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Why a Mexican sewage treatment plant is sparking hope in Southern California

California’s southernmost surfers are breathing a cautious sigh of relief because Mexico’s military begins the long-awaited reconstruction of a defunct wastewater treatment plant near Tijuana.

The Mexican federal infrastructure project, which broke ground last week, aims to minimize the amounts of raw sewage that has for years been spilling into the Pacific Ocean and contaminating beaches on both sides of the border — sickening thousands of residents and forcing temporary closures at local businesses.

“I can’t surf Imperial Beach. I have to drive like 25 miles each way to go to the cleanest beach,” Paloma Aguirre, mayor of the San Diego County city, told The Hill.

“The reason why I moved to Imperial Beach is — I don’t want to broadcast this — but it has the best waves in all of San Diego,” Aguirre added, noting she hasn’t surfed there since 2021.

Imperial Beach, which sits just a few miles north of the U.S.-Mexico border, has long been plagued by a perennial pollution problem: the flow of untreated effluent from Baja California towns onto the beaches of San Diego County.

Facilitating the flow are both seasonal ocean currents and the Tijuana River Watershed, which originates in the U.S. before heading into Mexico and then returning to California. And climate-driven weather extremes have only made a chronic problem even worse.

While the contamination stems from multiple sources, one of the main culprits is the obsolete San Antonio de los Buenos wastewater treatment plant in the town of Punta Bandera — a Tijuana metropolitan area town about 5 miles south of the border.

The site releases millions of gallons of mostly raw sewage daily into the Pacific Ocean, which carries the waste to California’s nearest beaches, according to The San Diego Union-Tribune.

But vast improvements may be on the horizon after Mexican and U.S. officials announced the start of reconstruction efforts at the site at a groundbreaking ceremony last week.

“We are taking a big step to manage wastewater in Cali-Baja for the well-being of the people of this binational community,” U.S. Ambassador to Mexico Ken Salazar said in a statement following the Jan. 11 event.

Illness, odors and business closures

The city of Imperial Beach, about 10 miles south of downtown San Diego, tends to receive the most sizable slurry of sewage from Baja California — which Aguirre said routinely makes residents sick, sometimes from just breathing the polluted air.

Aguirre said she feels like “the default representative for the entire South Bay on this matter” because she has been actively working to pursue a solution since 2005.

While the pollution has become a chronic issue, unusually wet weather last winter exacerbated the problem — causing fecal matter to flood the streets of Imperial Beach, Aguirre recalled.

“This past year we experienced our first-ever boil water advisory,” Aguirre said. “We had four days of being unable to drink or tap water.”

The boil water advisory occurred because samples nearest to the Tijuana Estuary, just south of the city, tested positive for E. coli, the mayor explained.

“Every single one of our businesses that serves you know, beverages or food had to be shut down,” Aguirre said.

“We never saw that even during COVID,” she added, noting some businesses lost tens of thousands of dollars.


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A local urgent care clinic reported a significant uptick in gastrointestinal illnesses at the time, Aguirre recalled, noting people were “getting sick just by breathing.” She also described a surge in economic, environmental and public health ramifications of the crisis.

Recent research from the Scripps Institution of Oceanography — where Aguirre did her master’s degree — assessed the link between cross-border sewage discharge and human illness in 2017, while also modeling possible mitigation strategies.

Baseline conditions evaluated in the study showed 34,000 individuals — or 3.8 percent of swimmers — becoming ill with norovirus. During peak tourism season, that figure rose to 4.5 percent, which the researchers attributed to south-swell driven plumes of pathogens.

Meanwhile, a recent white paper from San Diego State University — shared with The Hill by Aguirre — explores the potential health impacts of the pathogens spread by sewage and the potential threats associated with toxic chemicals and other emerging contaminants.

The response to this transboundary trouble has been slow, a fact Aguirre in large part attributes to what she described as “zero political will” on the other side of the border.

She recalled getting into “a very public spat” with Francisco “Kiko” Vega, who served as Baja California’s governor two administrations ago, from 2013 to 2019.

“He completely denied the fact that that plant was impacting water quality at all,” Aguirre said.

She recalled the next governor, Jaime Bonilla, pledging to fix the problem but then failing to do so. But when the current governor, Ávila Olmeda, assumed her position, Aguirre said her Baja California colleague promised to rectify the issue at their introductory meeting.

When Mexican President Andrés Manuel López Obrador — whose term ends later this year — understood how the private-public partnership was delaying matters, he pushed the plan forward, according to Aguirre.

“I think he just said, ‘You know what, let’s scratch that. We’re going to tap into our national reserves. And I’m going to hand the project over to the military,’” she added.

A rehabilitation process long in the making

Before embarking on the current reconstruction, Mexico had for years intended to revamp San Antonio de los Buenos via a public-private partnership. But that plan — which would have funneled reclaimed sewage to Baja California vineyards — disintegrated amid water price disputes, according to the Voice of San Diego.

López Obrador scrapped that plan and assigned the project to his country’s Secretariat of National Defense (SEDENA) — a decision he made public at a November press conference with Baja California’s governor, Marina del Pilar Ávila Olmeda.

Tasking SEDENA with the revamp automatically hastens the rebuilding process, Ávila Olmeda said at the time, noting that the military is subject to less bureaucracy than other federal entities.

