A 21-ft, 8-in dia earth pressure balance tunnel boring machine has launched in Seattle to begin creation of a 2.7-mile-long tunnel that will store combined sewer overflow as part of the city's consent decree with the US Environmental Protection Agency.
A major portion of the city and King County Ship Canal Water Quality Project involves the creation of an underground storage tunnel to reduce the amount of polluted stormwater from rain and sewage flowing into the Lake Washington Ship Canal, Salmon Bay and Lake Union.