What Blocked Seattle Tunnel: A Lowly Pipe

The mystery underground object that had been blocking the giant Big Bertha tunnel boring machine under Seattle turns out to have been something pretty boring: An 8-inch diameter steel pipe. Seattleites had been fascinated by the mystery, speculating that an old steamship, locomotive, or other relic from the city's past was in the way, NBC reports.

The pipe wasn't even that old, having been placed there in 2002 to study groundwater movement, and the city is now wondering why it was left behind and how something so small could stall a $3.1 billion project and a five-story machine, the New York Times reports. Tunnel-boring machines are designed to go through rock and "don't react well with metal," according to transportation officials who say they are now focused on resuming drilling as quickly and safely as possible. (More Seattle stories.)