“Not only will we have the largest and best plant in Baja California, but also one of the most modern in all of Mexico with respect to its operation and infrastructure,” she posted last week on X, the platform formerly known as Twitter, following the ground-breaking.

Fernando Aguado, a SEDENA construction engineer, pledged that his team would finish the project by the end of September, as seen in a video of the event aired by Tijuana Press.

San Antonio de los Buenos, first built in 1988, captures about 25 percent of the sewage generated by the Tijuana metropolitan area, Aguado said.

The restoration of the San Antonio de los Buenos facility was among many the infrastructure initiatives included in the binational Minute 328 — a July 2022 agreement signed by the U.S. and Mexico through the joint International Boundary and Water Commission (IBWC).

Salazar credited Minute 328 for facilitating a cross-border commitment of nearly $500 million for waste-related projects in the San Diego and Tijuana regions. Mexico pledged $33.3 million of that sum to revamp the San Antonio de los Buenos treatment plant.

“The Cali-Baja community embodies our integration and how our nations are interconnected through families, commercial ties and a shared environment,” Salazar said.

Gabriela Muñoz Melendez, a professor at Tijuana’s College of the Northern Frontier, said in an email that she sees the reconstruction as good news for “communities on both sides of the border, mainly for Mexican coastal towns.”

Somewhat diminishing that optimism, however, is the problem that treatment plants in developing countries do not always function properly, she explained.

Muñoz Melendez pointed to a past Congressional Research Service report, indicating water and wastewater utilities can make up around 30 percent to 40 percent of a local government’s energy bill.

“Reconstruction is one thing, and operation and maintenance is another,” she added.

Because López Obrador cannot run in Mexico’s June elections, a Voice of San Diego analysis also expressed concern that the winner “could reshuffle all of his priorities.”

While Aguirre stressed the need to remain vigilant during the reconstruction process and acknowledged there are many “things that could go wrong,” she also expressed some optimism.

“It’s the first time in almost 10-15 years that we’ve actually seen not just the commitment, but actual funding allocated and ground-breaking on a project — it’s huge,” she said.

A local emergency only feds can fix

Going forward, the Imperial Beach mayor emphasized a need to not only ensure the Mexican plant’s revamp occurs as planned, but also to accelerate related endeavors in the U.S.

She referred to a planned expansion of the IBWC’s South Bay Wastewater Treatment Plant, which treats some of Tijuana’s sewage in the U.S., near the border-adjacent San Diego district of San Ysidro.

Congress in 2020 appropriated $300 million toward the renovation, but Aguirre said the facility now requires an added $150 million in repairs. Some sedimentation tanks at the site are so clogged with solids that plants are sprouting out of them, she added.

Hassan Davani, an assistant professor of water resources engineering at San Diego State University, tempered his optimism about the Punta Bandera ground-breaking with the financial straits of the South Bay site.

The future operation of the former “will be nothing but positive for San Diego County residents,” he wrote in an email, noting the facility will help treat some of “the massive wastewater volume.”

“That said, additional funding is still needed to fix and expand the treatment plants on the San Diego County side,” he added.

And those extra funds are “contingent on congressional approval,” Aguirre continued, noting that she will be in Washington, D.C., next week, to advocate for more support.

President Biden this past October requested an additional $310 million for the region in an emergency supplemental bill, but that sum has yet to receive congressional approval.

San Diego County in June issued a proclamation of local emergency due to the contamination, but Aguirre lamented the fact Gov. Gavin Newsom (D) has not done so at the state level. Mayors in the region in September then appealed to the governor for “a coordinated State and Federal Emergency Declaration” to address what they deemed a “dire situation.”

Neswom’s legal affairs secretary, David Sapp, explained the reason why such a declaration could not occur in an October letter to the California Coastal Commission, where Aguirre represents the San Diego Coast. Sapp described the governor’s emergency powers as “inapplicable” to this case, as they only “extend to waiving only state statutes and regulations.”

“A state proclamation of emergency cannot accelerate federal work needed on this federal facility that is in a federally-controlled area on an international border,” the letter stated.

Asked if the governor’s office had any further comment on the issue, Alex Stack, deputy communications director, told The Hill in an email that officials explained the state’s role in the letter and at a related Coastal Commission hearing.

Stack cited multiple examples of Newsom’s efforts to rectify the crisis, such as his role in obtaining a September pledge from the IBWC and Environmental Protection Agency to expedite South Bay’s rehabilitation. Also of note was the governor’s $32.2 million investment in the region for mitigation initiatives like debris removal and coastal cleanup.

“The Newsom Administration has been focused on getting more federal resources to rehabilitate and expand the federal facility, which the Biden-Harris Administration included in emergency supplemental funding,” Stack said, adding that these efforts would bolster the already allocated federal funds.

As far as the Punta Bandera facility is concerned, he stressed that “this is exactly the sort of progress we need to address this federal and international crisis.”

Regardless of the response from the governor’s office, Aguirre said she is nonetheless continuing to push for a state of emergency, which she said is “a huge priority for the Coastal Commission as well.”

Stressing that Imperial Beach has been closed for almost 800 days in a row, she reiterated how residents — primarily people of color — are enduring perpetual unsanitary conditions.

“This is on par, if not worse than Flint, in a lot of ways,” Aguirre said, referring to a 2014 lead contamination crisis in Flint, Mich. “People of Imperial Beach feel like second class citizens in this great state and nation.”

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