NEW YORK (CBSNewYork) – The MTA says it has finally identified the cause of a sickening smell in L train subway stations.

According to lab tests, authorities say the smell that has lingered for days is diesel fuel. The MTA claims it may have come from an abandoned gas station fuel tank.

MORE: Transit Union Says Workers Sickened By Mysterious Lingering Odor On L Train

The transit agency added that crews are working to clean the fuel from the track drainage system and pumps.

Twenty large fans have also been placed in the tunnels to push out the smell. Although transit and city officials have claimed the fumes are not harmful, air quality testing is still ongoing and MTA workers have been caught wearing heavy-duty breathing masks.

MTA employee wearing a breathing mask in an L train station overpowered by mysterious fumes. (Credit: CBS2/TWU Local 100)