Updated 06/12/14 – 1:23 p.m.

CHICAGO (CBS) — Blue Line trains have resumed service between Rosemont and O’Hare International Airport, after the airport station was closed for nearly four hours due to an ammonia leak.

The O’Hare terminal closed shortly before 9 a.m. after ammonia fumes were detected. Hazardous materials crews found an ammonia leak in a storage room, and part of the area was evacuated as a result.

While the station was closed, CTA shuttle buses transported passengers between O’Hare and the Rosemont stop on the Blue Line.

Normal service resumed around 12:40 p.m. after the leak was secured and cleaned up, though shuttle buses continued running until 1 p.m., and the CTA said minor delays could continue in the early afternoon.

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