BOSTON (AP) – Leaks in the Big Dig tunnel system are more widespread than state officials have acknowledged, and top construction managers warned as far back as 1998 about problems that could cause failures in tunnel waterproofing efforts, records show.

Documents obtained by The Boston Globe show there are nearly 700 leaks in a single 1,000-foot section of the Interstate 93 tunnels beneath South Station.

And project managers have collectively signed off on at least $10 million in cost overruns to repair the leaks and water damage since early 2001, the records show.

Earlier this month, a team of independent engineers hired by the state to investigate a massive September leak in the I-93 tunnel said the $14.6 billion Big Dig was riddled with more than 400 leaks throughout the tunnel system.

Project managers and state officials have insisted that the tunnels are safe for motorists.

The project – formally known as the Central Artery/Third Harbor Tunnel project – replaced the elevated Central Artery of I-93 with underground tunnels through downtown Boston, connected the Massachusetts Turnpike to Logan International Airport and added the Ted Williams Tunnel beneath Boston Harbor.

Attorney General Thomas Reilly said Wednesday it’s too early to assign blame for the leaks, but said the “problem is far broader than one person.” He said the cost of the repairs will run into the millions, and that parties, including the Turnpike board and the contractors hired to perform the work, need to focus on fixing the problem.

“We need these engineers to put their heads together and come up with a solution,” he said. “These companies have national and global reputations that are going to follow them from this project.”

Turnpike Chairman Matthew Amorello responded by naming a liaison between the project and the Turnpike board to help keep the board up to date with any new problems. The liaison, or ombudsman, will be given authority to look at documents and talk to anyone on the project.

John Christian, a geotechnical engineer, will hold the new post. Christian headed up a committee that released a report commissioned by the Turnpike last year recommending ways to save money and speed Big Dig construction by improving management and honing oversight.

Amorello also pledged to begin holding weekly press briefings to update progress on the project.

The new documents obtained by the Globe include memoranda, diagrams, photographs and correspondence pertaining to the Central Artery tunnels. They show that the Massachusetts Turnpike Authority, which oversees the Big Dig, and the project’s private manager Bechtel/Parsons Brinckerhoff established a Leak Task Force early in 2001.

They are currently allocating $250,000 a month to send repair teams into virtually all sections of the tunnels.

Project officials have acknowledged that as early as 1999, contractors on the costliest highway project in U.S. history knew that serious construction flaws existed in the walls of the tunnels directing traffic under downtown Boston.

However, an internal memo circulated by managers within Bechtel/Parsons and obtained by the Boston Herald, raised concerns in June 1998 that waterproofing at the roof and base of tunnel walls would fail unless leaks were repaired.

“Let’s keep the focus on the real culprit in this matter – and that is Bechtel/Parsons Brinckerhoff,” state Assistant Inspector General Jack McCarthy said Tuesday.

Doug Hanchett, a spokesman for the Turnpike Authority, said the agency has made progress in controlling the leak problem, and is working to recoup costs from contractors.

The problem with waterproofing the tunnels stems in part from an apparent project-wide failure in the original design – a critical feature of a tunnel that sits almost entirely beneath the salty water table of downtown Boston.

In a confidential report commissioned by the Turnpike Authority in 2001 by the auditing firm Deloitte & Touche, the Globe reported, project officials acknowledged that “the original design provided insufficient protection against leaking” at the top of tunnel walls.

Meanwhile, Gov. Mitt Romney is pressing ahead with his quest to fire Amorello, saying someone with more technical expertise is needed. But it’s not clear whether the governor can oust the former state senator because the Turnpike Authority is an independent authority and a majority of board members are publicly backing Amorello.