A worker walks through a completed portion of the tunnel.

A modern tunnel boring machine (TBM) named Rachel has been quietly building an 18-foot diameter, 7-milelong tunnel from Carson to San Pedro. This tunnel will convey cleaned water from the Los Angeles County Sanitation Districts’ largest wastewater treatment plant (the Joint Water Pollution Control Plant) to existing ocean outfalls at Royal Palms Beach. This new tunnel is part of the Clearwater Project, which will protect local waterways by addressing critical aging infrastructure.

In 2012, the Sanitation Districts’ Board of Directors approved the Clearwater Project. The project is the result of a multiyear planning and environmental review effort to assess the reliability and future capacity needs of the main sewer system serving five million people residing in the Los Angeles Basin.

The Joint Water Pollution Control Plant (JWPCP), the hub of this sewer system, relies on two tunnels to carry clean water to ocean outfalls. The tunnels are 12-foot and 8-foot in diameter and 60- and 80-years-old, respectively. The new 18-foot diameter replacement tunnel addresses this aging infrastructure and will provide structural reliability, sufficient future capacity, and meet current seismic standards.

Rachel is 21 ½ feet tall and more than 2 ½ football fields long. She stops every 5 feet to put up prefabricated tunnel wall segments so that the tunnel wall is built as digging progresses. Overall, about 40 to 50 feet of tunnel per day will be constructed.

In 2020, a 60-foot diameter, 135-foot-deep access shaft was built at JWPCP so Rachel could be lowered below ground to her starting depth. This shaft is also used to remove excavated soil and to move personnel and materials in and out of the tunnel.

In April 2021, a launch event unveiled Rachel to the public. At this event, the winners of TBM naming and art contests for Los Angeles County students were recognized. The name Rachel was submitted in honor of Rachel Carson, the environmental pioneer and author of Silent Spring. Winning artwork was also displayed on Rachel’s side.

Last summer, Rachel was lowered down the access shaft, assembled and tested. Later that fall, she began her four-year journey to Royal Palms Beach. As of the time of this writing, more than 1,500 feet of tunnel had been completed. Along the tunnel alignment, a variety of sensors have been installed to ensure that tunneling does not impact the surface. These sensors provide real-time data that can be used to adjust tunneling. •

The Clearwater Project is expected to be completed in 2027. For more information on the Clearwater Project and to keep up with Rachel, please visit www.clearwater.lacsd.org.