A collapse in a major Tijuana sewage pipeline has sent millions of gallons of raw wastewater surging into the Tijuana River Valley, pushing a South Bay treatment plant far beyond its capacity and driving dangerous levels of hydrogen sulfide gas into surrounding neighborhoods overnight.
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The U.S. International Boundary and Water Commission reported the failure of Tijuana’s Parallel Gravity Line on Friday night. The line conveys wastewater across Tijuana and its collapse sent excessive flows to the South Bay International Wastewater Treatment Plant, which is designed to handle 35 million gallons per day.
The plant sustained flows above 45 million gallons per day for 13 hours over the weekend and peaked above 60 million gallons per day for nine hours — well above its design capacity, USIBWC said.
The surge of untreated wastewater into the Tijuana River Channel produced sharp spikes in hydrogen sulfide emissions in nearby communities. Monitoring data from the San Diego County Air Pollution Control District showed H2S levels at Berry Elementary School reaching 915 parts per billion between 1 and 2 a.m. Tuesday — more than double the four-hour federal acute exposure guideline threshold of 360 ppb.
The California Office of Health Hazard Assessment sets a protective threshold of 30 ppb for sensitive groups, including children and older adults.
The county’s public health officer, Sayone Thihalolipavan, urged residents who live, work or attend school in the area to monitor air quality updates and take steps to limit their exposure.
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USIBWC said it has been in regular contact with Mexican authorities since the collapse was reported and is pressing for repairs to be completed as quickly as possible. Mexico has indicated repairs could be finished by the end of the week, though USIBWC said it continues to push for an accelerated timeline.
The collapse is the second major Tijuana pipeline failure in recent months. In January, the Insurgentes Collector failed and dumped 11.5 million gallons of raw sewage per day into the Tijuana River. That collapse drew sharp criticism from San Diego County Supervisor Paloma Aguirre, who called it “the latest blow in our ongoing public health crisis.”
USIBWC said the latest failure underscores the urgency of Minute 333 and a binational memorandum of understanding signed last year, which sets a strict timeline for Mexico to rehabilitate the Parallel Gravity Line and make other infrastructure upgrades. The line is currently being rehabilitated end-to-end under the binational agreement.
Residents are advised to limit outdoor activity when odors are present, keep windows and doors closed and use air purifiers with HEPA filters and activated charcoal. Those with asthma, COPD or other chronic lung conditions are urged to keep rescue medications on hand.
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