On May 17, 2:15*pm, wrote:
For years I've had a woodchuck living under my shed, but I think a
skunk has been encroaching on his territory because my shed has the
distinct aroma of skunk foof.

I'm trying to determine if I have a skunk living there or a woodchuck.
I figure if the skunk just shot his load and left, the smell would
dissipate.

The smell does not seem to be dissipating...

Then I remember that skunk smell is pretty strong stuff.

How long does untreated skunk smell go before it starts to dissipate?

If it's on fabric or upholstery it could last pretty much forever.
Wood holds the stink for quite awhile, too. Metal and non-porous
surfaces can be de-stinkified more easily, but it sounds like you have
no way to get to where the skunk sprayed (under the shed).