contractor Modern Continental and Bechtel Parsons/Brinckerhoff, the designer and private sector manager of the Big Dig.

But any plan short of the one recommended by consultant George J. Tamaro, who was fired by the Turnpike Authority earlier this year, was met with skepticism yesterday by state Senator Steven Baddour, co-chairman of the Legislature's Joint Committee on Transportation.

''We have a right to be skeptical because Turnpike officials brought in the world's foremost expert on these kinds of walls and when they didn't like what was recommended, they fired him," he said.

''I think the Turnpike Authority has a lot of explaining to do on why they didn't accept Tamaro's plans," he said.

The leak resulted from groundwater pressure on a soft spot in the tunnel wall created by debris and extraneous material which were left in the wall during construction.

Tamaro's proposal called for reconstruction of the entire section of wall where the leak occurred -- with small sections of the damaged wall cut away one at a time and replaced with newly poured wall. Such an approach, he suggested, would preserve the integrity of the tunnel wall and result in a sounder structure. His plan also called for groundwater to be removed from the area adjacent to the wall, an idea criticized by some Turnpike officials and Bechtel/Parsons Brinckerhoff engineers as potentially damaging to the foundations of nearby buildings.

Tamaro could not be reached for comment yesterday. He and Jack K. Lemley, another consultant hired by the Turnpike Authority to work on tunnel leaks, were fired by the Turnpike Authority earlier this year. They complained they were not given access to records they needed to carry out thorough reviews of the leak problems, but Amorello said Lemley's contract had expired and Tamaro faced a conflict of interest and could not continue on the project.

Meanwhile, the investigation continues into other flawed sections of the Interstate 93 tunnels. So far, the review has turned up about a dozen significant defects in the walls, and about 150 other minor ones. Project officials have yet to put forth a plan for repairing those areas.

Sean P. Murphy can be reached at smurphy@globe.com.