19 is way to cold... If the picture is your water line, try putting a compost pile on top of it, as a compost pile breaks down it generates heat... Might work?

Good Luck, Jeff

Since it froze up again, I think our first thing to try will be really sealing the crack with some of that foam insulation as Roland suggested. If that doesn't do the trick, I'll probably pile dirt on top for a longer-lived solution. Compost would definitely work, though --- I'd just have to remember to tend it....