MSD spokesman Lance LeComb says several hundred thousand gallons of sewage have spilled from the broken main. The total size of the spill won't be known until repairs are complete.
The actual repair work will being around midnight Wednesday, and is expected to take four to six hours. If the work cannot be completed tomorrow morning, crews will have to wait until midnight Thusday before resuming work.
Authorities are investigating the death of a man found unresponsive while working inside a sewer in suburban St. Louis.
Police in Maryland Heights say 46-year-old Daniel Accola of Robertsville died at a hospital shortly before 11 a.m. Monday. That was about an hour after he fell ill with a co-worker in a new sewer line about 18 feet underground.
The other worker managed to make it out of the manhole under his own power.
Authorities say it's not immediately clear what caused Accola's death.