Where’s your main water valve located? Just past the meter? At the house? If you shut your main valve then it sounds like the leak would be before the valve and after the meter. Do you have “water hammer” in your pipes? Those can cause movement in the pipe and rupture the pipe in the slab. Is that what happened before?

If it's still spinning with the main water valve off, it has nothing to do with anything in your house. As jrb said, it's between the meter and the main valve.

But in answer to this unrelated question:

when I turn the valves off underneath one sink, hot water still runs out a bit (even after letting it run 30 min). Would this indicate a leak??

If you shut off the valve under the sink and turned the faucet on and it still flows, that just means that the valve isn't fully closed (and maybe it can't fully close). But if the hot water is stopped when you shut off the faucet, then there is no leak out of the system. The faucet is closing properly.

It might be something to get fixed (ie replace the valve under the sink) if you are getting a plumber out for some other work, but it isn't anything to worry about and nothing that you have to proactively fix.

Thank you all. I am not sure what water hammering is. One plumbing tech did confirm that it sounds like the leak is between the house and meter. He is not able to come out to look at it until tomorrow.

Any idea what the cost of this kind of repair will be??

(What are the odds that we would have TWO underground leaks discovered at our house in one year?? :( This has been a nightmare.)

Water hammering - "It is not uncommon for metal pipes in a plumbing system to bang loudly when a faucet is shut off suddenly, or when a water-using appliance such as a washing machine or dishwasher shuts off the water intake abruptly. The condition is commonly known as water hammer. The technical term is hydraulic shock, and it occurs when water stops or changes directions suddenly. The banging you hear is caused by the shock wave that causes plumbing pipes to move and strike against one another or against wooden framing members.

In addition to being annoying, water hammer can be so forceful that it can break pipes or loosen plumbing joints'

The prior leak was a wake up call to do a complete repipe. Pipes in slabs have a finite lifespan. Yours has been exceeded. Pay attention this time. Replumb everything.

My neighbor across the street had a leak between the meter/shutoff at the street and the house. I watched the guys bring in a big rig to run a new copper pipe from the street into his house. They said it developed pinhole leaks. Total estimated price for repair: $6500.

Do you have sprinklers? Underground sprinkler leaks can go undetected until you get a huge water bill!

I had a silent leak in a toilet that more than tripled my water bill for months! I have my bills set up on autopay thru my bank and it took me a few months to even notice it. Ughhh.