We had a family a number of years ago about 10 miles from here that had fowl smelling water. It came on all of a sudden from a farm well that was at least 50 years old. The TV news showed a match lighting it up. It would flame briefly before going out. The experts determined it to be swamp gas collecting in the well and flowing with the water. it was eventually filled with bentonite. They said it happens occasionally when the casing has a crack near the surface.