They've been at it for a couple of hours, and have made vastly more progress than I was able to make in quite a few hours of manual digging. Part of this is that they've got a small electric jackhammer, but it's clear that a fair bit of this is simply that they're better at it than I was.
Which just goes to show that "unskilled labor" involves skills too.
Crossposted from Dreamwidth (original here), with comments. Comment here or there; comments here will eventually be duplicated to there.