Steve,

I assume you're referring to using a gun. I live in an area where it
is illegal to discharge a gun. Additionally, it would not be a very
effective remedy as:

01) it doesn't address the damage already done
02) you would have to wait too long to shoot them
03) shooting them may not get all of them

I would rather come up with a way to discourage them from burrowing in
the first place. I have a Rat Zapper, an electronic device that
electrocutes chipmunks and other similar size rodents. I will use the
Rat Zapper to attempt to control the chipmunks in addition to whatever
method I decide to implement to discourage them from burrowing around
my stoop.