Work on a Los Angeles County sanitation tunnel has been halted as investigators look into what caused it to collapse Wednesday evening, leaving 31 workers scrambling to make their way to safety. Los Angeles County Supervisor Janice Hahn, who is also on a county sanitation district board, said in a statement that the district will be looking into what caused the tunnel collapse. … The purpose of the Clearwater Project is to build a more robust tunnel so that treated wastewater can be safely pumped out to the ocean from the county’s biggest treatment plant. The existing tunnels can’t be taken out of service, were not built to today’s seismic standards, and are not large enough to handle high volume during heavy storms. A 2017 storm nearly flooded the system, and the damage from such an event could be catastrophic. If the existing tunnels were to fail, the Joint Water Pollution Control Plant would either discharge raw sewage into nearby Machado Lake or into the Los Angeles Harbor, with environmental impacts that could last months or years, county officials said.

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• AP News: Workers raced for miles in the dark to escape being trapped after tunnel collapsed in Los Angeles
• ABC7 (Los Angeles): LA County tunnel project flew mostly under the radar for more than a decade before collapse