BOSTON (AP) – Water continues to leak steadily into a Big Dig tunnel, a new analysis shows, despite claims by Massachusetts Turnpike Authority officials that the problem is under control.

The analysis by an independent engineering firm contradicts a Turnpike report last month that said water discharge from the Thomas P. “Tip” O’Neill Jr. tunnel – a section of Interstate 93 beneath downtown Boston – decreased by half between 2003 and 2006.

Big Dig project manager Michael Lewis told the MTA board that reduction indicated the leaking was at least under control. But new state Transportation Secretary Bernard Cohen asked consultant engineers to look at the data, which they described as “at best … ambiguous.”

The engineering firm of Wiss, Janney, Elstner Associates Inc. reported that Lewis’ data “does not in our opinion support the claim that water seepage rates have been declining over the past three years.”

Eight million gallons of water were discharged from the O’Neill tunnel pump stations in the first half of 2005, compared with 7.5 million gallons in the first half of this year, the engineers said in their report. There were 6.5 million gallons discharged in the first half of 2006.

The Turnpike Authority board meets Tuesday, and member Mary Connaughton said she wanted to know why there was such a disparity in the numbers.

“This is an issue that certainly needs resolution,” she said. “It’s very important for the Turnpike Authority board to get the most accurate information as possible.”

Spokesmen for Cohen and the Turnpike Authority said Bechtel/Parsons Brinckerhoff, the private company that oversees the Big Dig, provided much of the information for Lewis’ report last month. Neither Lewis, nor Andy Paven, a spokesman for Bechtel/Parsons Brinckerhoff, returned calls left Monday by The Associated Press.

Bechtel/Parsons Brinckerhoff is currently negotiating with state Attorney General Martha Coakley as part of her cost-recovery investigation into faulty work in the project, including the leaks in the tunnel.

Connaughton credited Cohen for calling in “an objective third party” to look at the numbers.

“I place a great deal of weight on the conclusion they draw,” she said. “Having an independent consultant come in was a good thing.”

Cohen spokesman Erik Abell did not answer questions about the disparity in the numbers, but said: “We will also continue to carefully evaluate any and all information supplied by Bechtel/Parsons Brinckerhoff.

There is no imminent safety concern, he added, but the leaks can lead to long-term corrosion.

Leaks have plagued the $14.798 billion project – the most expensive public works construction in U.S. history – since it buried Boston’s Central Artery in a tunnel system. A massive leak into the O’Neill tunnel in September 2004 backed up traffic for miles.

Leaking is common in large tunnels, officials say, and most of the time motorists wouldn’t know about it. The leaks drain into holding areas below the surface, and pumps discharge the water.

After the massive leak in September 2004, inspectors looked at each of the approximately 2,000 underground wall sections in the I-93 tunnels, discovering 169 defects. The majority of those panels required minor patching while another 42 needed more extensive repairs.

AP-ES-08-20-07 1625EDT