Mayor Mike McGinn said today that a dispute over cost overruns for a deep-bore tunnel under downtown must be resolved this month, and he will veto any bill that sticks the city with surplus expenses, as state law stipulates the city must.

"This month," McGinn said, "is the critical point that the council and mayors office, speaking on behalf of Seattle citizens, will say if we should go forward. I think we have to ... say that we shouldn't go forward with that risk." But if the council passes an ordinance that commits the city to pay cost overruns—which appears likely—he will attempt to block the measure by vetoing the bill.

Why the sudden urgency? According to the state's time line, the Washington State Department of Transportation will issue requests for construction bid proposals on the tunnel by May 28. Before that happens, the city must sign a final memorandum of agreement on the terms of that contract, which is currently being hashed out by the state's and city's transportation departments, and the city is essentially stuck with that deal.

And overruns plague tunnel projects around these parts: 30 percent on Sound Transit's Beacon Hill tunnel, 56 percent on the downtown bus tunnel, 24 percent on the Brightwater sewage tunnel so far. A 50 percent cost overrun on the deep bore tunnel would put Seattle with a bill for $1.5 billion—which is 27 times larger than the city budget shortfall for next year.

"Don't you wish that someone at Washington Mutual had said maybe we shouldn't make those subprime loans?" McGinn said. "That is where we are right now," he added, drawing an analogy between the fallout of the failed bank and the future debt of an expensive mega-project.

The solution would be, most likely, asking the legislature to amend state law, thereby putting the state on the hook for any overruns. While this is probably unrealistic—the legislature wouldn't touch it this winter, McGinn didn't push the issue with the legislature, and some on the city council argue the provision is unenforceable—McGinn is distancing himself from any future debt by vetoing the bill.

The city council, for its part, looks content with state law that puts Seattle on the hook for cost overruns; last fall, they unanimously passed a preliminary agreement to comply with the state law. "I think the agreement is consistent with what we passed last year," says City Council President Richard Conlin. "I think the council would adopt it." The council could override the mayor's veto with six or more votes.

It's unclear what exactly will happen next. The transportation departments for the state and city must draft the bill—which the state is required to make sure contains the cost overrun provision—and send it to McGinn. This is expected to happen by late May. The mayor could remove the cost overrun provision and then send it to the council, which would have to insert that language back in. Politically, that would distance himself from the fallout, if there ever is one.

"We should be clear, I don’t like the tunnel. I never liked the tunnel," McGinn said. But, he adds, "If the city council votes to proceed under any circumstances, I am bound by their vote."