Editor’s note: This story was updated on March 11 with new information. The original story, published March 10, is at the end of this article.
After an excessive flow of wastewater mixed with stormwater entered the United States from Tijuana early Sunday morning, leaders have preliminary information on what happened.
The issue arose during construction on Tijuana’s International Collector, a project that is expected to be complete in early April.
First, at around 11 a.m. on Saturday, a problem installing two inflatable plugs into 72-inch pipes resulted in wastewater flows being diverted to the Tijuana River for about four hours, said Maria-Elena Giner, commissioner for the United States section of the International Boundary and Water Commission, in a statement.
“Another problem occurred at about 1:30 a.m. Sunday due to unexpected wastewater flows in the system coming from two pipes previously unknown to the Tijuana utility,” Giner said. “That sent wastewater mixed with large amounts of rainwater into Stewart’s Drain.”
The flow was estimated at more than 3 million gallons and exceeded the International Collector’s capacity, causing an accumulation of debris that blocked Junction Box 1 of the South Bay International Wastewater Treatment Plant.
“This situation could have jeopardized the plant’s biological treatment system, had it continued,” Giner said. “USIBWC contractor Veolia cleaned the debris so flow could resume to the plant.”
By mid-afternoon Sunday, the transboundary flows had stopped, and the plant resumed normal operations.
During binational meetings Sunday night and Monday morning, Mexico committed to holding daily meetings to keep US officials updated on the progress of the International Collector project and to inform them of any problems that may arise.
A team of technical experts from the IBWC and the Environmental Protection Agency will tour the construction site on Wednesday.
“Mexico has shared with us that construction challenges, as well as heavy rains, may delay the International Collector’s completion,” Giner said.
The International Collector is the largest wastewater conveyance pipe in Tijuana, and it has been plagued by leaks that have caused transboundary flows. Once complete, it will have the capacity to carry up to 60 million gallons per day of untreated sewage to the South Bay International Wastewater Treatment Plant, which is currently being expanded.
Original story:
An excessive flow of wastewater mixed with stormwater began entering the United States from Tijuana early Sunday morning, the US International Boundary and Water Commission reports.
A team from the IBWC, Environmental Protection Agency, and Department of State is working with Mexico to investigate the cause of the transboundary flow.
Leaders are trying to determine whether the transboundary flow is related to Mexico’s work on a new international collector.
The flow was in the vicinity of Stewart’s Drain, which leads to the South Bay International Wastewater Treatment Plant (SBIWTP). The flow caused a buildup of debris that blocked the treatment plant’s Junction Box #1, so little of the flow of wastewater was reaching the plant.
The US requested a meeting with Mexico on Sunday evening to determine the cause of the flow and will provide updates as available, the IBWC said in a statement.
The flow began at about 1:30 a.m. Sunday, and by 2:30 p.m., flow to the treatment plant was increasing and Stewart’s Drain had returned to normal.
As Mexico has improved the infrastructure on its side of the border that contributes to the ongoing Tijuana sewage crisis, construction has at times inadvertently overloaded other parts of the sprawling expanse of infrastructure that treats Tijuana’s wastewater on both sides of the border.
Last summer, for example, an excess of sediment from Mexico began clogging infrastructure at the SBIWTP in San Diego. Mexico at the time said it did not know the source of the sediment, but IBWC leaders suggested it could be related to construction on sewage infrastructure in Mexico.
However, rainfall often increases transboundary flow as well. Last week, a weak atmospheric river brought rainfall to the San Diego area, with Miramar receiving the most precipitation – 2.26 inches – according to the National Weather Service. National City received just over an inch of rain, and Naval Air Station North Island received 0.62 inches.
For example, the January 2024 storm that drenched the county not only caused flooding in Coronado and elsewhere, but it also contributed to the lengthy beach closures in Imperial Beach and Coronado last summer.
Of course, the cause of this transboundary flow event has not yet been identified. This story will be updated as more information is available.
Mexico is finalizing construction on its San Antonio de los Buenos (SAB) Wastewater Treatment Plant, which, after some delays, is expected to be operational in April. The plant will not fully solve the problem, but is expected to put a significant dent in the millions of gallons of untreated wastewater that is dumped into the Pacific Ocean each day.
Meanwhile, the US is expanding and rehabilitating its own international treatment plant. The SBIWTP project will take up to five years to complete. Once finished, the sewage projects planned and underway in the US and Mexico will eliminate an estimated 90 percent of the untreated sewage being dumped into the ocean.
The latest updates on projects related to the sewage crisis is here.
