SEATTLE — The Washington State Department of Transportation believes it has identified the cause of a water leak in the State Route 99 tunnel under downtown Seattle, though a permanent fix is still pending.

Water was discovered leaking on cars in the southbound lanes of SR 99 on Feb. 14. Crews with WSDOT took a look at the issue during planned overnight maintenance and routed water towards the drainage system. 

WSDOT officials think the moisture is coming into the tunnel through a grout port, which is a location used during construction to inject grout into the ground surrounding the tunnel walls, to fill in space.

Water resistance is part of the tunnel's design and WSDOT officials said there is no danger to commuters. Gaskets at the edge of the ring pieces seal together during construction, which is critical because it passes below sea level through very wet soil.

RELATED: Water leaking from ceiling of Seattle's SR 99 tunnel onto southbound lanes

WSDOT wasn't able to say if it's salt or freshwater but they do not believe it's related to recent rains and flooding.

The agency is waiting for a work plan from the contractor to repair the leak since the tunnel is still under warranty. They hope that permanent repairs could take place next week.