Wet winter weather is exacerbating an already stinky situation for San Diego County, where a slurry of sewage has been seeping across the southern border for the past two weeks.   

“What I expect is that they double the volume of wastewater over the wet days that we are anticipating,” Hassan Davani, an assistant professor of water resources engineering at San Diego State University, told The Hill. 

The sewage influx is the result of a pipeline rupture across the border in Tijuana that began on Feb. 10, according to the International Boundary and Water Commission (IBWC), a U.S.-Mexican entity that oversees shared water resources. 

Water infrastructure worldwide always has a certain number of cracks and holes — meaning that rainfall can easily infiltrate these systems, Davani explained. So when an inordinate amount of sewage is already polluting a populous shoreline, a winter downpour is bound to make things messier.

“That means more and more wastewater to have to be handled,” Davani said. 

The leakage began in Tijuana when a private developer accidentally damaged a 60-inch pipeline south of the city, leading the State Commission of Public Services of Tijuana to shutter pumping stations in its water conveyance system, the IBWC reported. 

That closure ultimately led “to transboundary flow in the canyons along the U.S.-Mexico border and Tijuana River as well as discharge of wastewater to the coast in Mexico,” per the IBWC.

For nearly two weeks, raw sewage was gushing toward Southern California’s coast, shutting down shorelines in Border Field State Park, Tijuana Slough National Wildlife Refuge, Imperial Beach and Silver Strand on Coronado Island, just south of San Diego. 

On Wednesday evening, the IBWC reported that authorities in Tijuana had completed scheduled repair work, successfully diverting the flow from the broken conduit into a parallel pipeline and resuming pump operations. 

“Wastewater flows are returning to normal and excess flows into the South Bay International Wastewater Treatment Plant will be reduced,” a statement from the IBWC said, referring to a treatment plant in San Diego County that treats some of Tijuana’s sewage.

Nonetheless, a massive amount of sewage had already leaked just in time for an unusual bout of winter weather to sweep through the region. 

Rainfall that began pummeling the area on Wednesday was expected to continue through Saturday, with meteorologists forecasting up to five feet of snow in the county’s mountains. 

“Even if it’s fixed, like 100-percent fixed, [for] at least 72 hours, the water is highly polluted for any activity,” Davani said. “Even if they fix the pipe, the bacteria that was released the past few days — that’s still in the environment.”

While the root of this specific leakage has now been repaired, the incident speaks to a broader trend of infrastructural breakdowns that regularly shuttle Tijuana’s sewage toward San Diego.

“I won’t be surprised to hear next few days, next week or anytime in the future [that] there are additional raw wastewater discharges into the Tijuana River from the Mexico side,” Davani said. 

“What they’re dealing with is basically the lack of infrastructure capacity,” he added.

The Tijuana River Watershed originates in the U.S., before crossing the border into Mexico and then returning north to California once again.

“Anytime they have any raw sewage discharge to the Tijuana River, it ends up being in U.S.,” Davani said. “That’s just the nature of that watershed — it’s sloped that way.”

Although the Tijuana River watershed begins and ends in the U.S., about 75 percent of the basin is located in Mexico, according to the California Water Boards.

The watershed passes through the “densely urbanized city of Tijuana” before draining into the Tijuana River estuary in California and ending up in the Pacific Ocean via Imperial Beach.

Asked if the sewage flow situation could get worse during the ongoing storm, Gabriela Muñoz Melendez, a professor at Tijuana’s College of the Northern Frontier, told The Hill in an email: “Storms always cause chaos in Tijuana due to uncontrolled urbanization, lack of services and socially constructed risk.”

Earlier this week, courts finalized a longstanding legal settlement related to Tijuana’s sewage spread — closing a case that Imperial Beach, Chula Vista and the Port of San Diego had launched against the American contingent of the IBWC.

The case, settled in April 2022, had alleged that the IBWC violated the Clean Water Act by failing to prevent transboundary sewage flows into the Tijuana River Valley, according to a press release issued this week by the Port of San Diego.

As part of the settlement, the plaintiffs dismissed the Clean Water Act claims, while the IBWC began taking steps to mitigate the impacts of transboundary water contamination.

“We are committed to working collaboratively with the federal government to solve, once and for all, one of the worst water pollution crises in America,” Imperial Beach Mayor Paloma Aguirre said in a statement.

Among the actions being taken by the IBWC are the installation and maintenance of temporary “sediment berm” — stone filters made of loose gravel — to stop dry weather transboundary flows, according to the press release.

The IBWC also agreed to perform daily inspections and cleaning of wastewater flow collectors in conjunction with the Tijuana public services commission, as well as install water monitoring catch basins at each collector.

Also included in the settlement was the implementation of a plan for spillages at a particularly problematic collector, and the publication of flow events on social media.

In addition to the IBWC’s plans, the U.S. Environmental Protection Agency has invested $300 million as part of the U.S.-Mexico-Canada Agreement, which will in part fund the expansion of the South Bay International Treatment Plant, per the press release.

“Implementation of the settlement agreement is well underway,” IBWC Secretary Sally Spencer told The Hill in an emailed statement.

“We’ve purchased additional equipment that can be deployed in either country to respond to any problems that arise,” she continued. “We’ve also ramped up our reporting and outreach on transboundary flow events and response.”

Regarding the recent rupture, Spener announced a public meeting next Thursday of the IBWC’s San Diego Citizens Forum. That meeting will include presentations about wastewater collection and treatment upgrades along the San Diego-Tijuana border.

While recognizing that the IBWC is working on these solutions and will eventually add capacity to the international treatment plant, Davani characterized the effort as coming “too late.”

“We’re talking about many more years of raw sewage discharges to our water bodies, both on the U.S. side and Mexico side,” he said, listing a range of public health, business and environmental impacts.

Davani called for more federal and state-level attention to the issue, including expedited action to boost treatment capacity.

Although an infrastructural overhaul on the Mexican side of the border might be ideal, Davani stressed that significant improvements in Baja California are not likely.

“This issue has been there for decades,” he said.

California taxpayers might dislike treating sewage generated in Mexico, but “if they don’t do this, then the wastewater is basically impacting residents of the United States,” Davani explained.

“This needs to be done through cooperation and from both sides of the border,” he said. “It’s a very, very complex issue.”