frozen water line in alley.

[Account Closed]

Asking BP members for any recommendations on thawing a frozen water line in an alley that is between the first water valve of a 4 plex and the 2 nd water valve. Each water valve flows to 2 apts. underground, the first 2 apts. have water the 2nd 2 apts. have the frozen water approx. 3-4 ft. underground. Cant dig water line up as ground is frozen. But have been told by a plumber that a ground thaw machine would thaw ground at a foot per day to unthaw pipe. Has anyone heard of this or know of something else to try, tenants have been w/o water fro over 2 weeks now, looking for a solution as city is no help.