Who gets billed if the Seattle tunnel goes over budget?

SEATTLE – If the deep bore tunnel to replace Seattle's Alaskan Way Viaduct goes over budget, who will pay the extra dollars - the city or the state?
Over the weekend, Gov. Chris Gregoire and Mayor Greg Nickels formalized the tunnel agreement. But, there's a legally fuzzy amendment in the paperwork that says Seattle property owners will have to pay for cost overruns.
Can the state force its largest city to pay, and is that amendment legal?
Gregoire isn't concerned because she says the tunnel budget has been padded.
"We've already put in a 30 percent cushion for reserve and risk. We'll get it done so there's no need to talk about that," said Gregoire.
Rep. Judy Clibborn, D-Mercer Island, who wrote the amendment, knew at the time she put it in that it wouldn't stand up in court.
"There is no legal standing in that wording in that amendment," said Clibborn.
Both mayoral candidates, Mike McGinn and Joe Mallahan, say they'll work to kill the amendment if elected. The top lawyer in the state has privately told some lawmakers the amendment isn't enforceable. But, Attorney General Rob McKenna will not publicly state that in case he has to defend it someday.
So, when construction starts in 2012, it's not totally clear what the tunnel will cost or who will pay if the people who wrote the budget are wrong.
Also keep in mind that the tunnel is a state highway – a continuation of State Route 99. If the city is forced to pay the overruns, it could argue it is not legally obligated to build state roads.