Service was shut down for nearly 12 hours Saturday, and a shuttle bus service was put in place.
CTA President Ron Huberman says riders should allow extra time to get to O'Hare because some trains will terminate at Rosemont.
CTA Blue Line train service between Rosemont and O'Hare will operate at reduced levels for the next month.Flooding in the tunnel Saturday caused a vault fire that damaged cables which control signals and switches leading into the airport station.