That's what I would do as well Bill. Throw a box or two of Baking Soda on
the area after you sweep the puddle out to neutralize the acid if you want.
Baking Soda is a base and it will neutralize the acid. Water is neutral
itself (neither acid nor base) and it can be used to neutralize the acid but
it will take more of a flush with just water than if you throw a little
baking soda to it. I'd sprinkle a box or two on the swept out puddle, sweep
it around a bit and then flush it well with water. Should be fine after
that.
--

The acid you use for etching cement is probably HCl, which ought to react with
the
cement to produce mostly calcium cloride (a salt) and free hydrogen.
Nuetralizing the excess using backing soda, (sodium bicarbonate) should
produce sodium cloride, (table salt) more calcium cloride, and some free gasses.

The runoff will be salty water.

You might get high enough concentrations so to make it unpalatable
to wildlife, but you're unlikely to actually harm anything that doesn't
LIVE in the puddle. If you've got frogs in there, you might get high
enough concentrations to croak them.