Sewage has been flowing from Mexico into the Tijuana River and stateside neighborhoods such as Imperial Beach for at least the last two decades. When the Stantec/PCL team initially won the contract to expand the plant in 2025, U.S. IBWC Commissioner Chad McIntosh called the situation unacceptable and promised to fast-track a fix. The $552-million contract remains within the project's original expected $600-million cost, but that figure does not include expansion of the plant's secondary treatment facilities. Frank Fisher, spokesman for the U.S. IBWC, said additional funding will be required to award the secondary treatment work.

"Substantial completion is scheduled for May 2031," said Jeff Newman, operations manager for PCL. "Facilities will be completed throughout the duration of the contract. As facilities are completed they will be placed online to further armor the plant."

Scope changes in the early works package for the first phase of construction include removal and replacement of existing roofs; replacement of process equipment and piping, electrical equipment and odor control media; installation of new window sealants; replacement of coiling doors and emergency showers and eyewash stations; and painting and coating of existing facilities. Long lead-time equipment covered by the revised contract includes standby generators and associated switchgear, medium-voltage switchgear, positive displacement blowers, submersible solids-handling pumps, dewatering centrifuges, stainless steel slide gates and stop logs. Parts of the primary treatment expansion slated to be completed in the 1,643-day construction schedule include a new integrated headworks, a new chemical system, two additional primary sedimentation tanks, a new sludge thickening and storage system and a new 12-kV electrical building with new switchgear and new transformers.

The broader plant expansion also calls for 10 new secondary sedimentation tanks and seven new activated sludge tanks. Those facilities are part of the secondary treatment expansion and are not included in the $552-million award, according to the U.S. IBWC.

Newman said Morley Construction was the successful bidder on the project's large concrete package and PCL will construct some of the ancillary facilities. PCL will self-perform mechanical work, too. Southern Contracting won the electrical work and Technical Systems Incorporated will be the control systems integrator. All long-lead items have been purchased and work is underway on multiple early works packages, Newman said. Shoring, dewatering and excavation of structures for the expansion will begin in the next few weeks, he said.

The Tijuana River Watershed sewage crisis led to groundbreaking research by the Scripps Institute of Oceanography on aerosolized pollutants such as sulfur dioxide off-gassing from riverine hotspots between Tijuana and the Pacific Ocean.

— Bryan Gottlieb contributed reporting to this article