Sinkhole spotted in Seattle

A sinkhole roughly 30ft (9m) wide and at least 15ft (4.5m) deep has been found near the alignment of the Brightwater tunnel in Bothell, Washington, near Seattle. It was not clear how long the hole had existed.

"It's so close to the Brightwater alignment that it's pretty reasonable to assume that it's related to Brightwater," said a spokesperson from King County's Wastewater Treatment Division.

The 13-mile (21km) conveyance tunnel was part of the county’s project to build a new regional wastewater treatment plant called Brightwater.

Originally a joint venture of Vinci/Parsons/Frontier-Kemper had been working on the tunnel with Herrenknecht TBMs, which were both damaged and operations shut down in 2009. One machine was repaired and completed the excavation from Kenmore to Bothell.

Two years ago, a sinkhole with similar dimensions formed under a Kenmore resident’s driveway.

A Jay Dee/Coluccio JV replaced the original contractor for the remaining 1.9-mile (3.1km) segment using a Lovat TBM.

King County is waiting on a permit to fill the sinkhole.