en.Wedoany.com Reported - The expansion project of the South Bay International Wastewater Treatment Plant in San Diego County, California, has made progress. The design-build team formed by Stantec and PCL Construction utilized 3D models to deliver the plant's pretreatment facility within three months. Since October 2023, more than 31 billion gallons of untreated sewage and contaminated water have flowed from Mexico into the United States, ultimately reaching the Pacific Ocean.
The U.S. Section of the International Boundary and Water Commission, as the treaty-designated agency responsible for managing bilateral water issues, has issued emergency procurements since 2023 to advance the wastewater treatment plant expansion. The United States and Mexico signed Minute No. 328, requiring Mexico to construct new sanitary infrastructure in Tijuana and adopt best practices for wastewater and stormwater management that meet U.S. standards. Chad McIntosh, who became the agency's Chief Commissioner in April 2025, stated: "With the same sense of urgency, we are seeking a permanent solution to the Tijuana River pollution crisis."
A team from the Scripps Institution of Oceanography at the University of California, San Diego, conducted air and water studies from 2023 to 2024. The team led by Kimberly Prather, Distinguished Professor and Director of Atmospheric Chemistry at Scripps, found that the surge in wastewater flows in 2024 intensified the water-to-air transfer of hydrogen sulfide at a turbulent hotspot in the Tijuana River, resulting in nighttime atmospheric peaks reaching thousands of times normal levels. Prather explained: "If you let wastewater flow over steep drops, these gases, especially hydrogen sulfide, are preferentially, almost 100% very efficiently released into the air. That's how wastewater treatment plants purify water, through staged aeration. You shouldn't be doing that in the heart of a community."
Last July, after the Boundary Commission issued a notice to proceed for the 10 million gallons per day (MGD) treatment capacity expansion, the Stantec-PCL team mobilized at the wastewater treatment plant. The expansion includes four main components: a chemically enhanced treatment system that boosts the plant's primary treatment capacity; temporary gravity belt thickeners providing additional sludge thickening capacity; temporary screw presses supplementing solids dewatering capacity; and discharge of treated effluent through the South Bay Ocean Outfall, requiring the opening of additional diffuser ports to accommodate the larger flow. Mike Watson, Alternative Project Delivery Lead for Stantec's water team, stated: "Boundary Commission staff, PCL, and Stantec worked hard to achieve the 10 MGD treatment capacity increase within 100 days."
PCL Project Director Jeff Newman stated that by August 28, 2025, the plant "achieved the new 10 MGD treatment capacity," and the Boundary Commission began "gradually ramping up" treatment capacity to 35 MGD on September 4. Lee Zeldin, the new Administrator of the U.S. Environmental Protection Agency, has committed $250 million in funding for the plant's total $600 million expansion project.
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