Gaps in compacted filler grout, or cement, may have allowed water and debris to seep onto the steel lining tube of an under-construction wastewater tunnel, leading to instability, according to the key finding in an in-depth report about what caused the tunnel to breach on July 9, 2025, temporarily trapping workers underground and indefinitely stopping the ambitious, yearslong project.
The Clearwater Tunnel Project launched in 2019 and had proceeded with no issues. But nearing its final ending point, a tunnel breach occurred at the 5-mile mark under Western Avenue, in San Pedro. It trapped 31 workers who were subsequently rescued safely after they were able to climb over the top of a fallen sediment pile, where there was still space, and then walk to the entrance of the tunnel several miles north.
The more than $600 million project has been stalled since the breach occurred as investigators have tried to find out what went wrong.
The key finding in the more than 700-page-long “Hatch Report,” which was released on Friday, Nov. 13, points to gaps in compacted filler grout, which is packed in to encase the tunnel’s steel lining tube, allowing water and debris to seep, leading to the instability. That is now the center of what is anticipated to be a long and detailed process to safely resume work on the project, which was within only a mile of its final destination.
The independent report looked at the factors that caused the breach. It was produced by Hatch, an engineering consultant in Long Beach that was hired by the Los Angeles County Sanitation Districts, which had spent years designing, planning and executing the project to replace too-small wastewater pipes with larger underground infrastructure to carry water to the ocean. The older system remains intact and is still operational.
But for now, work on the new system is indefinitely paused.
“We have zero projections about when work can start again,” Sanitation Districts spokesperson Michael Chee said in a Friday phone interview.
The breach, which is some 394 feet beneath Western Avenue, just south of Weymouth Avenue, occurred when the infrastructure was only about a mile from its final destination at White Point/Royal Palms Beach in San Pedro.
The entrance to the tunnel is adjacent to the A.K. Warren Water Resource Facility on South Figueroa Street, north of Lomita Boulevard.
“Our hope was that we’d be having a celebration at the beach this past summer,” Chee said on Friday.
The incident has also sparked some legal maneuvering, with one worker filing a claim against the contractor the county hired to construct the tunnel. The sanitation agency tapped Flatiron Dragados to construct the tunnel. The Hatch report said apparent irregularities around the site were spotted by Flatiron in the days before the breach.
Warning signs were there, the Hatch report said, with signs of “deformation and stress.” The report determined that more aggressive measures should have been taken to reinforce the tunnel. The primary finding, the report said, was that the most likely cause was that not enough cement had been injected into the crevices in the beginning.
It has been determined that dirt, rocks and water have filled the impacted portion of the tunnel in the aftermath, with workers conducting efforts from above to remove the debris, captured in images using high-tech drone technology sent below the street’s surface over the course of several months.
“In retrospect,” Chee said Friday, “there was information that would have been helpful if certain facts were brought to our attention.”
Flatiron Dragados could not be reached for comment on Friday. The company is now conducting drone imagery below Western, beyond the breach site, where no other inspections have yet been done to determine what the condition is moving ahead, Chee said.
The condition of the project’s electrically powered tunnel boring machine is among the main concerns, as it still sits buried just ahead of the breach, he added.
“We assume it’s underwater,” Chee said. “I don’t think we’ve put any stake in the ground in terms of a timeline (for when work can restart). The primary focus is on safety.”
No surface movement has been detected along the pipeline’s route, he said, noting that surface monitors have been installed in the area to signal any issues at street level. The tunnel route was originally mapped so it would not pass under homes or structures but would follow beneath streets.
The report was posted on the Sanitation Districts’ website late Friday.