Service was halted between the First Avenue Station in Manhattan and the Morgan Avenue Station in Brooklyn after riders reported "nauseating" smells of gasoline and burnt rubber.
The MTA traced the source of the smell to Graham Avenue in Williamsburg, and state Department of Environmental Conservation and FDNY crews determined it to be safe.
Authorities say non-flammable heating oil being stored somewhere near the subway tunnel leaked, causing the smell.
They say it was not gas, not fumes from diesel trains, not related to the overnight L train project, or to any other MTA construction.
Once the source was located and determined to be non-flammable, service was able to resume.
Full train service resumed in both directions around 3 p.m., but officials said lingering smells may be present at stations in that area.
It is estimated to dissipate as trains resume operating.
The MTA released the following statement:
"The MTA has restored full service on the L line. After an unusual odor was discovered, the MTA immediately launched an investigation. Service was suspended while FDNY and DEP thoroughly examined what appeared to be an oil or gas leak at the Graham Station, at track level. Both Departments have confirmed that non-flammable heating oil from an external source had leaked onto the track and the incident is completely unrelated to the L train project or any other MTA construction. Air quality at all stations has been tested and determined to be safe. We apologize to our customers for the delay in service - their safety is always our number one priority and we would never compromise it."
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