A tunnel in Tysons Corner that will hold the new Silver Line has sunk into the ground about an inch but is still big enough for trains to pass through and won't hurt the project, a new inspection shows.

Engineers say the floor of the tunnel has "settled" into the ground by about an inch at its worst part, but there's still enough clearance overhead for Metro trains to use the tunnel, said Silver Line project manager Pat Nowakowski.

Nowakowski said he still has to review the analysis done by his contractors, a coalition called Dulles Transit Partners and led by Bechtel, but that he thinks the tunnel won't be a problem.

"At this point the report looks as if everything is OK," he said. "We are currently looking at [the report] now to determine whether or not we consider it accurate."

Nowakowski said he doesn't know why the tunnel settled and that theories would be only speculative.

"In my mind at the end of the day it doesn't really matter," he said. "The bottom line is it happened, and we need to make sure that it's OK."

Engineers first noticed the tunnel lowering in February 2012, but it stopped by May.

The first phase of the Silver Line, to Reston through Tysons Corner, is expected to open at the end of the year.