Today I finally saw where the groundhogs I've been seeing live. I've seen the large holes going under the greenhouse/art room but didn't know for sure what was using them. I really hate the tunnels they dig. When it rains, it collapses the tunnels and then provides a small ditch for water to run through, rapidly increasing in size. The tunnels mess up a yard, provide tricky footing for people trying to walk through the yard, and I've found snakes in the tunnels, too.
I know for sure there were four groundhogs, but there may be more.
I copied and pasted the following from wikipedia:
Groundhogs are excellent burrowers, using burrows for sleeping, rearing young, and hibernating. The average groundhog has been estimated to move approximately 1 m3
(35 cu ft), or 2,500 kg (5,500 lb), of soil when digging a burrow.
Though groundhogs are the most solitary of the marmots, several
individuals may occupy the same burrow. Groundhog burrows usually have
two to five entrances, providing groundhogs their primary means of
escape from predators. Burrows are particularly large, with up to 14
metres (46 ft) of tunnels buried up to 1.5 metres (5 ft) underground,
and can pose a serious threat to agricultural and residential
development by damaging farm machinery and even undermining building
I realize other people may be fine with wildlife living under their buildings. I had a student who told me that a mother skunk had had babies under their front porch. I ask what they did about it. She said they fed them.