This post has been updated.

That sound you hear is Mayor Kevin Faulconer and his allies laying the groundwork to argue that investing money from the city’s general fund into a new football stadium for the Chargers will not leave us lacking in other services — firefighters, police, library or recreation center hours.

Friday, Mary Lewis, the city of San Diego’s chief financial officer, sent a memo to the City Council updating them on how much the city has to spend every year on Qualcomm Stadium. Not only that, she tallied how much the stadium would cost were we to keep it operating for 20 more years.

It’s not pretty.

San Diego taxpayers are set to spend $14.1 million this year on stadium operations. That’s after we account for revenues the stadium earns from events and the minimal if non-existent rent the city collects from the Chargers, Aztecs and others.

Here’s Liam Dillon’s wonderfully readable explanation about why taxpayers lose so much each year on the stadium. We still owe more than $52 million on the debt the city took out to renovate Qualcomm Stadium in the late 90s. All kinds of rent credits and city mistakes mean the Chargers don’t pay rent. And events at our stadium — and across the country — don’t really make cities much money. Lewis’s numbers include what it costs for firefighters and police to manage large events at the stadium.

Lewis also estimated though that taxpayers would have to spend more than $280 million to keep the stadium operating for 20 years.

You have to be seeing it by now, yes? The mayor will soon reveal his plan for paying for a new stadium that uses general fund dollars. The big number total he presents will be less than that $280 million and he’ll say, “See, it is a better deal!”

Key to that being true, however, is to ensure the city doesn’t lose the same amount every year on the new stadium. If it did, we would double our loss. When the mayor’s task force came out with its plan, the National University System Institute for Policy Research estimated we would lose $11 million or more per year in the same way.

Why? The task force had the Chargers paying big annual rents. But that money would go to paying off debt to build the stadium. That meant the city was on the hook for operations and maintenance. The task force insisted we’d make so much money on events we could easily make up the difference but that was just rhetoric. The new stadium would not have a roof so that limits the events it can host and other venues across the country are hardly making big money on their similar stadiums.

No matter what happens and how much debt we take on to build a new stadium, we would still have to make the annual payments on the old stadium. Meaning we could join the elite group of cities still paying off stadiums that no longer exist.

The mayor has likely anticipated the worry that the new stadium would not be free to operate. Thus they have probably said the Chargers will have to handle all the operating and maintenance expenses for the stadium.

That would be not be a bad deal for the taxpayers. Of course, the Chargers are hardly on board with it. Ironically, this basic argument — that the city loses so much general fund money on Qualcomm it should be comfortable repackaging that for a new stadium — was first deployed by the Chargers.

Regardless, prepare for that rhetoric: General fund money for a stadium would not be worse than what we’re already paying.

Of course, if they left, we could use what we’re already paying for anything we want.

Correction: This post initially said the city’s is spending $12.8 million this year to run Qualcomm Stadium, a figure which left out some capital costs.