Thirty-one workers in Los Angeles narrowly escaped tragedy on July 9 after an outfall effluent tunnel still under construction partially collapsed, threatening to trap them 370-feet below street level in the dark.
The 18-foot diameter tunnel in the L.A. neighbourhood of Wilmington is part of the nearly $700-million Clearwater Project designed to carry treated effluent to the Pacific Ocean. A portion of the tunnel, which is not expected to be in service for several more years, collapsed at approximately the five-mile mark, project officials announced in a statement.
All of the workers were able to climb through and over debris and safely exit the tunnel some 9.6 kilometres to the nearest exit without major injuries. While the workers had access to an underground transport vehicle, the Associated Press reported that it was only able to travel a short distance before it was blocked by debris.
“We are working directly with the contractors to conduct a full investigation of the cause of this incident,” Clearwater Project officials announced in a July 10 statement. “The investigation will look at the safety, engineering and structural integrity of the tunnel and has already begun. Clearwater Tunnel operations have been halted while this investigation takes place and there is no timeframe for how long the process will take.”
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Emergency response teams from the Los Angeles Fire Department, including urban search and rescue units, responded immediately and assisted construction crews onsite with successful rescue operations.
The shaft site and point of access for the tunnel is located on property owned by the Los Angeles County Sanitation Districts, adjacent to the A.K. Warren Water Resource Facility, which receives and treats wastewater from approximately 3.5 million county residents.
The Clearwater tunnel project, which uses a tunnel boring machine, is being constructed by Flatiron West and Dragados USA, operating as a joint venture under contract with the Los Angeles County Sanitation Districts.
The Clearwater Project began in 2006. Existing tunnels in the area have come close to exceeding capacity, prompting the need for a replacement.
