The independent engineering specialist who led an investigation into leaks at the $14.6 billion Big Dig (search) project says he can no longer vouch for the safety of its tunnels.

"I am now unable to express an opinion as to the safety of the I-93 portion of the Central Artery," Jack K. Lemley wrote in the March 9 letter to the Massachusetts Turnpike Authority (search), a copy of which was obtained by The Boston Globe.

The Big Dig project -- formally called the Central Artery and Third Harbor Tunnel project (search) -- buried Interstate 93 underneath downtown Boston and connected the Massachusetts Turnpike to Logan International Airport.

Citing what he called "a cover-up and stonewalling crisis," Gov. Mitt Romney (search) responded to the report by saying he would ask the state's highest court if he has the power to fire Massachusetts Turnpike Authority Chairman Matthew Amorello.

The Turnpike Authority oversees the system of bridges and tunnels that has been plagued for years by cost overruns, management problems and, most recently, hundreds of leaks in the walls of the Interstate 93 tunnels.

"With the Big Dig there's been a pattern of cover-up and stonewalling that has left the public with little confidence that the project is being managed well or that the road and tunnel system are safe to travel," Romney said.

A call to the Turnpike Authority was not immediately returned.

Romney stopped short of calling the tunnels -- the centerpiece of the project -- unsafe.

"I don't feel as safe in the tunnels today as I did yesterday," Romney said. "If (Lemley) doesn't know if the tunnels are safe then I don't either and that's intolerable."

Romney has previously called for Amorello's resignation, but the chairman has so far refused.