HARTFORD -- A state Department of Transportation official Friday told lawmakers that officials have negotiated a preliminary deal for Exxon Mobil to pay for the cleanup of environmental contamination at the state's highway service plazas.

"There is a draft agreement," Charlene Casamento, chief of the DOT's Bureau of Finance and Administration, told Gov. M. Jodi Rell and other members of the state Bond Commission.

Commission members subsequently voted to borrow $4.8 million to begin the work, with the understanding that money will be repaid by Exxon Mobil.

The cleanup is a direct consequence of the 35-year contract Rell and the DOT signed in late 2009 with Project Service LLC, a partnership between Subway sandwich shops and the Carlyle Group, to renovate and operate Connecticut's 23 service plazas.

Critics who felt Rell gave up too much direct revenue from the previous arrangement with Exxon Mobil were also concerned the state might have to foot the bill for millions of dollars of environmental cleanup.

The DOT at the time assured legislators it was holding Exxon Mobil, which has sold gasoline at the plazas for around 30 years, financially responsible.

But the agency undercut that assertion when it was learned it had unsuccessfully attempted to convince Project Services and a competitor for the service plaza contract to take on the cleanup responsibility.

"I'm trying to understand whether there's any fundamental disagreement" between Exxon Mobil and the state, said Rep. Cameron Staples, who, as co-chairman of the Legislature's finance committee, sits on the bond commission.

But Casamento said Exxon Mobil has, "been at the table, willing to take on their responsibility." In that case, asked Sen. Andrew Roraback, R-Goshen, another Bond Commission member, "what is there to negotiate?" DOT has declined to specify the extent of the contamination or the estimated cleanup costs beyond the $4.8 million.

A state report published in September 2008 concluded there were issues with groundwater contamination at many of the service plazas and leaky underground fuel storage tanks at 15 of the 23 locations.

But Casamento did not want to get into details of the draft agreement with Exxon Mobil.

"Clearly, they're responsible for any pre-existing contamination," Casamento said.

Earlier this week Gov.-elect Dan Malloy expressed concern that the $4.8 million "might be the first of many appropriations needed for cleaning up Exxon Mobil's contamination of these sites." Asked afterward for additional details, DOT spokesman Judd Everhart said, "There's a (cost) number in the draft and that is the number we believe will cover the costs of the remedial work." The draft agreement requires final approval from Attorney General Richard Blumenthal's office.

Blumenthal, in a statement Friday afternoon, said, "My office is working closely with the Department of Environmental Protection to ensure we reach the best possible agreement to remediate and pay for contamination at (the) rest stops and fully protect taxpayers. The negotiations are continuing and we cannot comment further." A DEP spokesman also declined comment.

Despite the lack of details, Staples afterward said he was satisfied with Casamento's comments.

Staff Writer Brian Lockhart can be reached at brian.lockhart@scni.com