Just an update for all on this one. I visited the spot, 2 + blocks from the grade school. Indeed bees in the base of street tree. Rang the bell of the house, but no answer. Need to talk to the residents before I invest any time into it. It will need to be a trap out, but maybe some Honey Wrangler will coax them out.
It was a classic wound on the tree, likely years ago, and likely from over aggressive weed removal, that created some rot at the root flare where the bees are now entering. Tree looks healthy otherwise, as the does the colony.
Cheers, Phil