What to know about the LA tunnel collapse

An effluent tunnel collapsed in Los Angeles at roughly 8:00 p.m. local time on July 9, 2025, trapping 31 workers underground. Workers were trapped approximately 5 miles from the sole vertical access shaft for an hour. 27 workers were trapped from the initial collapse, while 4 construction workers went in following the collapse to help the others.

According to CBS News, the Los Angeles Fire Department responded swiftly, sending all of its Urban Search and Rescue Teams.

All 31 workers were rescued with no visible injuries, according to CBS reporting.

“I just spoke with many of the workers who were trapped,” said Los Angeles Mayor Karen Bass in an X post. “Thank you to all of our brave first responders who acted immediately. You are L.A.’s true heroes.”

What is the Los Angelese Effluent Outfall Tunnel?

The 18-foot diameter tunnel collapse occurred at the $630.5 million Los Angeles Effluent Outfall Tunnel project, which is part of a broader project meant to protect local waterways called the “Clearwater Project.”

The Clearwater Project began in 2006, with a multi-year planning phase and environmental review effort. Officials planned on constructing a new tunnel that would be built to provide relief to aging infrastructure. Currently, two tunnels are used to convey water to the ocean. The existing tunnels were built in 1937 and 1958 and were not built to current earthquake standards.

According to the project website, the existing tunnels almost exceeded capacity twice during major rainstorms. If the combined capacity is exceeded, partially treated or untreated wastewater would be discharged into surrounding waterways.

Why is the tunnel needed?

The tunnel is part of a larger wastewater project, meant to convey water to the ocean with modernized infrastructure.

The Los Angeles Sanitation District operates and maintains the Joint Outfall System (JOS) which is the main sewer network that collects and treats wastewater from over 5 million residents. The Joint Water Pollution Control Plant (JWPCP) in Carson, uses two large tunnels to convey water to the ocean. One was built in 1937 and the other in 1958. The existing tunnels have come close to exceeding capacity, prompting the need for a new tunnel.

What caused the tunnel collapse?

Preliminary reports suggest that a structural failure in the tunnel lining led to the collapse possibly due to squeezing ground. The Los Angeles Sanitation District has halted operations and will conduct an engineering review.

“We are blessed that all of those men made it out and made it home to their families,” said Los Angeles County Supervisor Janice Hahn in an LA Times article. “Most people in the Harbor Area communities didn’t even realize that this tunnel was being bored beneath them, but these men go to work every night to build this critical infrastructure project for our region. I am so grateful that they are home safe tonight.”